Looking for an explanation

[mboucher70 at hotmail.com]

Radek, 

Thought I'd share my experience with a failed fuel pump with you since it
may shed some light.  The fuel pump in my 1990 Audi 100 died several winters
ago.  

My pump failed in January, on one of the coldest days that year.  I'm in
Montreal, you're in Ottawa, so I know that the past two days were also very
cold.  So from my experience, and from what I've heard, a fuel pump that is
failing will often fail for the first time in extreme weather.  The lowered
output of a battery at that temperature can't help much either.

I too got my Audi started several times once it was inside the garage, which
made me doubt that the fuel pump could be bad.  

Others on the forum can chime in with a lot more knowledge of the subject.
One thing that I can advise is a test of the fuel pump.  If you have the
right equipment then you can test the pressure it produces.  Without any
equipment you can test the flow rate by disconnecting the RETURN line,
cranking  for 15 seconds, collecting the gas in a container and calculating
the flow rate.  Just be sure to take appropriate precautions if doing this
in a garage!   In my case the failing pump was delivering what seemed to be
a lot of gas but when it was actually measured it fell far below the spec.  

Do you have any idea the age of your fuel pump (years or mileage?)

MC


-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com] On
Behalf Of Radek
Sent: Sunday, January 31, 2010 10:23 PM
To: quattro at audifans.com
Subject: Looking for an explanation

Yesterday, my 18-year old son took his 1988 90Q to the track for winter
driving school - skidding, emergency braking, accident avoidance, etc.
Around noon he calls me and says "dad, I hit a cone and the car died.  The
fuel pump is not buzzing."  He checked for gasoline smell - none.  Reached
to fuel pump and checked wires - seemed ok.  Checked fuses and wiggled fuel
pump relay - nothing.  Long story short, poor lad had to come back home on a
flatbed.

Today I went to check out the car in daylight:  no visible damage underneath
(it was about 20 deg. centigrade below yesterday, so the cone could have
been pretty hard), fuel lines ok, brake lines ok, electrical connections to
fuel pump ok.  The pump did not buzz when the key was turned.  I tried
cranking the engine and it sputtered a bit but didn't start.

Because I had no helpers to push the car into the garage, I decided to use
the starter.  So I put the car into second gear, released the clutch alone
and turned the key:  the car rolled nicely into the garage, and A MIRACLE
HAPPENED.  IT STARTED!  I kept it running for a few minutes, turned it off,
then on again:  fuel pump is buzzing and car starts as if nothing ever
happened.

Is there a logical explanation to this?  For a moment I thought about an
immobilizer having been triggered by the impact of running over the cone,
but I don't think these cars have one?  Any ideas?  Is it the Audi Gods
putting the young lad to the test with his first Audi?

Radek in Ottawa
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