Tài liệu học tập cơ bản khái quát về động cơ và các bộ phận trên ô tô phiên bản tiếng anh. Tài liệu này nhằm giúp chúng ta tiếp cận được cấu tạo chức năng của các bộ phận của xe. Với tài liệu này giúp các bạn sinh viên ngành cơ khí ô tô tiếp cận được những kiến thức cơ bản về ô tô và đồng thời nâng cao kiến thức tiếng anh. Bộ tài liệu này được soạn thảo bởi trường đào tạo và huấn luyện nghề ở Canada.
Chapter 34 Emission Control Diagnosis and Service Emission Control Diagnosis and Service • The quality of an engine’s exhaust depends on: – The effectiveness of the emission controls – The efficiency of the engine • The three emissions controlled are: – HC, CO, and NOx I/M 240 Test • Checks emission levels during vehicle operation • Simulates a short city drive and a longer highway drive • The results of two phases are combined • If the vehicle fails the test, it must be repaired IM240 Drive Trace Other I/M Testing Programs • Some states test emissions at idle only • Other states precondition the vehicle by running at a high idle or at 30 mph prior to testing • CARB developed the acceleration simulation mode test • The Repair Grade (RG-240) is similar to the I/M 240 test but more economical Interpreting the Results of an I/M Test • The report shows the amount of gases emitted and the cutpoint • Look at the gases, loads, and speeds when over the cutpoint • Consider correlations between gases and systems Exhaust Analyzer • Uses a sample hose in the exhaust • A four-gas analyzer measures HC, CO, CO2, and O2 • A five-gas analyzer measures NOx in addition • Limits are set by vehicle year and model, local and state laws Interpreting the Results • HC and CO are a direct indication of engine performance • High NOx readings indicate high combustion temperatures • High CO2 indicates complete combustion • O2 should be low and is inversely related to CO General Guidelines • HC is a result of incomplete combustion • High CO indicates excessively rich • When CO goes up, O2 goes down • O2 is unchanged by the catalytic converter • NOx is lowest when CO and HC are lowest • An extremely rich mixture will cause high HC, CO, and O2 EGR System Diagnosis and Service • EGR valves are calibrated for each engine • Performance can be affected by too much or too little EGR flow • Too little flow can cause engine overheating, detonation, and excessive NOx EGR System Conditions and Symptoms • EGR stuck open can cause: – Rough idle – No-start, surging, or stalling • EGR stuck closed (or system inoperative) can cause: – Detonation (spark knock) – Excessive NOX emissions – Poor fuel economy Scan Tool • EGR monitor activated by input from ECT, IAT, TP, and CKP • DPFE and vacuum regulator circuits checked for opens and shorts • Hoses are checked once per drive cycle • EGR flow checked continuously at idle • MIL on if test fails two consecutive drive cycles Scan Tool (cont’d) • Too much EGR flow on MAP systems will increase manifold pressure • Excessive EGR flow will cause negative fuel trims • Too little EGR flow will cause positive fuel trims EGR System Troubleshooting • Check engine mechanical condition, fuel and ignition systems • Sticking valves, obstructions, and loss of vacuum • Check vacuum hoses for leaks, kinks, cracks, and flexibility Exhaust Gas Temperature Sensor Diagnosis • • • • Remove and place in a container of oil Insert a thermometer and heat the oil Connect ohmmeter leads to sensor terminals Sensor should have specified resistance at various temperatures Diesel Engines • High Pressure – Capture exhaust gas before the turbo and redirects it back into intake air • Low Pressure – Collects exhaust gas after the turbo and PM filter and returns it back to the intercooler Catalytic Converter Diagnosis • Oxygen store is one convert function and is a good indicator of efficiency • OBD II systems compare oxygen content pre and post converter • Catalyst monitor runs after HO2S monitor Catalytic Converter Diagnosis (cont’d) • When the HO2S signals become alike and stay that way for a number of drive cycles, a DTC will be set • A converter DTC does not always mean the converter is faulty: – Small leak in secondary AIR system – Small misfire causing extra oxygen in exhaust – An exhaust leak downstream of the front HO2S Converter Diagnosis • Delta Temperature Test – Use a pyrometer to compare converter inlet and outlet temperatures (Outlet should be 100°F [38°C] hotter than inlet) • 02 Storage Test – Use exhaust analyzer to check 02 content (should be about 0.5 to percent) • Converter Efficiency Test – Use exhaust analyzer to check CO2 content (should be greater than 11 percent) AIR System Diagnosis and Service • Most systems are computer controlled • The AIR monitor checks the electrical circuit and the ability to inject air into the exhaust • Enable the AIR system and watch HO2S voltages – low readings indicate AIR system is operating Noise Diagnosis • Leaks from the exhaust can cause a hissing noise • The AIR pump shaft seal can cause an air leak • Rattling from the pump when running can be from worn isolator mounts System Efficiency Test • When operating correctly, HC, CO, and CO2 are decreased and O2 is increased • Run the engine at 1500 RPM with AIR enabled and note exhaust readings • Disable the AIR system and record the exhaust readings and compare .. .Emission Control Diagnosis and Service • The quality of an engine’s exhaust depends on: – The effectiveness of the emission controls – The efficiency of the engine • The three emissions controlled... off The solenoid may be closed through scan tool commands PCV System Diagnosis and Service • Service involves inspection, functional tests, and replacement of faulty parts • Fixed orifice tubes... System Diagnosis and Service • Most systems are computer controlled • The AIR monitor checks the electrical circuit and the ability to inject air into the exhaust • Enable the AIR system and watch