You can only poll and print out the registered faults in the workshop using the VAG 1551 device.
Attention! MPFI injection system electronic control unit (2.6L engine) remains active for another one and a half hours after the ignition is turned off. This means that a malfunction in the injection system that has appeared at this time is registered by the unit. However, there is no need to wait until an hour and a half has elapsed to, for example, check one of the sensors. The system will accordingly register the disconnection of the sensor power plug, however, such «malfunction» is a one-time use and, as mentioned above, it will be automatically deleted.
Due to the need to use special instrumentation, most checks of the fuel injection system are not available to the motorist. At the same time, the car owner can easily perform some checks on his own.
The electronic control unit cannot be checked using the instruments available to the motorist. But, as practice shows, the failure of the control unit occurs only in rare cases. Much more often sensors, valves, plugs fail. In the event of a defect in the fuel injection system, we recommend the following procedure:
1. Make sure all injection system fuses are OK (Nos. 13, 21, 27, 28 and 32).
2. Make sure the ignition system is OK.
3. Check the power supply system.
4. Check up visually a condition of components of system of injection of fuel. If the cause of the malfunction after performing the above steps has not been established, then read the list of possible malfunctions of the fuel injection system and how to eliminate them, and also contact the workshop to print out the trouble codes registered by the control unit.
Attention! Reading of registered faults is only possible if the battery has not been disconnected before. Disconnecting the battery deletes all data from the drive.
6. Check up a condition of hoses in which there is an air circulation. Check absolutely all air hoses, starting from the thick air intake sleeve and ending with the thinnest one, through which reduced pressure is supplied to the pressure reducing valve.
7. Make sure that the gaskets of the starting fuel valve, injectors, as well as the gaskets on the intake manifold mounting flanges are normal. A leak in the intake manifold leads to the entry into the system of «side» air. The amount of this air is not included in the parameters stored in the memory of the electronic control unit and leads to a malfunction of the system. Excess air leads to an uncontrolled lean air-fuel mixture. This defect is especially noticeable when the engine is idling due to fluctuations in the number of revolutions.
8. Warm up the engine and leave it to idle. At the same time, open the hood and disconnect the plug of the lambda probe.
9. Spray from an aerosol can with the so-called starting fluid (For example, «Startpilot») injection system block in the area of the flange on the intake manifold side, as well as other places of alleged leaks.
If, when applying the specified liquid to a certain part, the engine speed increases, then this is the place of air leakage.
10. Check that the connection plugs fit properly and that the pins are not broken or bent. If necessary, spray the contacts with an aerosol to improve contact conductivity. Do not bend the contacts yourself.
Injection system components - check
Assuming that one of the injectors is not working, it can be checked using a tester with a diode bulb and an ohmmeter.
11. Disconnect plugs of all atomizers.
12. Check the power supply to the injectors first. To do this, connect the tester with a control diode bulb to the contacts of the injector plug (see illustration).
13. Start the engine. The LED light should flash. Otherwise, there is no power supply to the injector or poor «weight» (-) control unit.
14. Check up resistance of atomizers, having disconnected all plugs.
15. Connect an ohmmeter to nozzle contacts. If the engine is cold, then the injector resistance should be 13.5-17 ohms. If the ohmmeter readings are outside the named data, then the nozzle must be replaced.
16. Check up density of closing of a nozzle. For this purpose remove a distributive fuel line together with atomizers.
17. Disconnect the injector plugs, but do not disconnect the fuel lines from the injectors.
18. Have a starter assistant crank the engine several times to activate the fuel pump and pressurize the system.
19. Watch the nozzles. No more than 1-2 drops of fuel should flow out of each nozzle per minute. Otherwise, replace the appropriate nozzle.
20. Check the shape of the jet of fuel injected by the nozzle and the volume of this fuel, if necessary.
21. Disconnect the plug for checking the throttle angle potentiometer.
22. Measure, using a highly sensitive ohmmeter, the resistance at the potentiometer contacts. Measurements are taken with the throttle valve in position «Idling» And «Full load». The engine must be turned off during measurements. The received data must be within the values given in the table.
23. Move the rubber collar of the intake air mass flow meter plug (vehicles with MPI fuel injection system). Do not unplug the plug (see illustration).
24. Connect a highly sensitive voltmeter to the contact connections of the plug on its back side.
25. Take measurement #1. Connect a voltmeter to pins 2 and 3 of the air mass meter plug.
26. Turn on the ignition. The voltmeter should register 12-14 V. If the received data does not match the indicated ones, then there is an open on the power supply line.
27. Check fuse no. 27, as well as the wire leading from fuse no. 27 to pin 3 of the air mass meter plug, or the wire «masses» (-) and its connection to pin 2 of the plug and the cylinder block.
28. Take measurement #2. Connect a voltmeter to pins 2 and 4.
29. Turn on the ignition. The voltmeter should register a voltage of 1.0-7.5 V. Otherwise, the mass air flow meter must be replaced.
30. Take measurement #3. Connect a voltmeter to pins 1 and 2.
31. Turn on the ignition. The voltmeter should show 0.3-1.1 V.
32. Start the engine. The voltmeter remains connected.
33. Turn off all electrical consumers of the on-board network. The radiator fan should also not be running.
34. Maintain RPM between idle and 4000 rpm. Depending on the current engine speed, the voltmeter should register readings of 1.5-3.4 V (maximum). Otherwise, replace the mass air flow meter, as it is defective.
