Program Schedule Overhaul

SCHEDULE OVERHAUL

Overhaul yang terjadwal (Schedule overhaul) termasuk dalam pekerjaan perawatan pencegahan (Preventive Maintenance) yang dilakukan berdasarkan interval waktu atau hours meter tertentu yang direkomendasikan oleh factory (Time base maintenance). Interval waktu pelaksanaan overhaul tersebut juga dapat dipengaruhi oleh beberapa factor, antar lain: kondisi medan operasi, kondisi beban / load, periodic service yang dilakukan, keterampilan operator dan lain-lain.

Schedule overhaul dilaksanakan dengan tujuan untuk merekondisi machine atau komponen kembali pada kondisi standar sesuai dengan standar factory.

RUANG LINGKUP PEKERJAAN OVERHAUL

Lingkup pekerjaan overhaul itu sendiri meliputi: Receiving component, disassembly, washing & cleaning, measurement, parts ordering sesuai standar part overhaul, assembly, testing & adjusting untuk mendapatkan performance kembali standar.

A. RECEIVING & INSPECTION

Receiving & inspection adalah pekerjaan yang harus dilakukan sebelum komponen dilakukandisassembly.

Receiving terhadap komponen yang akan dilakukan overhaul bertujuan untuk mendapatkan data–data yang jelas dari komponen tersebut mengenai kondisi kondisi komponen terhadap: kerusakan, atau kekurangan seperti keretakan (crack), goresan (scratch), penyok (dent), bengkok (bend), maupun hilang (missing), dan sebagainya dengan cara visual check kemudian hasilnya pengecekannya dituangkan dalam lembaran check sheet / QA sheet receiving.

Agar hasil visual check tersebut dapat maksimal, lakukan pre-washing terhadap bagian–bagian yang kotor oleh bocoran oli, grease, coolant maupun bagian yang tertutup dengan tanah atau debu.

B. DISASSEMBLY

Disassembly adalah pekerjaan pembongkaran komponen menjadi sub–sub komponen secara terpisah. Tujuan dari disassembly adalah untuk mendeteksi kerusakan–kerusakan sub komponen, seperti: keausan (worn), kebengkokan (bend), kemacetan (jammed) yang kemungkinan terjadi sehingga mengakibatkan kerusakan yang lebih parah terhadap komponen yang lainnya.

Disassembly juga harus sesuai dengan prosedur yang ada dalam shop manual, untuk menghindari kerusakan komponen saat pelaksanaan pembongkaran. Gunakan shop manual dan special tools yang tepat serta tuangkan data–data hasil disassembly tersebut kedalam QA sheet diassembly. Sub komponen yang masih dapat dipakai kembali ditempatkan pada tempat khusus untuk selanjutnya akan didistribusikan ke section sub komponen atau PTA.

Sedangkan sub–sub komponen yang rusak juga ditempatkan pada tempat khusus untuk dokumentasi dan analisa kerusakan.

C. WASHING & CLEANING

Washing & cleaning adalah pekerjaan yang dilakukan untuk mencuci maupun membersihkan komponen untuk menghilangkan kotoran seperti tanah, debu yang menempel, fuel, oil, grease dan coolant agar komponen menjadi bersih sehingga apabila ada bagian yang rusak seperti retak dan scratch dapat terlihat dengan jelas.

Sebelum washing dilakukan pastikan detergent atau pembersih yang dipakai tepat untuk part atau komponen tersebut dant tidak membuat part atau komponen tersebut rusak atau berubah bentuk (deformation), yang perlu diperhatikan dalam proses washing adalah:

• Washing harus dipisahkan antara small komponen dan large komponen.
• Pilih Deterjen atau chemical yang tepat untuk setiap komponen (missal: chemical yang bersifat basa tinggi jangan dipakai untuk mencuci komponen dari aluminium).
• Jika menggunakan air atau udara bertekanan, sesuaikan tekanannya dengan kotoran yang akan dibersihkan.
• Untuk membersihkan lubang dari kotoran gram – gram keausan gunakan brush yang bersifat magnet.

D. MEASURMENT

Measurment adalah pekerjaan yang wajib dilakukan dalam proses overhaul komponen. Measurment wajib dilakukan dengan menggunakan alat ukur (Special tools) yang sesuai dan kondisinya tidak rusak untuk mendapatkan data yang akurat tentang kondisi komponen tersebut.

Special tools tersebut antara lain: Micro meter, dial gauge, vernier caliper, insulation tester dan sebagainya. Pada tahap proses measurement ini lakukan juga proses inspection atau visual check terhadap bagian yang rawan terhadap keretakan dengan menggunakan alat deteksi keretakan seperti color chek ataupun magnetic flow detector.

Measurement dilakukan untuk mendapatkan data – data akurat berupa angka – angka hasil ukur untuk dibandingkan dengan standarnya.

Hasil perbandingan antara data actual pengukuran dengan maintenance standar akan mendapatkan sebuah kesimpulan bahwa part atau komponen tersebut masih layak untuk dipakai lagi (use again) atau harus di repair sebelum dipasang (use after recondition) atau harus diganti (replace).

Pedoman yang digunakan untuk mengambil kesimpulan tersebut selain dari maintenance standar, juga harus disediakan “guidance for reusable part”.

Untuk memandu mekanik dalam melakukan measurement tersebut digunakan check sheet / QA measurement.

E. PART ORDERING atau RECOMMENDED PARTS

Setelah didapatkan hasil dari inspection dan measurement, maka akan menghasilkan data–data akurat yang akan kita gunakan untuk melakukan recommended parts terhadap part yang kita simpulkan bahwa part tersebut rusak dan harus diganti. Part yang kita order ini adalah part additional atau surcharge (part tambahan), sedangkan satandar part overhaulnya (SPO) sudah lebih dahulu diproses sebelum komponen dibongkar.

Recommended part ini harus mengacu pada part book yang sesuai dengan unit dan komponen tersebut, selain itu gunakan juga parts service news (PSN) apabila ada improvement dari factory. Part order adalah pekerjaan menentukan dan meminta (order) jenis dan jumlah part yang rusak, aus atau hilang saat yang datanya kita dapatkan dari hasil inspection dan measurement.

Untuk mempermudah proses ordering part tersebut maka dibuatkan rangking terhadap part yang sering dipakai dalam proses overhaul tersebut. Lebih detailnya mengenai bagaimana menentukan rangking part dan proses recommended part akan dijelaskan pada materi selanjuttnya.

F. ASSEMBLY

Setelah part yang diorder sudah tersedia, maka part tersebut kita assembly kembali sesuai petunjuk atau langkah-langkah yang ada pada shop manual dengan menggunakan special tools yang sesuai.

Untuk proses assembly ini yang harus kita perhatikan adalah cara atau standar ukuran yang harus ada pada setiap part yang kita pasang tersebut, misalkan standar tightening torque, end play, back lash, protrusion, sinking, clearance dan sebagainya. Standar-standar tersebut dapat kita temukan pada shop manual. Untuk memandu mekanik pelaksana dan menjaga kualitas hasil dalam melakukan proses assembly tersebut digunakan sebuah panduan berupa check sheet assembly / QA assembly.

G. PERFORMANCE TEST (TESTING & ADJUSTING)

Testing adjusting dilaksanakan setelah semua part dan sub komponen selesai dilakukan–assembly secara lengkap kemudian dilakukan pengujian apakah komponen tersebut siap dipakai dan telah mencapai performance yang sesuai dengan factory. Adjusting wajib dilakukan guna mendapatkan standar performance yang optimal dan sesuai dengan kondisi komponen dari factory.

Testing dan adjusting ini dapat dilakukan selama proses assembly maupun pada saat test performance di test bench atau melalui uji secara terpisah sub komponen tersebut, seperti: Fuel Injection Pump (FIP), Alternator, Starting motor dan beberapa komponen lainnya.

