From: bernie@metapro.DIALix.oz.au (Bernd Felsche)
Subject: Re: Audi fuel pump II??
Organization: MetaPro Systems, Perth, Western Australia
Date: Sun, 26 Jul 92 08:56:19 GMT

In <1992Jul24.151835.10540@exu.ericsson.se>
   lmcstst@noah.ericsson.se (Stamos Stamos) writes:

>The saga continues:

>I have done all the checks, relay, ground wires, changed spark plugs.
>I checked the fuel flow, I have fuel flow all the way to the fuel
>distributor. I removed a injector connection from the distributor and
>tried to start it, but no fuel came out of the distributor.
>I then removed the distributor and found the plunger to be very stiff.

>The air flow plate would have a hard time pushing the plunger.
>When I completely removed the fuel distributor and all the fuel ran
>out of it, the plunger was freed. It seemed the plunger was
>'pressure locked'. I reconnected every thing and low and behold the
>engine started. It was running fine, but the fuel pump was making 
>much more noise than it used too. The engine then died, ran for about
>a minute. I didn't disconnect the fuel distributor again but I assume
>the plunger had become 'pressure locked' again. Some how the fuel 
>after the plunger would get locked in and the air flow sensor would
>be unable to push the plunger.

From your description, it could well be the control pressure
regulation circuit. This acts on the top of the plunger to
"fine-tune" the plunger stiffness against the metering plate
lever.

There is a small piston in the side of the fuel distributor
which does the actual regulation. Connected to it, is a line
to the control pressure regulator, mounted on the engine
block. This is also called a cold-start regulator, though it
does a lot more than that.

Disconnect the fuel line to the control pressure regulator
(careful, lots of fuel) and see if the plunger moves easily.
If it does, then you probably have a faulty control pressure
regulator -- or maybe just a clogged fuel return line.

If the plunger does not move freely, then the control piston
(or push valve) is stuck. You'll have to dismantle that
section of the distributor to see the cause, but be very
careful with the parts... This would be about the last thing
to go wrong. A stuck regulator can mean replacing the fuel
distributor. It's not very likely that it is broken because
you got it moving after venting pressure.

A little more likely, is that the control pressure regulator
on the side of the engine has failed in a strange way,
causing the control pressure to be too high.

>The specs for the pump say it should take 8.5 amp at 11.5v.
>As my digi-meter only goes to 10amp I didn't want to connect it to 
>measure the amps. I measured the pump resistance instead.
>It was about .9 ohms, that gives 12.8 amps at 11.5v .
>I wonder how accurate this is? Does the internal resistance of a DC
>motor change when it is working??

Actually, the current draw depends on the pump load
(pressure and internal friction) so simply measuring the
winding resistance is not sufficient. If you don't want to
burn your multi-meter (most will take more than 20 amps even
though they only claim 10 amps), then put a small resistance
in the fuse position, and measure the voltage drop. (I trust
I don't have to tell you how to select a resistor.)

>From all of this I diagnose that the fuel pump failed, 
>over pressurising the fuel distributor.
>Do people agree/disagree with this???

I do. The fuel pump, if it is really dead, failed as a result
of an over-pressure condition. The fuel pump has probably
shut itself down and will work when the problem is
rectified.

>If this is the case, did the increased fuel pressure from the pump
>break the fuel pressure regulator in the fuel distributor? The
>distributor also contains pressure regulators for each injector.
>I am not convinced that the fuel pressure regulators in the distributor
>are broken as the engine 'seemed' to run 'ok' for a minute, before the
>fuel build up in the distributor stopped the engine.

If the engine always restarts after venting fuel pressure,
then it's the pressure regulation circuit. Probably -- a
faulty return line. Maybe something hit it and caused it to
be closed or partially restricted.

Get a large clean container and disconnect the fuel return
line(s?) and allow them to drain into the container (you'll
probably want to tie them down unless you're an octopus).
Try to start the engine again.

If the engine runs with return flow to the containers, then
fix the return line under the car (and send me 200 chocolate
frogs;-))

Let us know how you go...
-- 
+-----+ Bernd Felsche                     _--_|\  #include <std/disclaimer.h>
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