Barely-running '89 90q

[DePenning, Charles [EPM/MTN]]

Thanks for the guidance Huw.  Unfortunately nothing seems to be
malfunctioning- I must be still missing the gremlin, or he is quick and
invisible.  Temp sender good according to Bentley specs, fuel dist. pot good
(I knew that 3 wire harness connector from the junkyard would come in handy
someday!), both WOT and idle switches work as expected, dpr current measures
good (100 mA w/o engine running, down to 10 mA for the 'functionality' test
when the WOT switch is closed and the engine is stationary, varying current
with engine running, tracks with O2 sensor installed, steady with it
unplugged and grounded), O2 is all over the place, but unplugging does not
remedy the situation.  CSV ok, unplugged it with no change, grounds good and
air filter clean.  WTF?  
Is it possible to send a steady 0.7v to the computer in place of the O2
sensor voltage (fake it out)?  Is it possible that a crappy fuel pump could
pass pressure and delivery tests but still not work under running
conditions?  Is it possible that I am losing patience with die
schiessensewagen?   (I probably just called myself a jelly doughnut or
something in German... )

Charley 


-----Original Message-----
From: Huw Powell [mailto:audi at humanspeakers.com] 
Sent: Tuesday, March 30, 2004 5:48 PM
To: DePenning, Charles [EPM/MTN]
Cc: 'quattro at audifans.com'
Subject: Re: Barely-running '89 90q

> Well this has really turned into a stumper.  Some of you may recall 
> the problem I'm having with my 221k mile '89 90q- in short, it runs 
> like it is missing on at least one if not two cylinders.  Starts like 
> crap, runs like crap when warmed up. This behavior started suddenly at 
> highway speed, with no indication of this before.  No power, and the
exhaust smells pretty rich.
> Here's what I have done:
> Checked spark- OK
> Checked compression- OK
> Checked TDC on cam compared to flywheel- OK Checked fuel system 
> pressure(s)- OK Checked fuel pump delivery rate- OK Checked O2 sensor 
> operation-at least attempts closed-loop Checked cat- not plugged, but 
> I hollowed it out anyway Checked for vac leak- as well as I could, 
> hoses look ok Pulled Codes- 4444 Pulled out and tested injectors- 
> thought I had it here....  But noooo.
> Still runs the same, maybe a little worse.  Argh!  I'm getting thin on 
> ideas now.  Would a big vac leak cause this behavior?  I am just 
> baffled by the fact that it ran great for a good long while and then
suddenly crapped out.

Other than obvious physical issues like vacuum leaks, what you need to do is
check and verify all the senders and mechanicals of the CIS-E3 system.  One
at a time, and don't worry if a given component could cause the problem,
check it anyway.

People have mentioned the temp sender - on top of the upper coolant flange.
best way to test is to remove it, bring it inside, and immerse in boiling
and iced water, measure resistance.  Compare to Bentley manual spec.

Potentiometer - on the "hidden" side of the fuel dist.  Tough to get to, I
made a little 3 pin out jumper to get to mine.  measure while slowly raising
air plate, should be a smooth change in resistance with no dropouts.

WOT and idle switches - connector near throttle body, check to make sure
they open and close properly.

Pressure actuator - on front of fuel dist, little grey box with a connector.
measure current, when at warm idle it should be near 0 mA. 
When cold it is higher, 50-100 mA or so and dropping as the engine warms up.
The ECU controls this when cold based on the temp sender, when warm based on
OXS signal ("closed loop").

OXS output - hard to measure if other things are driving the system rich,
but if it the problem, disconnecting it should pretty much remedy the issue.

Uh, what else?  ISV couldn't cause the problem, but no harm in cleaning it
anyway.  Check its duty cycle when cold to warm, should start highish and
slowly drop to about 30%.  (at idle)

make sure the cold start valve is not firing all the time for some reason

you've checked your injectors and ignition.

make sure the engine fuses on the side of the fusebox are good.

make sure the ground wires to the intake manifold are intact and clean.

check your air filter.

well, that's about all off the top of my head.  I'm sure if anyone thinks of
anythig else they will chime in.

--
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/