The idle control valve for the 2.8 liter engine is located on the throttle valve on the right side. You can check the valve as follows:
35. Disconnect the idle speed stabilization valve plug and connect a highly sensitive ohmmeter to both valve contacts. The ohmmeter should show 7-11 ohms. Otherwise, the valve is defective.
36. Disconnect the idle speed stabilization valve for further checks. Do not disconnect the valve plug (see illustration).
37. Set the rotating piston of the valve inlet to the position «Open» or «Closed». Do not use a metal tool for this!
38. Turn on the ignition and watch the rotating piston. It should move and be located approximately in the center.
39. Check up ease of a course of the piston. With a sharp rotation of the removed valve, the piston should move. In addition, it should not have scuff marks and traces of abrasion.
Attention! Idle stabilization valve for 2.6 liter engines (MPFI fuel injection system) you can't shoot on your own. Otherwise, after installing the valve, it will be necessary to perform the so-called basic adjustment, which is possible only with the help of the VAG 1551 device, which only AUDI car repair shops have. In addition, if the idle speed stabilization valve plug is disconnected earlier than an hour and a half after the last engine start, the self-diagnosis system will register a valve malfunction, which in fact may not be true.
For this reason, on vehicles with an MPFI fuel injection system, you can only check the winding of the idle control valve yourself.
40. Disconnect the idle speed stabilization valve plug (see illustration).
41. Use a sensitive ohmmeter to measure the resistance of the valve on pins 1 and 4, as well as 2 and 3. If the valve is OK, then the ohmmeter should show 45-60 ohms.
Other valve checks cannot be performed by yourself.
If the engine malfunctions when it reaches a certain temperature, then the reason for this may be a defect in the coolant temperature sensor.
Attention! If the 2.6 liter engine coolant temperature sensor plug is disconnected earlier than one and a half hours after the engine was last started, the self-diagnosis system will register a sensor malfunction, which in fact may not be true.
42. Disconnect the plug of the coolant temperature sensor (see illustration).
43. Measure resistance on both contacts of the gauge by means of a highly sensitive ohmmeter. Compare the obtained data with the table of nominal values (see illustration).
The data obtained depends on the engine temperature. If they are outside the values inside the curves in the diagram, then the coolant temperature sensor must be replaced. The following data can be used as reference values: at a coolant temperature of 20°C, an ohmmeter should show a resistance of approximately 2.5 kOhm, and at a coolant temperature of 80°C, approximately 330 Ohm.
The intake air temperature sensor is only available on vehicles with a 2.6 liter engine. It is located on the right side of the engine next to the idle speed control valve and the pressure reducing valve.
Attention! If the intake air temperature sensor plug of a 2.6 liter engine is disconnected earlier than one and a half hours after the last engine start, the self-diagnosis system will register a sensor malfunction, which in fact may not be true.
44. Disconnect the intake air temperature sensor plug (see illustration).
45. Measure resistance on both contacts of the gauge by means of a highly sensitive ohmmeter. Compare the obtained data with the table of nominal values (see illustration).
The data obtained depends on the engine temperature. If they are outside the values within the curves in the diagram, the intake air temperature sensor must be replaced. The following data can be used as reference values: at a coolant temperature of 20°C (room temperature, engine cold) The ohmmeter should show a resistance of approximately 6.3 kΩ.
46. Disconnect the plug on the lambda probe power wire to test it (see illustrations 16.46 and 16.46a). A highly sensitive ohmmeter is required for measurements
47. Check the heating of the lambda probe.
48. Disconnect the probe heating plug and connect an ohmmeter to both probe contacts. The resistance of a good sensor is 3-15 ohms. If not, replace the probe.
49. Check probe. To do this, disconnect the probe plug and connect one connecting lead of an ohmmeter to the probe contact and the other to «mass» (-). With a working probe, the ohmmeter should show infinite (G) resistance. Otherwise a lambda probe replace.
50. Check the probe signal wire to the control box. To do this, disconnect the probe plug and connect one connecting wire of the voltmeter to the probe contact, and the second to «mass» (-). With a good probe, the voltmeter should show 0.35-0.45 V. Otherwise, check the wire. If the wire and its connection are normal, then replace the control unit.
To replace the lambda probe, disconnect the plugs and loosen the wire clamps.
51. Lubricate the threads of the new lambda probe with paste before installing it. Do not allow paste to get into the slots of the probe. Probe tightening torque 50 Nm.
The procedure for removing most parts related to the fuel injection system does not require detailed explanations. Additional explanations are necessary only for the removal of the intake air mass flow meter and injectors.
In order to remove the air mass flow meter, it is necessary to loosen the air intake hose clamp, disconnect the flow meter power plug and remove the upper part of the air filter together with the flow meter.
Fuel injectors - removal
52. Remove the air hose between the air filter (air flow meter) and engine.
53. Disconnect the high voltage wires and put them away from the work area.
54. Disconnect the injector plugs.
55. Disconnect the fuel distribution line from the intake manifold.
56. Remove the low air pressure hose from the fuel pressure reducing valve.
57. Remove the fuel distribution line with six nozzles by pushing it up (see illustration).
58. Disconnect the injector retaining clips and remove the injectors.
59. Replace all O-rings on all injectors and lubricate them with engine oil prior to installation.
60. Reinstall the nozzles. When installing, be careful not to wrap the sealing ring or damage it.
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