H. FINAL CHECK & COMPLETED

Setelah komponen dinyatakan standar atau baik, tahap berikut adalah final check atau pengecekan terakhir terhadap kelengkapan komponen, pengecatan atau painting, pemberian label-label peringatan dan perhatian (labeling) kemudian masking

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Faktor faktor yang mempengaruhi kualitas overhaul

Pentingnya pengendalian kualitas overhaul dalam setiap proses pekerjaan overhaul dapat dijalankan dengan mudah apabila kita mengetahui faktor-faktor apa saja sebenarnya yang bisa mempengaruhi kualitas dari hasil overhaul tersebut.

Berikut adalah gambaran mengenai faktor-faktor yang dapat mempengaruhi kualitas pekerjaan overhaul:

Dari gambaran tersebut diatas, sebenarnya hanya dua faktor saja yang dapat mempengaruhi kualitas pekerjaan overhaul, yaitu:

1. Kedisiplinan dalam penggunaan referensi, dan
2. Kedisiplinan dalam memakai referensi tersebut dengan benar.

Dalam teknis pelaksanaan pekerjaan overhaul harus dilengkapi referensi-referensi yang mendukung agar pekerjaan tersebut dapat berjalan dengan lancar dan parameter-parameter kualitasnya dapat terukur.
Beberapa referensi minimal yang diperlukan tersebut diataranya adalah:

• Shop manual atau service manual atau overhaul manual
• Parts book atau parts katalog
• Parts service news
• Panduan kualitas kerja (PK2)
• Check sheet Quality Control / Quality assurance (QA)
• Common tools
• Specials tools
• Support equipment

Adapun dari sisi non-teknis yang bisa mempengaruhi kualitas pekerjaan overhaul yaitu dari sisi mental atau habit atau prilaku pelaksana overhaul dalam menggunakan referensi-referensi yang sudah ada tersebut apakah dalam prakteknya digunakan dengan sungguh-sungguh atau disiplin.

Sikap mental atau prilaku pelaksana pekerjaan overhaul tersebut dapat dilihat dari bagaimana mereka melaksanakan faktor 5K dengan benar. 5K tersebut adalah:

• Ketelitian
• Kerapihan
• Kebersihan
• Kesegaran
• Kedisiplinan

Penjabaran dari 5K tersebut diatas akan dibahas kusus pada bagian berikutnya. Demikian mengenai faktor faktor yang mempengaruhi kualitas pekerjaan overhaul. Program schedule overhaul yang sudah direncanakan dengan matang dapat berjalan dengan baik apabila kualitas hasil pekerjaan overhaul tersebut "no-redo" dan " reliable" sehingga umur pakainya sesuai yang diharapkan. Semoga kedepan bisa lebih baik.

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Definisi Engine Overhaul

Apa sih sebenarnya definisi dari "Engine Overhaul" ?

Dari sumber-sumber yang saya dapatkan di internet tidak banyak yang menjelaskan secara kongkrit apa itu definisi engine overhaul.

Ada yang menyebutkan bahwa engine overhaul adalah "turun mesin", ada juga yang menyebutkan kalau overhaul adalah service berat / besar, ada juga yang menyebutkan sebagai kegiatan memeriksa dengan teliti untuk memperbaiki keadaan, membuka dan memperbaiki apa yang kurang baik.

Ada satu sumber yang menurut saya bisa kita jadikan acuan yang menyebutkan bahwa definisi engine overhaul (rebuild) adalah suatu prosedur (pekerjaan / program) terorganisir yang dilakukan untuk mengembalikan performa engine ke nilai spesifikasi standar pabrik dan memberikan usia kedua dengan merekondisi komponen yang aus atau rusak mengacu pada petunjuk pemakai ulang (Reusable Parts) komponen menurut standar pabrik.

Dari penjelasan diatas kesimpulannya adalah, bahwa engine overhaul adalah:

• Pekerjaan yang teroganisir (perlu adanya perencanaan yang baik)
• Bertujuan untuk mengembalikan performa engine kembali ke standar pabrik.
• Memberi usia kedua pada engine (menambah umur pemakaian engine)
• Penggantian atau pemakaian ulang komponen / parts mengacu pada petunjuk pemakaian ulang (Guiden for Reusable Parts) yang dikeluarkan oleh pabrik.

Lalu apa saja pertimbangan-pertimbangan untuk dilakukannya suatu pekerjaan engine overhaul dan hal-hal apa saja yang dapat mempercepat interval engine overhaul maupun metode engine overhaul yang bagaimana yang baik untuk dilakukan ?

Tunggu postingan selanjutnya. Jika bermanfaat mohon dibantu sharing melalui FB, G+ atau twitter

Terima kasih.

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Pertimbangan Engine Overhaul (Engine Rebuild)

Pertimbangan untuk dilakukannya engine overhaul.

Overhaul direkomendasikan untuk dilaksanakan sebelum engine mengalami kerusakan, dengan kata lain engine di overhaul dengan penggantian sejumlah parts yang aus dengan parts yang baru.

Parts yang biasanya mengalami keausan tersebut diantaranya: piston ring, rod bearing, main bearing, valve, seat dan lain sebagainya.

Disamping penggantian parts yang telah disebutkan sebelumnya, hal lainnya yang dilakukan sewaktu melakukan overhaul adalah:

• Pemeriksaan menyeluruh atas parts yang lainnya.
• Penggantian seal, gasket, o-ring, packing dan lain sebagainya.
• Pembersihan saluran-saluran di engine block.

"Pengukuran yang nyata, untuk menentukan masa overhaul engine adalah dengan mengukur output tenaga (Power), tekanan kompresi, konsumsi bahan bakar dan konsumsi oli. Jika engine masih memenuhi standar performa tersebut diatas, maka engine tidak perlu untuk dioverhaul meskipun interval jam (Service hour) overhaulnya sudah tercapai".

Berikut ini pertimbangan-pertimbangan untuk dilakukannya overhaul engine:

1. Service Hour

Service hour merupakan nilai rata-rata yang diambil dengan asumsi load faktor engine yang sesuai dengan aplikasinya. Serive hour yang tertera mungkin akan terlalu tinggi jika engine dioperasikan dengan beban yang terlalu tinggi dan mungkin akan terlalu rendah jika engine dioperasikan dengan beban yang terlalu ringan.

Pengurangan jam operasi engine pada kondisi full load tentunya akan menurunkan rata-rata kebutuhan power yang dihasilkan engine. Dan penurunan rata-rata power yang dihasilkan engine akan meningkatkan umur engine dan interval overhaulnya, begitu juga sebaliknya.

Kesimpulannya adalah: pertimbangan untuk overhaul engine berdasarkan service hour bisa terlalu cepat apabila engine dioperasikan dengan kondisi load yang terlalu ringan, begitu juga sebaliknya akan terlalu lama apabila engine dioperasikan dengan kondisi load yang terlalu berat.

2. Total Fuel Consumption

Total fuel consumption merupakan indikasi terbaik yang dapat digunakan dalam menentukan sebuah engine harus di overhaul, meskipun nilai ini meruapakan perkiraan. Fuel consumption lebih mencerminkan pembebanan pada engine, karena saat beban engine meningkat maka fuel consumptionjuga meningkat, begitu juga sebaliknya,

Kesimpulannya adalah: Engine yang beroperasi dengan load yang besar secara terus-menerus akan lebih cepat untuk di overhaul dibandingkan dengan engine yang beroperasi dengan load yang terlalu ringan secara terus menerus, karena dengan load engine yang berbeda pencapaian fuel consumptionnya dalam kurun waktu yang sama juga berbeda.

3. Oil Consumption

Oil consumption juga dapat dipergunakan sebagai indikator untuk menentukan kapan engine harus di overhaul. Konsumsi oli proporsional dengan persentasi beban engine. Ketika persentase beban engine meningkat, jumlah oli yang di konsumsi per jam juga meningkat.

