UNIT3 FUEL INJECTION SYSTEMS TEXT C Troubleshooting the EFI System PROFESSIONAL ENGLISH
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Transcript of UNIT3 FUEL INJECTION SYSTEMS TEXT C Troubleshooting the EFI System PROFESSIONAL ENGLISH
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- UNIT3 FUEL INJECTION SYSTEMS TEXT C Troubleshooting the EFI System PROFESSIONAL ENGLISH
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- UNIT 3 FUEL INJECTION SYSTEMS TEXT B Troubleshooting the EFI System Engine Condition Electrical System Intake Air Leakage Translation Techniques(3)
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- NEW WORDS troubleshoot ['tr blu:t] v. tightness ['taitnis] n. integrity [in'tegriti] n. concentrate ['k nsntreit] v. tune-up ['tju:n- p] n. tackle ['tkl] v. dipstick ['dipstik] n. canister ['knist] n. purge [p: ] n. & v. clog [kl g] v. n. faulty ['f :lti] a.
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- vent [vent] v. crankcase['krkeis] n. probe [proub] n. meter ['mi:t] v. proceed [pr'si:d] v. symptom ['simptm] n. continuity [k nti'njuiti] n. leakage ['li:ki ] n. hesitation [hezi'tein] n. surge [s: ] n.( clamp ['klmp] n. diaphragm ['daifrm] n.
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- soapy ['soupi]a. squirt ['skw:t]v. gasket ['gskit]n. styrofoam ['stairfoum]n.
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- vapor canister canister purge valve false air vacuum hose brake booster leak detector , start by +ing strange as it may sound [ ] PHRASES AND EXPRESSIONS
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- Troubleshooting the EFI System The basic function of the fuel injection system is to supply and meter the correct amount of fuel to the engine in proportion to the amount of air being drawn into the engine to achieve the optimum air-fuel mixture. Any problems with electrical connections, air intake sensing, or fuel supply will cause poor running. Any troubleshooting should begin with simple and easy checks of the tightness of system wiring and the integrity of the air intake system. Proceed from there to more involved troubleshooting. Generally, fuel injection problems fall into one of four symptom categories: cold start, cold running, warm running, and hot start. Warm running is the most basic condition. Before troubleshooting a condition in any other category, make sure that the system is working well and is properly adjusted for warm running.
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- To simplify troubleshooting, concentrate on the sensors and components that adapt fuel metering for a particular condition. For example, if the engine will not start when cold, the components responsible for cold start enrichment are most likely at fault, and should be tested first. Engine Condition The fuel injection system is set to operate on an engine that is in good operating condition. Because the fuel injection system is often the "new item", some people waste time checking it when the trouble may be with basic engine operation. It is a good idea to use the car manufacturer's shop manual to perform a tune-up, and to check the following systems before tackling the fuel injection system. 1. Ignition system. Check timing, including advance and retard control, ignition components and spark quality. 2. Electrical system. Check battery condition and connections, and alternator and voltage regulator.
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- 3. Air intake system. Check the air filter, PCV and crankcase connections, and the evaporative emission connections. A loose oil-filler cap or dipstick can lean the mixture by admitting extra air to the intake manifold through the PCV valve. The vapor canister can enrich the mixture by admitting fuel vapors into the intake manifold through the canister purge valve. 4. Fuel system. A clogged filter may reduce fuel flow. A faulty fuel filler cap or tank vent valve may create gas tank vacuum and reduce fuel flow. Be sure the car has fuel in the tank. 5. Mechanical operation. Check grade and condition of crankcase oil, compression; valve timing, and the exhaust system. Electrical System Whenever working on the wiring, take care to avoid bending any pins or connectors. Use flat pin probes if possible. Inserting the probes of a voltmeter or ohmmeter too far into a wiring connector may spread the contacts and create a new problem.
