Test prerequisite: battery is fully charged (12 volt), fine and coarse fuel filters are in perfect condition.
Checking the supply voltage
Check the fuse No. 18 of the fuel pump, if necessary, replace the fuse.
Disconnect the high voltage wire from the ignition distributor (terminal 4, center wire) and short it to ground, if necessary using an auxiliary wire with the same cross section.
Turn on the starter for a short time, the fuel pump should start audibly.
Otherwise, pull the fuel pump relay out of the relay board. The fuel pump turnip is located on the relay board in position 12 and is labeled 67 or 80.
Pin 4 relay socket with auxiliary wire (remote control) connect with positive pole (+) battery. VW workshops use the specified auxiliary wire with pushbutton switch and 8 amp fuse. If necessary, make an auxiliary wire yourself. Make sure that the sensitive contact of the relay is not damaged during connection.
If the pump is now running, check the fuel pump relay. In vehicles from 8/92 (PB, PF, 2E) perform diagnostics of the executive units (workshop work).
Otherwise, disconnect the electrical cable from the fuel level sensor and connect to both external contacts of the plug (red/yellow and brown wire) control lamp on semiconductor diodes. Turn on the remote control - the LED should light up, otherwise, find a wire break in accordance with the electrical diagram and eliminate it.
K-Jetronic: check the second fuel pump in the same way (under the bottom of the body, next to the fuel tank). Unscrew the fastening of the wires to the fuel pump, check the supply voltage with the remote control connected.
If the supply voltage is OK, replace the fuel pump.
Screw the electrical wires to the fuel pump.
Performance check
Connect a voltmeter to the fuel pump. Turn on the remote control and read the voltmeter reading. The voltage should not fall below 9 volts, otherwise charge the battery. The voltage at the fuel pump is about 2 volts less than the battery voltage.
Remove the fuel tank cap.
K-Jetronic
Disconnect the fuel return line at the connection point and direct its end into the measuring container.
Press the remote control switch for 30 seconds and then measure the amount of fuel supplied by the pump. During the specified time, the pump must deliver at least 355 cm3 fuel.
Mono-Jetronic, Mono-Motronic, Digifant, Motronic
Unscrew the fuel supply line and connect it through the connecting element to an adjustable pressure gauge (the VW workshop uses the VAG 1318 tool for this). Connect the outlet of the manometer to a hose, the other end of which is directed into the measuring container.
Open the shut-off valve of the pressure gauge completely by placing it in the appendix -A- (along the flow direction).
Switch on the remote control and at the same time slowly close the shut-off valve until the pressure gauge shows the measuring pressure.
Measurement pressure, bar
- Mono-Jetronic — 1,2
- Mono-Motronic — 1,2
- Digifant/Simos — 3
- Motronic (4-cyl., 6-cyl. from 8/95) — 3
- Motronic (6-cyl. up to 7/95) — 4
If the measurement pressure has been reached, release the remote control switch and do not change the position of the shut-off valve.
Remove fuel from measuring container.
Press the remote control switch for 30 seconds and then compare the amount of fuel supplied by the pump with the prescribed values from the tables.
Mono-Jetronic
Mono-Motronic
Digifant, Motronic
A - pump performance of the Digifant / Motronic system.
B - different pump performance of a 6-cylinder engine from 8/95.
Attention: If the supply voltage is OK and the pump performance is too low, then proceed as follows:
Disconnect the fuel supply hose from the fuel filter inlet, connect a measuring device to the hose and repeat the test. If the minimum required pump flow is now reached, replace the fuel filter.
Remove the fuel supply unit and check the filter mesh for contamination, clean the mesh if necessary. Check fuel pump load current at idle. The prescribed value of the load current is a maximum of 8 amperes. If the prescribed value is exceeded, replace the fuel supply unit.
If no fault is found, replace the fuel pump.
Fuel pump replacement
The fuel pump is located together with the fuel level sensor in the fuel tank. Remove the fuel pump, see section «Removal and installation of the fuel level sensor» in chapter «Supply system».
Attention: The K-Jetronic system has an additional fuel pump under the floor pan next to the fuel tank.
Connect the high voltage wire to the ignition distributor.
Connect fuel lines.
Screw on the fuel tank cap.
After replacing the pump, it is recommended to check the non-return valve and the tightness of the supply system by measuring the supply pressure.
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