Checking the fuel injection system requires fairly complex and expensive instrumentation. For this reason, most types of system checks are beyond the power of a motorist to independently perform. At the same time, the car owner can perform some checks on his own.
The injection system control unit cannot be checked using the instruments that the motorist has at his disposal. As practice shows, the control unit is rarely the cause of engine failure. All sorts of sensors and switches cause much more problems.
1. Check that the fuses 21 and 27 of the fuel injection system are OK.
2. Check the surge protection relay on the additional relay box on the left under the dashboard.
3. Check the fuel system.
4. Examine all details of system of injection of fuel and especially a condition and fastening of fuel hoses.
5. Check the condition and tightness of all air supply hoses. If the hose leaks, additional air is drawn in, which is not taken into account by the system.
6. Inspect the connecting plugs. The sensitive contacts of the plugs must not be broken or bent. They cannot be cleaned. To increase the conductivity, spray the contacts with an aerosol compound for plug contacts.
If as a result the source of the malfunction is not found, then check the functioning of all parts of the system in order. We recommend that you go to a workshop to print out the faults recorded by the self-diagnosis system before proceeding to check the details of the system. This must be done before disconnecting the battery.
Attention! Switch off the ignition before disconnecting any injection plug. Otherwise, when the plug is disconnected, voltage peaks may occur that are dangerous for the control unit.
If the power system is not working completely, then first check the fuses No. 21 and 27, as well as the surge protection relay.
Temperature sensors
7. Disconnect the multi-pin connector of the intake air temperature sensor at the air mass meter.
8. Connect an ohmmeter to terminals 1 and 4 of the air mass meter (see illustration).
9. Disconnect a plug of the gauge of temperature of a cooling liquid.
10. Connect an ohmmeter to the contacts of the coolant temperature sensor (see illustration).
11. Disconnect the temperature sensor plug in the intake manifold. The sensor is located in the front right side of the engine compartment in the air duct of the intercooler and intake manifold.
12. Connect an ohmmeter to the sensor contacts (see illustration).
13. Disconnect the plug of a round form on a back wall of a motor compartment. This is a plug connector for the injection pump power wires.
14. Connect an ohmmeter to pins 5 and 6, through which power is supplied to the fuel temperature sensor.
15. Compare the readings of all temperature sensors obtained during measurements with the data in the diagram. The obtained values for the sensors must currently be within the wide curve on the diagram (see illustration). If so, then the sensors are OK.
Air volume flow meter (cars with a manual transmission produced before the end of 1993)
16. Release the multi-pin plug on the air mass meter by sliding the rubber collar. Do not unplug the plug (see illustration).
Numbering of contacts from right to left from 5 to 1.
17. Connect a voltmeter to pins 2 and 3 to check power.
18. Turn on the ignition and read the voltmeter reading. The nominal value is about 5 V. If this value is not reached, then there is a malfunction on the power supply line of the flowmeter from the control unit.
19. Connect a voltmeter to check the flowmeter potentiometer signal to pins 2 and 4.
20. Start the engine and read the voltmeter reading. At idle, the signal voltage should be 0.5-1.5 V.
21. Increase the number of revolutions and follow the readings of the voltmeter. The signal voltage should increase as the number of revolutions increases. The maximum value of 4.5 V is reached at the maximum engine speed. If the signal voltage of the potentiometer does not increase in proportion to the number of engine revolutions, or if it drops, then the air mass meter is faulty.
Air Mass Meter (cars produced since the end of 1993)
These measurements only apply to vehicles with automatic transmission and vehicles manufactured since the end of 1993, when the new generation fuel injection system was introduced as standard.
The air mass meter can only be checked in a workshop. A car enthusiast can only check incoming signals (see illustration 11.0).
22. Disconnect the air flow meter plug.
23. Check the voltage at the plug contacts with the ignition on (see illustration).
The table below shows the nominal values that should be obtained by measuring the voltage at the contacts of the air mass meter plug. If the values obtained are less than those indicated, then check the power wires of the control unit or the power supply to the unit.
