Verdict: Fuel Pump

Marc Boucher mboucher70 at
Fri Feb 6 13:25:12 EST 2004

Its now quite definitive.  The problem is the fuel pump.  Likely there is no
problem with the fuel distributor or any related items up front.  Today's

1.) put the fuel pressure regulator back in place.  Retested flow as before
using long thin gauge wire.  Same result.  Pump bogged down before it could
build enough power.

2.) retested with shorter, thicker wire that I'd used before. Pump didn't
bog down and proceeded to produce a steady flow of 250ml in 30 seconds from
the return.

In general it appears that the pump operates in two modes: In the first mode
it makes the sound of a high pitched electrical motor running fast.  In this
mode it will produce a steady stream through the return valve of 250 ml in
30 seconds, and also up through the fuel distributor (if plate is lifted).

The other mode ...occurs most often when conditions are other than
ideal...e.g. the voltage encountered during cranking.  Here the fuel pump
motor makes a different sound as though its laboring.  The flow from the
return line is not barely builds up enough pressure to fire
through the pressure regulator momentarily and then closes.

When the pump is making the high pitched noise, its pumping enough to start
and run the car.  I managed to do this...running on all 5 cylinders, the
DPR, ISV, etc all doing their thing.  In all cases, when it stalled, the
fuel pump had gone back to its other (low rumbling) sound.

So I'll change the pump.
(written last night).

Today I got in touch with a local member of the Audi group.  His experience
was that the large amount of wiring from the pump to the relay up front to
the battery had caused in his case enough voltage drop to hinder his fuel
pump and he solved the problem vial a relay near the battery that got the
pump fuel power via a more direct route.  I'm going to attempt to measure
pump voltages, resistance, etc.. but still think I'll end up replacing the soon as I can figure out which one it uses.

I idled the car for about 15 minutes yesterday...interestingly the 'check
engine' light was on the whole time...will pull the codes today...should be
interesting.  I'm wondering if all this testing, attempted starting, etc
could have damaged the oxygen sensor.  Its sure fouled the plugs and given
the starter a new noise.  Its also killed the battery at least once.  I put
it on trickle charge and the electrolyte measures in the green a few days
after charging.


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