Note. Supply voltage is normal. The remote control -VAG 1348/3A- is connected.
1. Unscrew the fuel filler cap.
2. Disconnect the fuel supply line (2), drain the escaping fuel into a clean rag.
Attention. The fuel supply line is under pressure. Cover the joint with a clean cloth before disconnecting hose connections. Then relieve the pressure by carefully disconnecting the connection.
3. Connect pressure tester -VAG 1318- with adapters -VAG 1318/23- and -VAG 1318/17- to fuel supply line.
4. Connect hose -VAG 1318/1- with adapter -VAG 1318/11- of pressure tester and hold in measuring vessel.
5. Open the stopcock of the pressure measuring device. The handle indicates the direction of flow (A).
6. Press remote control button -V AG 1348/3A-. In doing so, slowly close the shut-off valve until a pressure of 3 bar appears on the pressure gauge (0.3 MPa). Now do not change the position of the shut-off valve
7. Empty the measuring vessel.
8. The volumetric flow of the fuel pump depends on the voltage of the battery. Therefore, you should connect the multimeter with an auxiliary wire to the car battery.
9. Press the remote control button for 30 seconds while measuring the battery voltage.
10. Compare the volume flow of the fuel pump with the required value.
Countdown example:
During the test, a voltage of 12.5 V is measured on the battery. Since the voltage at the pump is approx. 2 V lower than the battery voltage, measured from the diagram Minimum pump volume flow 540 cm33/30 s.
*) Minimum volume flow in cm3/30 sec.
**) Voltage at the fuel pump with the engine stopped and the pump running (about 2 V less than battery voltage).
If the minimum volume flow is not reached
11. Check the fuel lines for possible narrowing of the cross section (too much bending) or clogging.
12. Disconnect the hose (1) fuel supply line from the fuel filter inlet, as shown in the figure below.
13. Connect pressure gauge -VAG 1318- with adapter -VAG 1318/17- to hose (1), shown in the figure below.
14. Repeat the pump displacement test.
If the minimum volumetric flow is reached
15. Replace fuel filter.
If again the minimum volume flow is not reached
16. Remove the fuel pump and check that the pump screen is not clogged.
In the event that no malfunction has been found so far
17. Replace fuel pump assembly (for details, see the relevant section in this chapter).
In the event that the volumetric flow of the fuel pump is reached, and there is still a possibility that there is a malfunction in the fuel system (for example, occasional power failures)
18. Check fuel pump current take-off as follows:
Reconnect all disconnected fuel lines
Connect the multimeter in the current measurement mode with electrical clamps to the wire from the contact (1), as shown in the figure below, the fuel pump harness connector.
Start the engine and let it run at idle speed.
Measure the current draw from the fuel pump. Required value: no more than 8 A.
Note. If the fault appears in the power system only from time to time, then the test can also be carried out in the test run code. But this requires the presence of a second mechanic.
If the current draw is exceeded
19. Replace the fuel pump.