[urq] Ideas for rough running continued

[Ingo Rautenberg]

Thanks, Steve.  Yes, it's baffling, and the fact that my custom 3" cat back
exhaust appears to be one piece isn't making it any easier to remove from
the downpipe.  Two of the 3 nuts snapped off when I attempted removal and
the third is located at the top and ain't coming out unless I burn her off
with oxy-acetaline(don't have) or saw it off.  Air chisel didn't do any good
:-(

I did compression test early on --before "substitute with known good" and
they came out all within spec.  Gosh, I hope I'm not missing any slices from
my exhaust valves.

We'll see how good Good Friday will be for me...

Ingo
----- Original Message ----- 
From: "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>
To: "UrqList" <urq at audifans.com>
Sent: Thursday, March 24, 2005 9:51 PM
Subject: RE: [urq] Ideas for rough running continued


... I'm not thinking the cat can back up in this short an amount of
time.  I'm also skeptical on a sticky airflow meter ... I'd be
suspecting the fuel distributor, but you've already swapped that.  Seems
to me the theory of the flywheel sensors (or the Hall Sender for that
matter) doesn't fit the observation that the car will restart by messing
with the CO screw ...

When you say that you set the duty cycle to 55%, is the engine warm?
Have you monitored the control pressure to the fuel distributor and
found that it is operating within the range specified by the curve in
the IST docs/Bentley?  It almost sounds like when it dies the engine is
trying to close the loop, thinks the mixture is rich and can't crank the
lean knob down far enough.  Have you checked spark plugs and
compression?  I hate to say it, but the ECU forcing the duty cycle to
minimum sounds an awful lot like what my car was doing when I eventually
found a pie slice out of #2 exhaust valve ... the thing is that I can't
see how tweaking the CO setting on the airflow meter would have any
impact given that scenario.

... don't know if that helps much ... good luck to you Ingo!

Steve Buchholz San Jose, CA (USA)
>
> OK, fuel pressures check out - system ~90 PSI regulated after warmup
55 PSI.
> What's been replaced so far with known goods: ECU, idle valve, fuel
> distributor, warm up regulator.
> Fuel flow test 18 seconds 750 ml. Vacuum feed directly from back of IM
to ECU.
> Fuel pump jumpered to run when ignition on regardless.
>
> Ongoing symptoms:
>
> low (600-650 rpm) idle (rough)
>
> When proper duty cycle 45-55% adjustment is made (frequency valve
buzzing),
> car will make it out of the driveway (steep) and then up a
not-so-steep (10-15
> degree) incline 200 ft and then stalls and won't restart.  Fuel
pressures
> unchanged.  Roll down backwards into driveway (or not), turn CO
adjustment two
> to two and a half turns to the right and car starts (every time -- but
won't
> idle).  Still runs funny and duty cycle now 5%.
>
> So, I'm thinking replace airflow meter (have feeling it's sticking) or
does
> this also sound like it could be a clogged exhaust?  What throws me is
that I
> can consistently turn the CO screw to richen the mixture after
stalling and it
> will start (but not idle).  Still stumbles, though.  And the soot out
the back
> is black/gray.  I was thinking crank/flywheel position sensor might be
> intermittent (wouldn't that suck), but doesn't explain being able to
start the
> car when enriching mixture.  Also, have tendency to have backfires
through air
> meter...

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