Audi A8 1994 Service Manual page 39

Motronic injection and ignition system (6-cylinder) - Edition 02.1999
Note:
The fuel pressure regulator regulates the fuel pressure according to the intake manifold pressure. This ensures
that the drop in pressure at the injectors remains the same throughout all engine speed and engine load ranges.
Warning!
The fuel system is pressurised. Before loosening hose connections or opening the test connection (to measure
fuel pressure), place a cloth around the connection. Then release pressure by carefully pulling off the hose or
cap.
Testing system pressure
- -> Connect pressure gauge V.A.G 1318 to supply pipe using adapters 1318/7, 1318/8 (pressure hose) and
1318/15.
- Disconnect vacuum hose between fuel pressure regulator and intake manifold at fuel pressure regulator
end; seal off end of hose.
Note:
If fuel flows out at the vacuum connection on the fuel pressure regulator during the following pressure test, fit
a new fuel pressure regulator.
- Start the engine and run at idling speed.
- Measure fuel pressure.
Specification: approx. 3.8...4.2 bar
- If fuel pressure does not match specification, fit a new fuel pressure regulator for test purposes and repeat
pressure test.
- If fuel pressure still does not match specification, check fuel pump and supply pipe for damage (e.g. pinching)
and renew if necessary.
- If pressure is higher than specification, check return pipe for damage (e.g. pinching) and renew if necessary.
Note:
During the following test, do not allow the engine to run for too long with the vacuum hose disconnected,
otherwise the increased fuel pressure will enrich the air/fuel mixture and may cause the lambda control limits
to be exceeded. This would be stored as a fault in the fault memory.
- Start the engine and run at idling speed.
- Switch off electrical consumers (air conditioner etc.).
- Re-connect vacuum hose to fuel pressure regulator and observe drop in pressure on pressure gauge.
- When the vacuum hose is re-connected the fuel pressure should drop by around 0.5 bar.
If the pressure does not change as specified, carry out the following tests:
- Check vacuum hose for cracks and other damage.
- Test vacuum hose for blockages at intake manifold.
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with respect to the correctness of information in this document. Copyright by AUDI AG.
1.11 - Checking fuel pressure regulator and holding pressure
Audi A8 1994 ➤
35