Pada saat oil consumption engine meningkat tiga kali lipat dari nilai konsumsi oli standarnya yang diakibatkan oleh keausan normal, maka engine harus dijadwalkan untuk di overhaul disamping dapat juga di indikasikan oleh meningkatnya tekanan "blowby" dan sedikit peningkatan konsumsi fuel.

Kesimpulannya adalah: Apabila konsumsi oli engine meningkat tiga kali lipat dari nilai standarnya ( misalkan standar konsumsi oli dalam waktu 10 jam operasi adalah 5 liter, sedangkan aktualnya sudah lebih dari 15 liter) sedangkan kebocoran oli keluar (external oil leaked) tidak ada, artinya sudah terjadi oil up dan / atau oil down yang terlalu tinggi, maka engine harus segera di overhaul.

4. Faktor Lainnya

Faktor lainnya yang harus menjadi pertimbangan untuk menentukan kapan waktu engine harus di overhaul disamping faktor ekonomis lainnya, adalah:

• Seberapa konsisten dilakukannya preventive maintenance.
• Kualitas fuel yang di gunakan.
• Kondisi medan operasi
• Hasil laboratorium oil sampling
• Meningkatnya engine noise dan engine vibration.

Demikianlah beberapa pertimbangan yang dapat dijadikan acuan dalam menentukan waktu kapan engine harus di overhaul. Apabila overhaul tidak dilakukan, resiko keausan piston ring, rod bearing, main bearing atau kemungkinan terjadinya kerusakan yang lebih parah akan meningkat.

Lalu hal-hal apa saja yang dapat mempercepat interval waktu overhaul engine ? ikuti pembahasan selanjutnya.

Sumber: TT/009 Engine Rebuild.

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Materi Training Engine CAT C27

Materi Training Engine CAT C27

Berikut ini saya share materi training Engine Caterpillar C27. Materi yang saya share disini berupa E-book dalam aplikasi Android. Bukan E-book pdf seperti biasanya. Jadi tidak dibuka pakai pdf reader, tetapi materi ini langsung install di HP Android dan langsung jalan.

Berikut beberapa screenshoot dari aplikasi tersebut:

Aplikasi setelah terinstall akan tampil icon seperti gambar di atas (CAT C27).

Setelah tombol start di tekan, akan tampil halaman awal dari materi Engine CAT C27 tersebut.

Contoh halaman berikutnya/ halamn 2.

Ada mode "search" yang dapat digunakan untuk mencari topik bahasan yang diinginkan dengan cepat dan memberikan pilihan yang lengkap.

Demikian materi training engine CAT C27 yang saya share, semoga bermanfaat. Apabila ada pertanyaan silahkan sampaikan pada kolom komentar.

Terima kasih.

Download aplikasinya: disini.

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Kuis K3LH Android

Berikut ini admin sharing Kuis K3LH Android dalam bentuk aplikasi Android. Kuis ini berisi materi latihan dalam bentuk soal pilihan ganda dalam tiga kategori, yaitu: Keselamatan, kesehatan dan lingkungan hidup.

Silahkan dicoba untuk menguji tingkat pemahaman kita dalam bidang K3LH.

Semoga bermanfaat.

Aplikasi Kuis K3LH Android tersebut dapat di download disini: https://db.tt/d2GnwF8g

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Mengapa Gas Buang Kendaraan Diesel Berwarna Hitam??

Kendaraan yang bermesin diesel adalah kendaraan yang identik dengan kendaraan yang mengeluarkan gas buang hitam yang sangat menggangu. Lalu mengapa diesel rata-rata mengeluarkan asap hitam dari knalpotnya? Ada beberapa hal yang menjadi penyebab asap hitam dari diesel, antara lain :

1. Saringan udara kotor.

Meskipun volume penyemprotan pada pompa injeksi sudah sesuai, tapi karna saringan udara kotor, maka udara yang masuk ke dalam silinder tidak sebanding dengan solar yang disemprotkan (udara terlalu sedikit). Solar tidak terbakar dengan sempurna, akibatnya asap hitam. Oleh karena itu secara periodikal, bersihkan saringan udara tersebut atau kalau memang sudah rusak perlu penggantian.

2. Bentuk penyemprotan nosel injeksi tidak bagus/ada tetesan

Bentuk penyemprotan yang tidak bagus atau ada tetesan pada nosel injeksi akan menyebabkan solar tidak bercampur dengan udara secara sempurna. Sebagian solar tidak terbakar sehingga asap yang dihasilkan dari kendaraan akan berwama hitam. Maka dari itu, perlu dilakukan pemeriksaan tekanan injeksi, bentuk penyemprotan dan tetesan pada injektor.

3. Saat penyemprotan terlambat

Bila penyemprotan terlambat, solar juga tidak akan terbakar dengan sempurna.

4. Tekanan Turbocharger kurang

Pada motor diesel yang dilengkapi dengan system pengisian udara tekan, pengisian cylinder akan berkurang bila tekanan pengisian kurang. Hal ini disebabkan kerusakan pada turbocharger itu sendiri atau kebocoran pada salurannya.  

5. Knalpot/saluran gas buang tersumbat

Pada motor dengan turbocarjer, knalpot yang tersumbat akan menyebabkan asap hitam. Apabila gas buang tidak keluar silinder dengan lancar, maka udara bersih yang masuk kesilinder berkurang, tetapi jumlah penyemprotan bahan bakar tetap sesuai untuk pengisian udara yang normal. Periksa selalu dan bersihkan knalpot atau ganti bila perlu.

6. Volume penyemprotan tidak sesuai (terlalu banyak)

Sampai batas tertentu, penambahan volume penyemprotan akan menambah daya motor, tapi penambahan volume yang terlalu banyak tidak akan menaikkan lagi daya motor dan akan mengakibatkan asap hitam karena solar tidak terbakar dengan sempurna.

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5 Unsur dalam Gas Buang

Pada negara-negara yang memiliki standar emisi gas buang kendaraan yang ketat, ada 5 unsur dalam gas buang kendaraan yang akan diukur yaitu senyawa HC, CO, CO₂, 0₂ dan senyawa NOx Sedangkan pada negara-negara yang standar emisinya tidak terlalu ketat, hanya mengukur 4 unsur dalam gas buang yaitu senyawa HC, CO, CO₂ dan 0₂.

• Emisi Senyawa Hidrokarbon (HC)

Bensin adalah senyawa hidrokarbon, jadi setiap HC yang didapat di gas buang kendaraan menunjukkan adanya bensin yang tidak terbakar dan terbuang bersama sisa pembakaran. Apabila suatu senyawa hidrokarbon terbakar sempurna (bereaksi dengan oksigen) maka hasil reaksi pembakaran tersebut adalah karbondioksida (CO₂) dan air(H₂0).Walaupun rasio perbandingan antara udara dan bensin (AFR=Air-to-Fuel Ratio) sudah tepat dan didukung oleh desain ruang bakar mesin saat ini yang sudah mendekati ideal, tetapi tetap saja sebagian dari bensin seolah-olah tetap dapat "bersembunyi" dari api saat terjadi proses pembakaran dan menyebabkan emisi HC pada ujung knalpot cukup tinggi.

Untuk mobil yang tidak dilengkapi dengan Catalytic Converter (CC), emisi HC yang dapat ditolerir adalah 500 ppm dan untuk mobil yang dilengkapi dengan CC, emisi HC yang dapat ditolerir adalah 50 ppm.

Emisi HC ini dapat ditekan dengan cara memberikan tambahan panas dan oksigen diluar ruang bakar untuk menuntaskan proses pembakaran. Proses injeksi oksigen tepat setelah exhaust port akan dapat menekan emisi HC secara drastis. Saat ini, beberapa mesin mobil sudah dilengkapi dengan electronic air injection reaction pump yang langsung bekerja saat cold-start untuk menurunkan emisi HC sesaat sebelum CC mencapai suhu kerja ideal.

