Memory damage
1. Multi-point injection system (MPI) equipped with a fault memory common to the fuel injection system and the ignition system. The self-monitoring procedure is described in Section 4, Chapter 12.
Lambda sensor
2. Disconnect the wire connector located behind the intake manifold (pic. 3.38) and connect the voltmeter to the two clamps in the connector.
3. Start the engine, make sure the voltage is 12 volts. If not, check the circuit.
4. If the Lambda sensor was removed from the exhaust manifold, then before installation, its threads must be coated with an appropriate paste.
System control
5. The MPI control unit includes a sequential test function to test the fuel pump relay, individual injectors, idle speed control valve and carbon filter. A special unit is required to read the fault data, so this work should be done by an Audi dealer. Since the tests were carried out with the engine not running, the action of each individual component can be heard aurally.
Coolant temperature sensor (models before 1988)
6. At a temperature of cool. fluid above 20°C, disconnect the wire pin '3' shown in fig. 3.38.
7. Connect an ohmmeter between pins 6 and 7 on the connector (pic. 3.39), the resistance should be approximately 2400 ohms. If not, check the wire contact on the sensor.
Throttle Potentiometer
8. Disconnect the wire contact from the throttle body.
9. With the ignition on, connect a voltmeter to terminals 2 and 4, then 3 and 4, in both cases the voltmeter should show 5 volts. If not, check the wiring between the yellow control box connector and the 4-pin connector.
10. To test the potentiometer, disconnect the wire connector and remove the air intake elbow.
11. Connect an ohmmeter between pins 2 and 4, the resistance should be 3500-6500 ohms. Between pins 2 and 3, the resistance should be 3000-6000 ohms. Fully open the throttle, the resistance should be 0-600 ohms.
Throttle switch
12. Disconnect the wiring and connect an ohmmeter between pins 1 and 2 on models prior to January 1989, or 3 and 4 on models from January 1989.
13. Loosen the fixing screws of the circuit breaker and adjust the position so that at the opening point of the circuit breaker, between the main screw of the installation and the stopper, a probe 0.75 mm thick enters. Tighten the screws.
Idle switch
14. Disconnect the wiring and connect an ohmmeter between the two contacts on the switch.
15. Insert a 0.5 mm feeler gauge between the main set screw and the stop. The resistance must be infinite. Pull out the dipstick and check that the throttle valve closes. The resistance must be zero.
Air volume sensor
16. Disconnect wiring from air volume sensor, connect voltmeter between pin 3 and engine ground.
17. Turn on the ignition, the voltmeter should show 12 volts. If not, check the wiring.
18. Connect a voltmeter between pins 3 and 2, the voltmeter should show 12 volts.
19. Connect a voltmeter between pins 2 and 4, the voltmeter should show 8 volts.
20. Reconnect the connector, pull back the rubber sheath.
21. Turn on the ignition and connect a voltmeter between pins 2 and 4. The voltmeter should show approximately 1.0-7.5 volts. Between pins 2 and 1, the voltage should be 0.3-1.1 volts.
22. Turn off all additional electrical equipment, start the engine and change the speed between idle and 4000 rpm. The voltage should be 1.5-3.4 volts.
Coolant temperature sensor (models since 1989)
23. Track that the engine was cooled down to the room temperature.
24. Disconnect the wiring and connect an ohmmeter between pins 1 and 2 as shown in fig. 3.41. The resistance should be approximately 2500 ohms with coolant temperature. liquids 20°C. If it is not possible to cool the engine, the resistance should be approximately 330 ohms with the coolant temp. liquids 80°C.
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