Nozzle needle lift sensor
24. Disconnect the sensor plug on the rear wall of the engine compartment (see illustration).
25. Connect a high-precision ohmmeter to the plug contacts. The ohmmeter reading should be 90-110 ohms. If the readings obtained are outside the specified values, the injector needle height sensor must be replaced.
Engine speed and TDC sensor
26. Disconnect the sensor plug on the rear wall of the engine compartment.
27. Connect a high-precision ohmmeter to the plug contacts. The ohmmeter reading should be approximately 1 kΩ. If this is not the case, then the engine speed and TDC sensor must be replaced.
Intake manifold pressure sensor (cars manufactured before 1993)
28. Disconnect the sensor holder on the rear wall of the engine compartment on the right side to provide access to the sensor (see illustration).
29. Disconnect the intake manifold pressure sensor plug.
30. Connect a voltmeter to both side leads leading to the sensor.
3.1 Turn on the ignition and read the voltmeter. The nominal value is approximately 5 V. If the voltmeter shows a lower value, then there is a malfunction on the sensor power line from the control unit.
32. Connect the plug and move the rubber cuff covering the plug.
33. Connect the plug to the released contacts, to which the wires with brown-white and yellow-white insulation lead.
34. Start the engine and slowly increase its speed. At the same time, the voltage recorded by the voltmeter should also increase. If the voltmeter needle does not deviate, then the intake manifold pressure sensor is faulty.
Accelerator pedal position sensor
35. Remove the lining in the footwell of the driver's seat under the dashboard (see illustration).
36. Disconnect the plug of the accelerator pedal position sensor.
37. Connect a high sensitivity ohmmeter to the following sensor terminals:
- to terminals 1 and 3. The ohmmeter should show 0.8-1.4 kOhm
- to terminals 2 and 3. The ohmmeter should show 0.8-1.4 kOhm
- to terminals 4 and 3 (only cars with manual transmission until the end of 1993). The ohmmeter with the accelerator pedal released should show 0.8-1.2 kOhm, and with the fully depressed - the sign of infinity.
- to terminals 4 and 6 (only vehicles with manual transmission since late 1993 and vehicles with automatic transmission). The ohmmeter with the accelerator pedal released should show 0.8-1.2 kOhm, and with the fully depressed - the sign of infinity.
- to terminals 5 and 6 (only vehicles with automatic transmission). The ohmmeter with the accelerator pedal released should show oo Ohm, and when fully depressed - 0.8-1.2 kOhm.
If the ohmmeter readings do not match those indicated, then the accelerator pedal position sensor is defective and must be replaced.
Injection start sensor
38. Disconnect the sensor plug located on the injection pump (see illustration).
39. Connect a voltmeter to both side pins 1 and 3 (see illustration 11.38).
40. Turn on the ignition and read the voltmeter reading. Rated value is equal to battery voltage (about 12 V). If the voltmeter reading is different, then there is a malfunction on the power line from the side of the control unit.
41. Connect a highly sensitive ohmmeter to the contacts of the plug block 2 and 3. It should register 14-18 ohms. Otherwise, the fuel injection start sensor must be replaced.
Fuel regulator
42. Disconnect the round multi-pin plug on the rear wall of the engine compartment (see illustration)
43. Connect a voltmeter to pin 7 of the wire line at the control unit and «mass».
44. Turn on the ignition and read the voltmeter reading. Rated value is equal to battery voltage (about 12 V). If the voltmeter reading is different, then there is a malfunction on the power line. Check surge protection relay.
45. Connect a highly sensitive ohmmeter to the following pins of the plug block:
- pins 4 and 7 (cars with a manual transmission produced before the end of 1993);
- pins 3 and 7 (cars with a manual transmission from the end of 1993 and an automatic transmission).
In both cases, the ohmmeter should show 0.4-1.1 ohms. If the ohmmeter readings are outside the listed values, then the fuel supply regulator must be replaced.