Apabila emisi HC tinggi, menunjukkan ada 3 kemungkinan penyebabnya yaitu CC yang tidak berfungsi, AFR yang tidak tepat (terlalu kaya) atau bensin tidak terbakar dengan sempurna di ruang bakar. Apabila mobil dilengkapi dengan CC, maka harus dilakukan pengujian terlebih dahulu terhadap CC dengan caramengukur perbedaan suhu antara inlet CC dan outletnya. Seharusnya suhu di outlet akan lebih tinggi minimal 10% dari pada inletnya.

Apabila CC bekerja dengan normal tapi HC tetap tinggi, maka hal ini menunjukkan gejala bahwa AFR yang tidak tepat atau terjadi m isfire. AFR yang terlalu kaya akan menyebabkan emisi HC menjadi tinggi. Ini bisa disebabkan antara lain kebocoran fuel pressure regulator, setelan karburator tidak tepat, filter udara yang tersumbat, sensor temperature mesin yang tidak normal dan sebagainya yang dapat membuat AFR terlalu kaya. Injector yang kotor atau fuel pressure yang terlalu rendah dapat membuat butiran bensin menjadi terlalu besar untuk terbakar dengan sempurna dan ini juga akan membuat emisi HC menjadi tinggi. Apapun alasannya, AFR yang terlalu kaya juga akan membuat emisi CO menjadi tinggi dan bahkan menyebabkan outlet dari CC mengalami overheat, tetapi CO dan HC yang tinggi juga bisa disebabkan oleh rembesnya pelumas ke ruang bakar.

Apabila hanya HC yang tinggi, maka harus ditelusuri penyebab yang membuat ECU memerintahkan injector untuk menyemprotkan bensin hanya sedikit sehingga AFR terlalu kurus yang menyebabkan terjadinya intermittent misfire. Pada mobil yang masih menggunakan karburator, penyebab misfire antara lain adalah kabel bus i yang tidak balk, timing pengapian yang terlalu mundur, kebocoran udara disekitar intake manifold atau mechanical problem yang menyebabkan angka kompresi mesin rendah.

Untuk mobil yang dilengkapi dengan sistem EFI dan CC, gejala misfire ini harus segera diatasi karena apabila didiamkan, ECU akan terus menerus berusaha membuat AFR menjadi kaya karena membaca bahwa masih ada oksigen yang tidak terbakar ini. Akibatnya CC akan mengalami overheat.

• Emisi Carbon Monoksida (CO)

Gas karbonmonoksida adalah gas yang relative tidak stabil dan cenderung bereaksi dengan unsur lain. Carbon monoksida, dapat diubah dengan mudah menjadi CO₂ dengan bantuan sedikit oksigen dan panas. Saat mesin bekerja dengan AFR yang tepat, emisi CO pada ujung knalpot berkisar 0.5% sampai 1% untuk mesin yang dilengkapi dengan sistem injeksi atau sekitar 2.5% untuk mesin yang masih menggunakan karburator. Dengan bantuan air injection system atau CC, maka CO dapat dibuat serendah mungkin mendekati 0%.

Apabila AFR sedikit saja lebih kaya dari angka idealnya (AFR ideal = lambda = 1.00) maka emisi CO akan naik secara drastis. Jadi tingginya angka CO menunjukkan bahwa AFR terlalu kaya dan ini bisa disebabkan antara lain karena masalah di fuel injection system seperti fuel pressure yang terlalu tinggi, sensor suhu mesin yang tidak normal, air filter yang kotor, PCV system yang tidak normal, karburator yang kotor atau setelannya yang tidak tepat.

•  Emisi Karbon Dioksida (CO₂)

Konsentrasi CO₂ menunjukkan secara langsung status proses pembakaran di ruang bakar. Semakin tinggi maka semakin baik. Saat AFR berada di angka ideal, emisi CO₂ berkisar antara 12% sampai 15%. Apabila AFR terlalu kurus atau terlalu kaya, maka emisi CO₂ akan turun secara drasfis. Apabila CO₂ berada dibawah 12%, maka kits harus melihat emisi lainnya yang menunjukkan apakah AFR terlalu kaya atau terlalu kurus.

Perlu diingat bahwa sumber dari CO₂ ini hanya ruang bakar dan CC. Apabila CO₂ terlalu rendah tapi CO dan HC normal, menunjukkan adanya kebocoran exhaust pipe.

•  Oksigen (O₂)

Konsentrasi dari oksigen di gas buang kendaraan berbanding terbalik dengan konsentrasi CO2. Untuk mendapatkan proses pembakaran yang sempuma, maka kadar oksigen yang masuk ke ruang bakar harus mencukupi untuk setiap molekul hidrokarbon.

Dalam ruang bakar, campuran udara dan bensin dapat terbakar dengan sempurna apabila bentuk dari ruang bakar tersebut melengkung secara sempurna. Kondisi ini memungkinkan molekul bensin dan molekul udara dapat dengan mudah bertemu untuk bereaksi dengan sempurna pada proses pembakaran. Tapi sayangnya, ruang bakar tidak dapat sempuma melengkung dan halus sehingga memungkinkan molekul bensin seolah-olah bersembunyi dari molekul oksigen dan menyebabkan proses pembakaran tidak terjadi dengan sempurna.

Untuk mengurangi emisi HC, maka dibutuhkan sedikit tambahan udara atau oksigen untuk memastikan bahwa semua molekul bensin dapat "bertemu" dengan molekul oksigen untuk bereaksi dengan sempuma. Ini berarti AFR 14,7:1 (lambda = 1.00) sebenamya merupakan kondisi yang sedikit kurus. Inilah yang menyebabkan oksigen dalam gas buang akan berkisar antara 0.5% sampai 1%. Pada mesin yang dilengkapi dengan CC, kondisi ini akan baik karena membantu fungsi CC untuk mengubah CO dan HC menjadi CO₂.

Mesin tetap dapat bekerja dengan baik walaupun AFR terlalu kurus bahkan hingga AFR mencapai 16:1. Tapi dalam kondisi seperti ini akan timbul efek lain seperti mesin cenderung knocking, suhu mesin bertambah dan emisi senyawa NOx juga akan meningkat drastis.

Normalnya konsentrasi oksigen di gas buang adalah sekitar 12% atau lebih kecil bahkan mungkin 0%. Tapi kita harus berhati-hati apabila konsentrasi oksigen mencapai 0%. Ini menunjukkan bahwa semua oksigen dapat terpakai semua dalam proses pembakaran dan ini dapat berarti bahwa AFR cenderung kaya. Dalam kondisi demikian, rendahnya konsentrasi oksigen akan berbarengan dengan tingginya emisi CO. Apabila konsentrasi oksigen tinggi dapat berarti AFR terlalu kurus tapi juga dapat menunjukkan beberapa hal lain. Apabila dibarengi dengan tingginya CO dan HC, maka pada mobil yang dilengkapi dengan CC berarti CC mengalami kerusakan. Untuk mobil yang tidak dilengkapi dengan CC, bila oksigen terlalu tinggi dan lainnya rendah berarti ada kebocoran di exhaust sytem.

•  Emisi senyawa NOx

Selain keempat gas diatas, emisi NOx tidak dipentingkan dalam melakukan diagnose terhadap mesin. Senyawa NOx adalah ikatan kimia antara unsur nitrogen dan oksigen. Dalam kondisi normal atmosphere, nitrogen adalah gas inert yang amat stabil yang tidak akan berikatan dengan unsur lain. Tetapi dalam kondisi suhu tinggi dan tekanan tinggi dalam ruang bakar, nitrogen akan memecah ikatannya dan berikatan dengan oksigen.

Senyawa NOx ini sangat tidak stabil dan bila terlepas ke udara bebas, akan berikatan dengan oksigen untuk membentuk NO₂. Inilah yang amat berbahaya karena senyawa ini amat beracun dan bila terkena air akan membentuk asam nitrat.

