Fuel system diagnostic help.

[Bill Rowe]

i've only experienced a similar full ox sensor failure once on a vw
scirocco, but anything is possible.  could very well be the problem but i
like to address the simple and inexpensive stuff first, especially when it's
real cold out.  since the plug wire melted i would check the items connected
to it.  guess you can always disconnect the plug to the ox sensor and see if
it makes a difference.  often it's a lot of trial and error on these cars.
keep us informed.

-----Original Message-----
From: quattro-admin at audifans.com [mailto:quattro-admin at audifans.com]On
Behalf Of Doyt W. Echelberger
Sent: Friday, December 22, 2000 10:38 PM
To: M. Oesterwinter
Cc: quattro at audifans.com
Subject: RE: Fuel system diagnostic help.


A noisy fuel pump (yes, under the floor of the trunk) will be heard from
inside the car. It is really loud and anyone can hear it within 50 feet.

I have an 87 5ktq, and when mine did similar power-loss tricks, I went nuts
for a week trying to find the cause. Checked for vacuum leaks, ignition,
plugs, loose wires, etc. The car would lose so much power that I would pull
over to avoid being run down in traffic.

It turned out to be a failing oxygen sensor.  Replacing it totally fixed
the problem.

When the oxygen sensor fails, it does so in an overly rich mixture mode,
which makes the car burn fuel poorly and die.  I found that the car ran
pretty well when I cracked the throttle wide open in second gear. The extra
air leaned out the mixture for a moment, and the car surged ahead for about
two seconds.  If yours does this also, you have a supporting piece of
evidence pointing toward the oxygen sensor.

Your mechanic can test the oxygen sensor with a special instrument. It
should be producing a particular frequency, and as the thing fails, that
frequency moves toward zero. Mine worked for a few minutes when the engine
was started, and then slowly fell off to zero.

Let me know how it turns out.

Doyt Echelberge

 >>>>>>>>>>>>>>>>>>
At 06:50 PM 12/22/00 -0800, you wrote:
>I replaced the cap and rotor.  I was just at the store to buy a spark plug
>socket.  I will hopefully replace the plugs tonight.  I can't hear the
>fuel pump.  It is located in the gas tank, right?
>
>- Marcus


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