1990-93 VW Passat
The CIS-E Motronic system uses two fuel pumps. The first is a small transfer pump to get the fuel out of the tank and the second boosts the fuel pressure to the necessary amount. The transfer pump is located inside the tank and the main pressure pump can be found under the vehicle. This transfer pump is located under the rear seat and is part of the fuel gauge-sending unit. The main fuel pump can be found in the reservoir in front of the rear axle beam. There is a check valve inside this pump to maintain pressure in the lines, especially on hot days, to avoid vapor lock.
The fuel filter is mounted to the side of the reservoir. This filter has no specified replacement interval and should be good for the entire service life of the vehicle. Whenever the ignition key is in the on position, the pump should run for at least 2 seconds to pressurize the fuel lines. If the Engine Control Unit (ECM) does not see a signal from the Hall Effect sensor in the distributor it will shut the pump off. If a Hall Effect signal is present, the pump will continue to run as long as a signal is detected. It is this Hall Effect signal that signals the ECM that the engine is rotating therefore indicating that fuel is needed. The pump is operated via a relay that is controlled by the ECM. This relay is located in the vehicles fuse panel. The main contacts of the relay can be jumped to run the pump during testing.Fuel Transfer Pump
On CIS-E systems the transfer pump is mounted in the fuel tank as part of an integral assembly with the fuel gauge sender.
- Remove the rear seat and the access cover.
- Disconnect the wiring and hoses and unscrew the retaining collar.
- Carefully lift out the pump and gauge sending unit assembly.
- Disconnect the pump from the sending unit.
- Installation is the reverse order of removal.
- When installing the assembly, use a new seal.
On CIS systems the main fuel pump is located under the vehicle in front of the rear axle or in front of the tank on the right side.
- Disconnect the wiring harness connector from the fuel pump.
- Temporarily pinch off the fuel supply line from the transfer pump to the fuel reservoir.
- Place a large container beneath the fuel reservoir to catch fuel and disconnect the line from the pump and drain the reservoir.
- Remove the three mounting screws, and then remove the fuel pump from the reservoir.
- Installation is in reverse order of removal.
- Perform the following during installation:
- Replace or clean pump strainer.
- Moisten a new fuel pump O-ring with fuel.
- Use new sealing washers.
- Tighten the fuel pump-to-check valve and the fuel outlet line each to 15 ft. lbs. (20 Nm).
- Check for leaks.
1994-2000 VW Passat and 1996-2000 Audi A4
See procedure under "Electric Fuel Pump" headingFuel Transfer Pump
Testing of the transfer pump is done by measuring the delivery rate of the pump. To accomplish this test you will need a measuring container and fuel hose (max. 14 in)
- Remove the access cover to the transfer pump.
- Remove the fuel filler cap
- Bypass the fuel pump relay to operate the pump. An assistant should be available to assist with this test.
- Make a jumper wire at least 14 in long of 14-gauge wire. For safety, include an in-line fuse holder (20 amp).
- Avoid damage to the relay panel sockets. The ends of the jumper should be flat-blade connectors that are the same size as the terminals on the relay.
- With container and hose measure the fuel volume.
- Length of test. 10 seconds
- Minimum fuel quantity 10.1 fl. Oz. (300 cc)
- Reinstall components disconnected/removed for testing.
Testing of the main fuel pump is done by measuring the delivery rate of the pump. To accomplish this test you will need a measuring container and fuel hose (max. 14 in).
- Disconnect the fuel return line at the connection in the engine compartment near the right front suspension strut tower.
- Connect a voltmeter to measure the actual voltage at the fuel pump connector.
- Bypass the fuel pump relay to operate the pump.
- With container and hose measure the fuel volume. Run the test for 30 seconds and measure the fuel volume.