Poor running 90Q

[DePenning, Charles [EPM/MTN]]

Well, I've really wanted to avoid changing the static mixture, because of
the fact that the problem cropped up almost instantly- on the highway at 65
mph.  Something broke or shifted quickly, and I thought that compensating by
adjusting the mixture screw would just cover up the problem, not solve it.
Yes, the mixture is way off (as measured in the DPR drive current and also
O2 sensor voltage, and observed in smoky/sooty, fuel smelling exhaust) but I
think it is due to a step change in the control system, not a gradual change
due to part wear or misadjustment.  
I did check the temp sensor on top of the coolant neck- both of them (within
the same sensor package), and both were within spec at ice water and boiling
water temps.
I'm starting to think that the problem may lie in either the fuel
distributor or the ECU- a failure of a component in either of these units
could lead to a sudden change in mixture control, both in open and closed
loop conditions.
Anybody have a spare '89 90Q ECU they would be willing to lend me?

Thanks!
Charley

 
-----Original Message-----
From: Huw Powell [mailto:audi at humanspeakers.com] 
Sent: Thursday, August 26, 2004 11:49 PM
To: DePenning, Charles [EPM/MTN]
Cc: 'David at icallshotgun.com'; 'quattro at audifans.com'
Subject: Re: Poor running 90Q


> Please let me know what you find out- I have been battling this 
> problem with my '89 90q for quite a few months now.  I've really 
> gotten into everything pretty well- measured all fuel pressures, DPR 
> current, OXS voltage, exhaust and intake paths, vacuum leaks, replaced 
> injectors, cap, rotor, wires & plugs, coil checked and then replaced 
> anyway, cleaned up all grounds I could find, and the bastard still 
> won't run.  It seems like it is running pig
> rich- really stinks up the garage, smoky, and the DPR current when in 
> closed loop runs to full lean signal.  And no, the cold start injector 
> isn't running more than it should.  My symptoms are exactly as you 
> describe- stumbles when idling, no power under load, revs like it is 
> missing.  Once it really warms up it eventually dies.  Last night I had
another of many 'a-ha'
> moments and thought that the crankcase vent hose might be the culprit- 
> it looked pretty collapsed, but upon replacing it, no dice.  I'd 
> really like to get this thing out on the road again, so if you (or 
> anybody else out there) has any ideas, PLEASE let me know- I'm almost 
> to the point of having it towed, and that would hurt my ego for years to
come.

You are checking the DPR current and OXS voltage, but they are not right.
Have you tried adjusting the static mixture to see if it is simply wa-a-a-ay
off?  Turn that little 3mm hex screw thing counter-clockwise to lean it out.
It might take several turns - which is a radical amount.

Your temp sender might be bad, too (on the top of the radiator hose flang on
the head), and telling the ECU that it is minus 50 degrees all the time.

Your fuel distributor could also be pooked, in which case a used replacement
is probably the best solution.

--
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/