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- Relay Set and System Power A faulty relay set may prevent the fuel pump from operating, or prevent power from reaching the control unit. Remove the connector from the relay set, and with the ignition on, check for voltage at the terminals of the connector. If there is voltage, then the relay set is probably faulty, but check the continuity of the wiring to the pump and control unit. Wiring Harness, Connections and Grounds Strange as it may seem, the components of pulsed systems usually give less trouble than the wiring harnesses and connectors that link them. Even small amounts of corrosion or oxidation at the connector terminals can interfere with the small milliamp currents that signal the system to operate. This problem is compounded by the several ground paths provided to insure reliable operation. More than one owner of a "bad" control unit or component has paid for replacement when the problem was in the wiring. In many cases, cleaning connectors and grounds may solve fuel injection problems.
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- Identify all wiring connectors and ground locations using the shop manual. The ground locations should be secure and free from corrosion or grease and oil. With the ignition off, disconnect the wiring connectors, including the control unit connector, and also check them for corrosion or dirt. Simply disconnecting and reconnecting the connectors will clean up the contacts, but you can also use a contact cleaner designed for electronic components. Don't forget to check for breaks or shorts in the wiring harness. A fuel injector or temperature sensor may be good, but the wiring to the control unit may be faulty. You can check this using an ohmmeter. With the ignition off, disconnect the control unit connector and test for continuity between the component terminals and the corresponding terminals at the control unit connector. A reading of zero ohms or very close to it indicates that the wiring is fine.
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- Some electrical tests of the components can be combined with tests of the wiring harness by removing the control unit connector and then testing between the two pins that lead to a component . Intake Air Leakage Another likely cause of trouble in pulsed systems is air leaks between the air-flow sensor and the intake valves. These leaks are often called "false air" because it is air that has not been measured by the air-flow sensor. As a result, the control unit may not provide fuel to burn with the excess air, leading to a lean condition and driveability or emission problems. These are often indicated by hesitation when the engine is cold, or surging at idle. Note that on systems with adaptive control false air is rarely a problem unless the leak is very large.
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- False Air Checks If you suspect an air intake leak, there are many possible sources. The soft rubber ductwork can crack and split with age and under-hood heat. Check clamps for tightness. Don't forget the vacuum hoses to the brake booster, the fuel pressure regulator, the evaporative fuel control system, and other places, such as vacuum diaphragms in the heater system inside the car. Check the intake manifold connection to the cylinder head, fuel injector seals, the auxiliary air valve, and the EGR valve, if fitted. Check openings to the crankcase, such as the dipstick, PCV valve, and oil-filler cap for air-tight fits. Check anything downstream of the air-flow sensor that could leak air into the system.
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- Check for leaks by pressurizing the intake system with air and then spraying a leak detector on the suspected area. An air hose inserted into the fitting for the auxiliary air valve or the idle speed stabilizer can be used to apply low pressure; only about 0.3 bar (5 psi) is needed. A spray bottle of soapy water can serve as a leak detector. Block the throttle so that it's open. Any bubbles will indicate a leak. Also listen for the sound of escaping air. You may have to plug the air-flow sensor intake and the exhaust tailpipe to hold enough pressure in the system. NOTE On systems with an air-mass sensor, it is necessary to block the sensor inlet to hold any pressure in the system. A styrofoam coffee cup clamped in the air-mass sensor inlet makes a handy temporary plug.
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- An alternate leak-detection method involves squirting solvent around suspected leak locations with the engine idling. An rpm increase indicates a leak. Be sure to use an approved solvent with a high-temperature flashpoint. You can also use propane, which tends to be drawn in better than solvent. Remember though, if the engine has an idle-speed stabilizer, it will ask any rpm increase. If you can sample CO in the exhaust ahead of the catalytic converter, look for CO increase some seconds after applying the solvent as an indication of an air leak. To correct a leak, start by tightening clamps; you might have to replace the hose or ducting, or replace a gasket. Remember, it's the small intake air leaks that cause trouble, where the engine runs, but poorly. If there's a big air leak, the engine probably won't run at all.
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- Translation Techniques(3) 1.
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- 11 As a result, these systems offer the following advantages: greater power by avoiding venturi losses as in a carburetor, and by allowing the use of tuned intake runners for better torque characteristics increased fuel economy by avoiding condensation of fuel on interior walls of the intake manifold (manifold wetting)
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