Tingginya konsentrasi senyawa NOx disebabkan karena tingginya konsentrasi oksigen ditambah dengan tingginya suhu ruang bakar. Untuk menjaga agar konsentrasi NOx tidak tinggi maka diperlukan kontrol secara tepat terhadap AFR dan suhu ruang bakar harus dijaga agar tidak terlalu tinggi baik dengan EGR maupun long valve overlap. Normalnya NOx pada saat idle tidak melebihi 100 ppm. Apabila AFR terlalu kurus, timing pengapian yang terlalu tinggi atau sebab lainnya yang menyebabkan suhu ruang bakar meningkat, akan meningkatkan konsentrasi NOx dan ini tidak akan dapat diatasi oleh CC atau sistem EGR yang canggih sekalipun.

Tumpukan kerak karbon yang berada di ruang bakar juga akan meningkatkan kompresi mesin dan dapat menyebabkan timbulnya titik panas yang dapat meningkatkan kadar NOx.  Mesin yang sering detonasi juga akan menyebabkan tingginya konsentrasi NOx.

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AUTOMOTIVE TECHNICAL TERMS C

CALCULATED LOAD VALUE
A scan tool PID that indicates engine load. It is the percentage of engine capacity being used based on current airflow divided by maximum airflow.

CAMBER
A wheel alignment angle that refers to the inward or outward tilt of the wheels as viewed from the front. Outward tilt is called "positive" camber while inward tilt is called "negative." Ideally, the wheels should have zero rolling camber (perpendicular to the road) when the vehicle is loaded. Camber changes as the vehicle is loaded and the suspension sags. To compensate, the static alignment specifications may call for a slight amount of positive or negative camber depending on how the suspension is built (See Alignment). On vehicles with independent rear suspensions, excessive negative camber often results with the vehicle is overloaded. Excessive camber can cause uneven tread wear on the tires (one side will be worn more than the other). Camber can be affected by worn suspension components such as control arm bushings and ball joints, or by bent parts such as a MacPherson strut. Camber is changed by adding or subtracting shims from the control arm pivot mounts, or on strut cars by moving the top or bottom of the strut in or out. See Wheel Alignment.

CAMBER ROLL
The change in camber that occurs when the front wheels on a vehicle with an independent suspension are steered to either side. The amount of camber change that occurs is affected by the amount of caster. Some camber change is good because it causes the tires to lean into a turn for better handling and traction. But too much camber change can accelerate shoulder wear on the tires.

CAMBER WEAR
Tire wear that occurs on one side of the tread because the tire is leaning in or out. The underlying cause may be worn control arm bushings, a weak or sagging spring or a badly worn ball joint.

CAMBER BOLT
A bolt fitted with an eccentric that is turned to change a wheel's camber setting.
Camber bolts are typically used on control arms and lower strut mounts.

CAMSHAFT
A shaft inside an engine that has lobes to operate the engine's valves. In "pushrod" engines, lifters ride on the cam lobes. The up and down motion is transferred through push rods and rocker arms to actuate the valves (See Lifters). In an "overhead" cam engine, the cam may push directly on the tops of the valves or work the valves through short rocker arms. Loss of lubrication (low oil) or dirty oil can cause scuffing and lobe wear on a cam. The result is loss of engine power because the affected valves do not open completely. The only cure is to replace the cam, a job that requires more advanced skills. The cam may also be changed to improve performance and/or fuel economy. Aftermarket camshafts offer a wide range of different lobe profiles from which to choose. A higher lift, longer duration cam generally provides more power and moves the engine's peak power point up the rpm scale. See Camshafts.

CARBON DIOXIDE (CO2)
A harmless, odorless gas composed of carbon and oxygen. It is the byproduct of complete combustion. But it is also a greenhouse gas that contributes to global warming.

CARBON MONOXIDE (CO)
A deadly gas that results from the incomplete burning of gasoline inside the engine, carbon monoxide is considered to be a serious air pollutant. You can't see it or smell it, but it can kill in very small concentrations. Because of this you should never run an engine inside a closed garage. Various means are used to reduce the amount of CO produced by an engine, and primary among these is the catalytic converter. The converter "reburns" CO in the exhaust and converts it into harmless carbon dioxide.

CARBURETOR
A component used to deliver air and fuel on older engines. It mixes air and fuel in varying proportions according to the position of the throttle opening and engine vacuum. Carburetor adjustments include idle speed, idle fuel mixture and choke setting. Most carburetor problems are due to choke misadjustment or dirty air or fuel. Dirt can plug up the tiny metering orifices, resulting in a variety of derivability problems. Wear around the throttle shafts or warpage or vacuum leaks around the base plate can also cause problems. Overhaul kits are available, but many carburetors can be very difficult to rebuild correctly. A better alternative is a factory rebuilt carburetor that can be easily installed. See Carburetor Diagnosis.

CARDAN JOINT
Also known as a Hooke Joint, Universal Joint or U-Joint, it is a simple flexible coupling using a double yoke and four-point center cross. Cardan joints are used as couplings in the driveshafts of rear-wheel drive cars. Because they can produce uneven shaft speeds when operated at joint angles of more than a few degrees, they are usually not used with front-wheel drive (because the front wheels also steer and create large operating angles).

CASTER
A wheel alignment angle that refers to the forward or rearward tilt of the steering axis on the front wheels (See Alignment). A forward tilt of the steering axis is called "negative" caster while a rearward tilt is called "positive." The caster angle has no affect on tread wear but it does affect steering return and stability. Most vehicle have a certain amount of positive caster. The higher the caster angle the more steady the car feels at high speed (Mercedes, for example, uses a very high caster setting). But the higher the caster angle, the greater the steering effort. The caster angle on many strut suspensions is fixed at the factory and is not adjustable. See Wheel Alignment.

CASTER SHIMS
Small wedge shaped shims that fit between a leaf spring and solid axle to change caster. Used primarily on trucks with a solid front axle or four-wheel drive.

CATALYTIC CONVERTER
The converter is an emissions control device in the exhaust system that reduces the amount of pollutants that come out the tailpipe. It does this by reburning certain pollutants and reforming others. Platinum, palladium and rhodium catalysts act as triggers for the chemical reactions. Catalytic converters were first used on 1975 model year cars to reduce hydrocarbon and carbon monoxide emissions. In 1981, a new type of "three-way" converter was installed to also reduce oxides of nitrogen. The converter does a superb job of reducing pollutants, but the catalyst can be contaminated with lead (from leaded gasoline) and phosphorus (from burning oil), or silicone (from internal coolant leaks). The converter is covered by an 8 year/100,000 mile emissions warranty. It is illegal to remove a catalytic converter. If replacement is necessary, it must be replaced with the same type of converter as the original. See Catalytic Converters.

CENTER BOLT
The bolt that maintains the alignment of the leaves in a leaf spring, and the position of the axle on the springs.

CENTERLINE
The geometric center of the suspension defined by a line that runs the length of the vehicle and bisects the midpoints of the front and rear axles. Used as a reference line in alignment for measuring toe and thrust angle.

CENTER LINK
The center bar or link in a parallelogram steering system that connects the pitman arm and idler arm. Also called a "relay rod."

CENTER OF GRAVITY
An imaginary point around which the weight of a vehicle is centered. A lower center of gravity improves handing stability and cornering agility. The center of gravity can be lowered by installing shorter suspension springs and/or low profile tires.

CENTRIFUGAL ADVANCE
A mechanical means of advancing spark timing with flyweights and springs to compensate for changing engine speed (rpm). The weights are located inside the distributor on older vehicles with electronic (noncomputer) ignition systems. The size of the weights, the amount of spring tension, and engine rpm determine the rate and amount of advance. Advancing the spark timing as engine speed increases is necessary for good fuel economy and performance.

CHASSIS
The frame or undercarriage of a vehicle. On unibody vehicles, the lower structure to which the suspension is attached.

CFC CERTIFICATION
A process whereby technicians take an EPA approved course on R12 recovery and recycling, and pass a written examination. CFC certification is required to work on all A/C systems, but no additional certification is required for servicing R134a systems.

