Audi 4000 S Quattro fuel system problem write-up.

Chris Roden chris.roden at
Wed Dec 4 22:24:34 EST 2002

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It sounds like once the fuel pressure built up in the fuel distributer, the=
 excessive pressure would not let the air flow sensor raise.  If the air fl=
ow sensor can not be raised, the engine will be essentially starved the of =
air.  The air flow sensor should be able to move easily through its entire =
range.  At least thats' my take on it.

Chris R.

-----Original Message-----
From: "Tigran Varosyan" <tigran at>
To: "'Bernard Littau'" <bernardl at>,
<quattro at>
Subject: RE: Audi 4000 S Quattro fuel system problem write-up.
Date: Wed, 4 Dec 2002 15:08:49 -0800

Let me try to explain a little more what happened. I don't know everything
about the inner workings of the differential pressures so someone can jump
in here.

What was happening is that the (NOT the DPR) MECHANICAL fuel pressure
regulator (Diaphragm Pressure regulator in the Bentley) was not letting
enough fuel leave the system. The fuel coming from the fuel pump had nowhere
to go, so pressures built up in the distributor to the max that the fuel
pump could supply (which fried my fuel pump BTW). Basically the pump was out
flowing the return rate. With pressure in the system needing to be at around
75PSI and actually likely around 130, the differential regulator could not
perform it's job. There was too much pressure on one side of the plunger,
essentially pressure-locking it.

How that works mechanically, I do not know... But that is 100% what caused
my issues.


-----Original Message-----
From: Bernard Littau [mailto:bernardl at]
Sent: Wednesday, December 04, 2002 2:58 PM
To: Tigran Varosyan; quattro at
Subject: RE: Audi 4000 S Quattro fuel system problem write-up.

> Car: 1985 Audi 4000S Quattro CIS-E Fuel Injection 5 Cyl.
> Problem:
> Fuel delivery outflows the fuel return rate. The plunger was becoming
> pressure-locked and stopped fuel delivery.

Very nice write up, Tyson!

That being said, I am having trouble with the concepts of (A) the fuel
return rate being exceeded, and (B) the plunger becoming pressure locked and
(C) high pressure causing fuel flow through the metering head to cease.

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