Arrrrrrrrgh! Intermittent dead 90q ignition (long)

[JShadzi at aol.com]

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[ Picked text/plain from multipart/alternative ]
I've had the same exact symptoms in the past with differen Audi's I've
owned/worked on, usually a fuel pump relay with a temp releated connection
problem.  Try jumpering the fuel pump to power next time it happens, if it
fires right up, you found the problem.

Javad

In a message dated 8/9/2002 8:12:46 AM Pacific Daylight Time,
nde264 at lulu.it.northwestern.edu writes:


> I've been having intermittent ignition problems with my 89 90q with 214000
> miles for over a month now.
>
> The symptoms/problem are as follows.  While driving the car, or more
> correctly,
> while running the car it will sometimes just lose ignition, as if someone
> had
> just turned off the key.  The tach drops to zero.  Sometimes, while
> driving,
> with the engine still turning, the car will just buck and spring back to
> life.
> This is accompanied by the tach needle bouncing.  When I do lose the car
> entirely, it will usually restart after 5 or so minutes of sitting.  The
> car
> will run very well, like nothing ever happened, for about 10 minutes and
> die
> again.  I believe that I have isolated this to the ignition system as the
> fuel
> pump does run immediately, autocheck flashes OK, etc. when turning the key
> off
> and back to the run position before trying to restart.  I just get NO
> spark.
>
> In the past month, I have replaced the distributor/hall sensor and ignition
> control computer with units sourced from Chris Semple.  Neither of these
> fixed
> the problem.  I looked through the schematic in the bentley with an
> electrician
> friend, and he told me to get what is referred to as the ignition booster
> in
> the bentley.  I bought a NEW ignition coil/module from pap-parts, and the
> car
> drove fine from Dayton to Chicago and drove fine for most of this week as
> well.
>
> I thought that this was a thermal issue as it usually happened after the
> car
> had been running for a while.  Well, yesterday, it happened while pulling
> out
> of a parking lot in which the car had sat for 3 hours.  It was still light
> outside, so I swapped out the new ignition coil/module for the old one,
> still
> no start.  I returned to the newer coil and then swapped for the old
> ignition
> computer, still no start.  I try both old computer and coil, no start.  At
> this
> point, I can smell gas coming from my exhaust.
>
> I pull a spark plug and set it on the valve cover, no spark when turning
> the
> engine.  I pull the coil->distributor wire, set it on the strut tower
> brace, no
> spark.  I then run the tests listed on pages 28-130-1 through 28-170-2 in
> the
> Bentley manual.  Everything tests fine.  The diode test on the hall sensor
> (28-160-1, first test) provided what looked to be a constantly on LED, but
> maybe the pulses were too quick for me to resolve (starter turning engine
> circa
> 300 rpm, 5 revolutions/second, therefore either 12.5 or 25 pulses/second)?
> Is
> my hall sensor fried and consistently closed circuit when hot (as it is
> effectively a transistor)?
>
> After an hour and twenty minutes of tinkering and testing, I am thoroughly
> disgusted and decide to wrap it up and call a friend for a ride home.  I
> slam
> the hood, try one more time, and as unburnt fuel fumes pour from the
> exhaust,
> it miraculously starts.  Drives beautifully for 10 minutes and stalls
> again.
> It's dark out now, and I sit in the car for 5 minutes, starts, drives home.
>
> I did not drive my car to work today, as I am afraid of it.
>
> Am I missing something?  Where else should I look?  Is it possible that the
> keyed ignition switch is failing, though it still performs all other
> functions
> it should?
>
> I'm debating wrapping up this 90q and getting another vehicle if I can't
> diagnose/fix this easily/cheaply.  I love my car, and would hate to see it
> go,
> but the rage is setting in.
>
> TIA,
>
> Nathan Engelbert
> 89 90q