CHANGE OF STATE
The rearrangement of the molecular structure of matter as it changes from one physical state to another (solid, liquid or gas). Also called a "phase" change.

CHARCOAL CANISTER
A storage device in the evaporative emissions control system. It is a small cylindrical or rectangular container that contains activated charcoal particles. The charcoal traps gasoline vapors from the fuel tank (and carburetor on older vehicles). Later, the vapors are purged and drawn into the engine when the vehicle is being driven. See EVAP System.

CHARGE
A specific amount of refrigerant or compressor oil by weight. This is specified by the vehicle manufacturer for individual A/C system applications.

CHARGING SYSTEM
The charging system includes the alternator, voltage regulator which is often a part of the alternator itself), the battery, and the indicator gauge or warning light on the dash (See Alternator, Battery and Voltage Regulator). The charging system's job is to generate enough current to keep the battery fully charged, and to satisfy the demands of the ignition and electrical systems. The voltage regulator senses the demands on the electrical system, and controls alternator output so sufficient current is produced. A loose V-belt, or a defective alternator or voltage regulator can cause the dash warning light to glow red (or the amp gauge to show and steady discharge). If the problem is not corrected, the battery will run down and eventually go dead. See Charging System Checks.
 
CHECK ENGINE LIGHT
A warning light that comes on if the computerized engine control system detects an engine performance or emissions problem. Also called the "malfunction indicator lamp" (MIL). To determine the nature of the problem, the computer system must be accessed to read a fault code. See Check Engine Light.

CHECK VALVE
A valve which permits the passage of a gas or fluid in one direction, but not in the other. For example, the check valve between the air pump and exhaust manifold in an air injection system allows air to flow to the manifold, but stops exhaust gas from entering the air pump in the event that the pump belt breaks. A check valve in the master brake cylinder allows brake fluid to flow in one direction only.

CHOKE
A little flap-like valve in the top of a carburetor that opens and closes to control the amount of air entering the carburetor when the engine is cold. The choke's purpose is to artificially enrich the fuel mixture (by choking off the air supply) during starting and engine warm-up. If the choke is not adjusted correctly, it can make the engine hard to start and/or stall. See Carburetor Diagnosis.

CHLOROFLUOROCARBONS (CFCs)
A family of manmade chemicals containing chlorine that include R12 automotive air conditioning refrigerant. CFCs have been blamed for a deterioration of the Earth�s protective ozone layer. CFCs have been phased out of production by international agreement.

CIRCUIT BREAKER
A protective device that�s often used in a wiring circuit to protect against overloads. A circuit breaker has a bimetallic arm and a pair of contact points. When the current exceeds its preset limits, the arm gets hot, bends and opens the contact points. This shuts off the current through the circuit and protects against damage or fire. Most circuit breakers automatically reset themselves after they cool down, but some have a button that must be manually reset to restore power. Circuit breakers are often used in the headlight and air conditioning circuits.

CLOSED LOOP
The basic principle of electronic engine management in which input from an oxygen sensor allows the engine control computer to determine and maintain a nearly perfect air-fuel ratio. To enter closed loop operation, the oxygen sensor must be producing a voltage signal and the engine must have reached a certain operating temperature. Sell also Open Loop.

CLUTCH
A device that couples the engine to the transmission. The clutch consists of a friction-lined disk (called the "clutch disk") and a spring-loaded "pressure plate" that presses the clutch disk tightly against the flywheel (See Flywheel). When you push in on the clutch pedal, the linkage releases the spring pressure allowing the clutch disk to slip. The clutch disk is subjected to a tremendous amount of friction and heat, which eventually wears it out. At this point it starts to slip. Oil or grease on the flywheel, weak or broken springs in the pressure plate, or overadjusted linkage can also make it slip. If it fails to release, the most likely cause is a broken clutch cable or a leaky hydraulic linkage. See Common CLutch Problems.

COIL-ON-PLUG IGNITION (COP)
A type of distributorless ignition system where individual ignition coils are mounted directly over each spark plug. No spark plug wires are used. See COP Ignition.

COIL SPRINGS
A type of spring made of wound heavy-gauge steel wire used to support the weight of the vehicle. The spring may be located between the control arm and chassis, the axle and chassis, or around a MacPherson strut. Coil springs may be conical or spiral wound, constant rate or variable rate, and wound with variable pitch spacing or variable thickness wire. Coil springs sag with age, and sometimes break. Replacement in pairs is recommended to maintain even ride height side-to-side.

COMPLIANCE
The "give" or flexing that occurs in the suspension and steering due to the compression of rubber bushings and joint play. A small amount of compliance is desirable because it absorbs shocks and dampens vibrations to reduce steering feedback and harshness. But too much compliance can make the steering feel vague and mushy (unresponsive), while also contributing to toe wear by allowing excessive changes in toe alignment.

COMPRESSION
The amount by which the air volume in a cylinder is reduced or compressed by the upward stroke of the piston. See Compression Ratio. Compression can be measured mechanically by installing a compression gauge in a spark plug hole, disabling the ignition and cranking the engine, or electronically by an engine analyzer during a cranking test. See Compression Testing.

COMPRESSION RATIO
The relationship between the piston cylinder volume from bottom dead center to top dead center. Higher compression ratios improve combustion efficiency but also require higher-octane fuels. Pre-emission control engines often had compression ratios as high as 11.5:1 whereas most of today's engines are between 8.5:1 and 9.5:1. Diesel engines have very high compression ratios, from 18:1 to 22:1.

COMPRESSOR
The refrigeration system component that pumps refrigerant and increases the pressure and temperature of refrigerant vapor. The compressor is belt driven via a magnetic clutch, and may be a piston or scroll type design. A compressor failure can throw metallic debris into the A/C system that can damage a replacement compressor unless the condenser is cleaned by flushing or replaced. See Compressor Failures.

COMPRESSOR CYCLING SWITCH
See Thermostatic Switch.

COMPRESSOR CUTOFF SWITCH
A low pressure cutoff switch in a CCOT refrigeration circuit that reacts to low head pressure and opens the compressor clutch circuit to disengage the compressor if the system loses its charge of refrigerant. Some systems also have a separate high pressure cutoff switch (or a combination high-low pressure switch) that opens the compressor clutch circuit if system pressure exceeds a preset limit.

COMPRESSOR OIL
The oil within the A/C system that lubricates the compressor. R12 systems use a special type of mineral oil. R134a systems use either a PAG or ester-based oil. A certain amount of compressor oil must be in the system at all times to prevent compressor damage. Loss of compressor oil (or failure to replace oil that was lost during the service or replacement of system components) will in compressor failure. Too much oil in the system can cause loss of cooling efficiency or compressor failure. See PAG Oil Recommendations.

COMPUTERIZED ENGINE CONTROLS
A microprocessor based engine management systems that utilizes various sensor inputs to regulate spark timing, fuel mixture, emissions and other functions. Used on most vehicles since 1981 to comply with federal emission regulations. Diagnosis usually requires accessing trouble codes and/or putting the system into a special diagnostic mode. See Engine Management Systems and PCMs.

CONDENSATION
The process whereby a vapor changes to a liquid. This requires a "cooling effect" to draw heat away from the vapor. When the temperature of the vapor reaches a certain point, droplets of liquid (condensate) begin to form. Condensation of the refrigerant vapor takes place in the condenser.

CONDENSER
The refrigeration system component that changes refrigerant vapor to a liquid by removing heat. The condenser is an air-to-air heat exchanger consisting of metal tubes and cooling fins. It is usually mounted just ahead of the radiator, and may have its own cooling fan.

CONDUCTION
The transmission of energy (heat) through a medium without perceptible motion of that medium (direct contact).