Adjusting spool travel potentiometer. Vehicles with manual transmission produced before the end of 1993
46. Disconnect the round multi-pin plug on the rear wall of the engine compartment (see illustration 11.42).
47. Carry out the measurement 1. Connect a voltmeter to pin 2 of the («weight»).
48. Turn on the ignition and read the voltmeter reading. The nominal value is about 5 V. If the reading obtained is less, then there is a malfunction on the power line on the side of the control unit.
49. Perform the measurement 2. Connect a high sensitivity ohmmeter to pins 2 and 3 of the plug. The ohmmeter should show 1.0-3.0 kOhm.
50. Perform the measurement 3. Connect a high sensitivity ohmmeter to pins 1 and 3 of the plug. The ohmmeter should show 0.5-2.0 kOhm.
If at least one of the obtained values is less than the named ones, then the potentiometer must be replaced.
Control spool displacement sensor (cars produced since the end of 1993)
51. Disconnect the round multi-pin plug on the rear wall of the engine compartment (see illustration 11.42).
52. Carry out the measurement 1. Connect a voltmeter to pin 1 of the («weight»).
53. Turn on the ignition and read the voltmeter reading. The nominal value is about 2.5 V. If the reading obtained is less, then there is a malfunction on the power line on the side of the control unit.
54. Carry out measurement 2. Connect a voltmeter to pin 2 of the («weight»).
55. Turn on the ignition and read the voltmeter reading. The nominal value is about 2.5 V. If the reading obtained is less, then there is a malfunction on the power line on the side of the control unit.
56. Perform the measurement 3. Connect a highly sensitive ohmmeter to pins 1 and 3 of the plug. The ohmmeter should show 4.9-7.5 kOhm.
57. Perform the measurement 4. Connect a highly sensitive ohmmeter to pins 2 and 3 of the plug. The ohmmeter should show 4.9-7.5 kOhm.
If at least one of the values obtained during the last two measurements is less than the above, then the potentiometer must be replaced.
High-altitude corrector of fuel supply. Vehicles with automatic transmission and vehicles manufactured since the end of 1993 with a manual transmission The corrector itself and its readings can only be checked in a workshop. A motorist can only check the power supply to the corrector.
58. Remove facing in space for legs of the passenger party.
59. Disconnect the height corrector plug.
60. Connect a voltmeter to pins 1 and 2 of the corrector (see illustration).
61. Turn on the ignition. The voltmeter should show approximately 5 V. Otherwise, there is a malfunction on the power wire.
Fuel cut-off valve
To shut off the engine, the fuel cut-off valve shuts off the fuel supply to the injectors. If the fuel cut-off valve fails, the engine cannot be started. If the engine does not start, despite the fact that the fuel tank is full and the preheat system is normal, then a valve malfunction may be the cause.
62. First of all, make sure that the fuel cut-off valve power wire is normal.
63. Ask an assistant to turn the key in the ignition, and listen for yourself to see if the fuel cut-off valve is activated. When actuated, the valve makes a rather loud clicking sound. If there is no such sound, then the cause of the malfunction is the lack of power to the valve or in the valve itself.
64. Check the voltage supply to the valve. To do this, turn on the ignition and connect a tester with a diode bulb to the valve contact. If the light comes on, then the valve itself is faulty. Otherwise, the power supply wire is defective. Despite a valve malfunction or interruption in its power supply, the trip can be continued.
65. Disconnect the wire from the fuel cut-off valve.
66. Turn out the valve from TNVD.
67. Remove the valve piston.
68. Screw the valve body back into place to seal the system.
69. Start the engine. The start will be carried out as usual, however, the engine will need to be turned off with the gear engaged.
Checking the idle speed on TDI engines is only necessary in the event of a system defect. The electronic control unit automatically maintains the engine idle speed within 800-900 rpm.
The replacement of defective injectors, as well as the adjustment of the injection pump start, are carried out on vehicles with a TDI engine in the same way as for TD engines. TD1 motors have only different setting and adjustment values:
The check value is 0.65-0.75 mm. The adjustment value is 0.7±0.02 mm.
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