CONSTANT VELOCITY (CV) JOINT
A Constant Velocity Joint is one that provides consistent driveshaft speeds regardless of the operating angle of the joint. CV joints are used primarily in on the driveshafts of front-wheel drive vehicles, and they come in two basic varieties: the Rzeppa ball type joints (which you will find on the outer end of the driveshaft) and tripod joints (which are used on the inner end). See CV Joints.

CONTROLLER AREA NETWORK (CAN)
CAN is essentially an engineering standard for how computers and modules talk to one another via the serial data bus in a vehicle's wiring system. It's a high speed standard designed for powertrain control modules, antilock brakes and stability control systems. It is used on a growing number of 2003 and newer vehicles. See CAN systems.

CONTROL ARMS
Suspension components which connect the steering knuckles to the chassis or subframe, and allow the knuckles to move up and down.

CONVECTION
The transfer of heat by the circulation of a liquid or vapor

COOLANT
The liquid inside the radiator and cooling system is called the "coolant" because it cools the engine. It circulates through the engine and soaks up heat. The coolant then flows to the radiator (See Radiator) where it sheds its heat. When the heater is turned on, coolant also flows through the heater core (which acts like a miniature radiator) to heat air entering the passenger compartment. A low coolant level can result in overheating, no heat from the heater, and/or serious engine damage. The coolant level inside the radiator should be checked periodically to replace any that has been lost. The recommended coolant for most vehicles is a mixture of 50% water and 50% antifreeze. Straight water should never be used because it is extremely corrosive, and offers no freezing or boilover protection. See Types of Antifreeze.

COOLANT TEMPERATURE SENSOR
A variable resistance thermistor which changes resistance as the engine's coolant temperature changes. The sensor's output is monitored by the engine computer to regulate various ignition, fuel and emission control functions, and to turn the radiator cooling fan on and off as needed. In the PTC (Positive Temperature Coefficient) type of sensor, ohms go up with temperature. In the more common NTC (Negative Temperature Coefficient) type, resistance goes down as heat goes up. See Coolant Sensors.

COOLING SYSTEM
The cooling system consists of the radiator, water pump, thermostat, heater core, heater and radiator hoses, and the water jackets inside the cylinder head and engine block (See Coolant, Radiator and Water pump). An engine produces a tremendous amount of waste heat when it runs, so some means of cooling is needed to prevent the engine from self-destructing. Some engines (such as lawn mower and small motorcycles) are air-cooled. But liquid-cooling is used for most automotive applications because it is more efficient, it allows better temperature control (for better performance and lower emissions), and it can provide heat in the winter. See Servicing Cooling System.

CRADLE
A structural member used in many front-wheel drive cars that supports the engine and transaxle. The cradle is bolted to the subframe, and is also connected to the lower control arms. The position of the cradle is important because it affects camber and caster.

CRANKCASE EMISSIONS
See blowby, also Measuring Blowby

CRANKSHAFT
The main shaft inside the engine that turns the up-and-down motion of the pistons into rotational torque. There are two types of crankshafts: cast iron and forged steel. The cast variety are used in most passenger car engines while the stronger forged ones are used primarily in high performance applications. When an engine is overhauled, the rod and main bearing journals are reground to restore a smooth surface. Crankshaft failures are fortunately not very common, but when they happen it usually caused by excessive internal engine vibration or defects in the crankshaft itself.
 
CRANKSHAFT POSITION (CKP) SENSOR
A type of sensor used to monitor the position of the crankshaft. The sensor's input is used to trigger the ignition system. There are two basic types: magnetic and hall effect. The sensor reads notches in a ring mounted on the crankshaft, harmonic balancer or flywheel. See Crankshaft Position Sensors.

CROSS CAMBER
The difference side-to-side between camber settings. More than half a degree difference may cause a steering pull toward the side with the most (positive) camber. See Wheel Alignment and Alignment Diagnosis.

CROSS CASTER
The difference side-to-side between caster settings. More than half a degree difference may cause a steering pull toward the side the least (negative) caster. Caster on the left front wheel is sometimes decreased to compensate for high road crown. See Wheel Alignment and Alignment Diagnosis.

CROSS COUNTS
Refers to the switching activity of the oxygen sensor as it switches back and forth from rich to lean and back again. Low cross count activity in an upstream oxygen sensor on a warm engine indicates a bad oxygen sensor.

CROSSMEMBER
A structural component that bolts between the frame rails or attaches to the subframe of a unibody. The lower control arms may be attached to the crossmember. The position of the crossmember is important because it affects camber, caster and setback.

CYCLING CLUTCH ORIFICE TUBE (CCOT)
A refrigerant system in which a fixed displacement compressor is engaged and disengaged to maintain the refrigeration cycle. By cycling the compressor clutch on and off, the cooling output of the system is regulated.

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AUTOMOTIVE TECHNICAL TERMS B

BACKFIRE
This is the popping or banging sound sometimes heard in the exhaust when decelerating. It can indicate a problem such as over-rich carburetion, a bad exhaust valve or an ignition problem (retarded timing or a cracked distributor cap). If the backfiring occurs through the carburetor, it may mean over-advanced timing, a bad intake valve or a cracked distributor cap.

BACK PRESSURE
This is the pressure that backs up in the exhaust system as a result of the restriction caused by the muffler, catalytic converter and tailpipe. The faster you drive and/or the greater the load on the engine, the higher the back pressure in the exhaust system. Back pressure inhibits the exit of exhaust gases so the engine has to work harder to push the exhaust out. This cuts down on engine power and fuel economy. Some of the causes of high back pressure include a clogged converter, a damaged or collapsed exhaust pipe or a restrictive muffler.

BACK PRESSURE EGR
Some emissions control systems use a back-pressure sensor or diaphragm to monitor backpressure so that exhaust gas recirculation (EGR) flow can be increased when the engine is under maximum load (and producing maximum back pressure). See EGR.

BACKSPACING
The distance from the back edge of a wheel rim to the back of the center section.

BALL JOINT
A flexible coupling in a vehicle's suspension that connects the control arm to the steering knuckle. A ball joint is so named because of its ball-and-socket construction. Some are designed to never require grease while others should be lubed every six months. As the joint wears, it becomes loose. The result is suspension noise and wheel misalignment. See Ball Joints.

BAROMETRIC PRESSURE
The pressure exerted by the weight of the earth's atmosphere, equal to one bar, 100 kilopascals, or 14.7 psi (often rounded off to 15 psi) at sea level. Barometric pressure changes with the weather and with altitude. Since it affects the density of the air entering the engine and ultimately the air/fuel ratio, some computerized emissions control systems use a barometric pressure sensor so that the spark advance and EGR flow can be regulated to control emissions more precisely.

BAROMETRIC PRESSURE SENSOR
A device that senses barometric pressure for the engine control system. May be combined with a Manifold Absolute Pressure (MAP) sensor.

BATTERY
The battery is a storehouse of electrical energy for starting the engine. All cars and light trucks today have a 12-volt battery. Most are also maintenance-free, meaning you do not have to add water to them periodically. Some even have built-in charge indicators to tell you if they need charging. A green dot in the window means the battery is at least 75% charged, no dot means it needs recharging, and a clear or yellow window means you need a new battery because the water level inside is low. Do NOT try to jump start or charge such a battery. You might be able to salvage the battery if you can pry the sealed caps open and add water, but usually the battery must be replaced. Batteries are rated according to their Cold Cranking Amp (CCA) capacity. As a rule of thumb, an engine needs a minimum of one CCA for every cubic inch of displacement, and preferably two. The higher the CCA rating of the battery, the better. A typical passenger car battery might be rated at 500 CCA or higher. See Battery Testing, and Battery Jump Starting.

BLOWBY
A condition where combustion gases literally blow around the piston rings. When air and fuel are ignited inside the combustion chamber, the resulting explosion creates tremendous heat and pressure. The piston rings are supposed to seal against the cylinder walls to prevent the hot gases from escaping. But every engine suffers a small amount of blowby anyway. If the rings and cylinders are worn, blowby can be a real problem. The gases are mostly water vapor and unburned fuel, so when they enter the crankcase they contaminate the oil. Most of the gases are sucked out through the crankcase ventilation system (See PCV Valve) before they can do much damage. But in an engine with a lot of wear, excessive blowby can lead to rapid sludge buildup.

BODY ROLL
The leaning or tipping of a vehicle's body to one side when turning sharply. This reduces traction and increases tire scuff due to undesirable alignment changes. Body roll is controlled primarily by a sway bar, but the stiffness of the springs and shocks also play a role.

BOOTS
Also called bellows, these are the protective rubber (synthetic or natural) or hard plastic (usually Hytrel) covers that surround CV joints. The boot's job is to keep grease in and dirt and water out. Split, torn or otherwise damaged boots should be replaced immediately. Old boots should never be reused when servicing a joint. Always install new boots.

BRAKE BLEEDING
This is the process of removing air bubbles from the brake system by pumping fluid through the lines. Air bubbles are bad because they compress when pressure is applied resulting in a low or spongy feeling pedal. The correct procedure for bleeding the brakes on most RWD vehicles is to start at the furthest wheel. Do the right rear then left rear brake, followed by the right front and left front brakes. On a FWD vehicle with a diagonally-split brake system, do the right rear then left front brake, followed by the left rear and right front brake. See Bleeding Brakes.

BRAKE CALIPERS
The part of the disc brake that squeezes a pair of brake pads against the rotor. A caliper is nothing more than a casting with a piston inside. When hydraulic pressure pushes the piston out, it forces the brake pads against both sides of the rotor. Some calipers are "floating" in that they slide back and forth and self-center over the rotor. Others are said to be "fixed" because they do not move in and out. See Loaded Brake Calipers.

BRAKE DRUMS
The cast iron housing and friction surface around a drum brake. The brake shoes expand outward and rub against the inside surface of the drums when the brakes are applied. Worn drums often take on a grooved appearance. The inner surface should be turned smooth on a brake lathe when the shoes are replaced. If the drum has worn too thin, is cracked, warped or has taken on a bell-mouthed shape, it must be replaced. The spring around the outside of the drum on some vehicles is there to soak up vibrations and noise. See Drum Brake Service.

BRAKE FLUID
The brake system uses a glycol-based hydraulic fluid. The fluid is "hygroscopic," which means it tends to absorb moisture over time (never leave a can of brake fluid open for this reason). Moisture lowers the boiling point of the fluid and causes internal corrosion in the brake system. That is why the fluid should be replaced when brake repairs are made or every two years for preventive maintenance. There are several different types, based on the boiling temperature and other characteristics of the fluid. DOT 3 or DOT 4 are used in most passenger cars and light trucks. Use only the type of fluid specified by the vehicle manufacturer. Using DOT 3 in an application that calls for DOT 4 might create a safety hazard. DOT 5 brake fluid is different from DOT 3 and DOT 4 in that it is silicone-based. DOT 5 is NOT recommended for any vehicle equipped with antilock brakes - but it can provide long-lasting protection against corrosion for vehicles that are stored for long periods of time or are driven in wet environments. See Brake Fluid.

BRAKE JOB
A typical brake job includes replacing the brake linings (new disc brake pads and shoes), resurfacing the rotors and drums, adding fresh brake fluid and bleeding the system, and inspecting/replacing any other worn components (usually at extra cost). If rotors or drums are worn beyond safe limits, they can't be resurfaced and must be replaced. Leaky disc brake calipers, drum brake wheel cylinders or the master cylinder should be rebuilt or replaced. See Brake Job.

BRAKE LININGS
The friction material on disc brake pads or drum shoes. A variety of materials are used including asbestos, semi-metallic fibers, Fiberglass and Kevlar. Asbestos linings are used on most older vehicles and on the rear drum brakes. Semi-metallic linings are used on the front brakes of many front-wheel drive applications. Others may be factory equipped with ceramic-based linings. Never substitute one type of brake lining material for another. The linings rub against the rotors or drums to create friction. This produces a tremendous amount of heat. If the heat builds up faster than it can be shed, the brakes can fade (See Brake Fade). The linings are a high wear item. Front brakes, especially those on FWD vehicles, receive the most wear. Average life for front brakes ranges from 30,000 to 60,000 miles. For rear brakes, 60,000 to 100,000 miles is the norm. Linings should be replaced when worn down to the lining rivet heads, or when lining thickness is less than 1/8th inch or minimum service specifications.

BRAKE PADS
These are the linings used in the front disc brakes. They are called pads because of their flat pad-like shape. Each brake uses a pair of pads (one inner, one outer). Replacement pads are sold in two-pair sets, and are fairly easy to change (See Brake Squeal). Calipers should be inspected for leaks (See Calipers), and the rotors resurfaced to restore a smooth surface (See Brake Rotors). See Brake Pads.

BRAKE ROTORS
The flat disk-like plates that provide the friction surface in a disc brake. When hydraulic pressure is applied to the caliper, the brake pads are squeezed against both sides of the rotor producing friction and heat. Some rotors have cooling fins between both faces and are called "vented" rotors. The rotors should always be resurfaced when new pads are installed. If worn beyond safe limits, cracked or severely warped, the rotor must be replaced. See Brake Rotors.

BRAKES
The brake system uses hydraulic pressure to stop the vehicle when you step on the brake pedal. Pushing the pedal down pumps fluid from the master cylinder to the brakes at each wheel. This squeezes the brake linings against the rotors and drums, creating friction which brings the vehicle to a halt. The only maintenance the system requires is to check the fluid level periodically, and to replace the fluid every couple of years, or when brake repairs are performed. See Brake Job.

BRAKE SHOES
The brake linings used in drum brakes (the rear brakes on most cars). Each drum contains two shoes (a primary or leading shoe, and a secondary or trailing shoe). Replacement shoes are sold in sets of four, one pair for each brake. When shoes are replaced, the condition of the mounting hardware and return springs should be carefully inspected. Replace any worn, damaged or stretched components. Drums should also be turned on a lathe to restore a smooth surface. See Drum Brake Service.

BRAKE SQUEAL
The annoying high pitched screech that�s sometimes heard when braking. A common ailment on many disc brake-equipped cars, it is caused by vibration between the brake pad and rotor. It causes no harm, but metallic scraping sounds should be investigated because it usually means the brake linings are worn down to their metal backing plates. If not replaced, the metal-to-metal contact can ruin the rotors or drums. Brake squeal can be eliminated by installing shims on the backs of brake pads, by applying anti-squeal compound or a moly-based brake grease never ordinary chassis grease) to the backs of the pads, and/or resurfacing the rotors. Applying a nondirectional swirl finish on the rotors can provided added noise suppression. See Brake Noise.

BTU
Abbreviation for British Thermal Units. One BTU is the amount of heat it takes to heat one pound of water one degree Fahrenheit. The energy value of various fuels is often expressed in so many BTUs per gallon. Gasoline, for example, has around 120,000 BTUs per gallon.

BUMP STEER

The tendency of a vehicle to suddenly veer or swerve to one side when hitting a bump or dip in the road. The condition is caused by uneven toe changes that occur as a result of the steering linkage or rack not being parallel with the road surface. This causes the wheels to change toe unevenly as the suspension undergoes jounce and rebound.

BUMP STOPS
Rubber bumpers (often cone or wedge shaped) on the chassis that limit suspension travel. "Bottoming out" the suspension means hitting the bump stops.

BUSHINGS
A liner, grommet or sleeve made of rubber, plastic or metal that fits around a bolt or bar to support, position and in some instances cushion the part. Bushings are used around the pivot bolts that attach the control arms to the chassis. They are also used around sway bars, the links that connect the ends of the sway bar to the control arms, and on the ends of strut rods. Rubber or soft elastomer bushings provide "compliance" in the suspension to help dampen road noise, vibrations and feedback. Hard plastic (usually polyurethane) bushings "firm" up the suspension for improved handling but also increase ride harshness.

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