Re: Its runs, but its not happy - sickly Ur quattro

[quk@isham-research.demon.co.uk (Phil Payne)]

In message <000101be9495$a2f8b9c0$0603883e@default> "Jim Haseltine" writes:

> I took the quattro out for a run this morning while the roads were quiet. It
> appears to run ok when moving but it doesn't seem to idle properly. It revs
> very low and every so often drops down almost to a stall before the ISV
> pulls it back up. Once its warm there are alot more fumes from the exhaust
> than I'm used to seeing so I'm tending towards the thought that the mixture
> isn't right. Its always been rich at low revs but now I think that it seems
> to be richer.

Maybe.  Remember that you have a different chip in the ECU now, and the
default duty cycles used for the fuel frequency valve may be different.

Unfortunately, measuring the duty cycle is non-trivial because (as Scott
Mockry showed) the waveform is distorted by the resistive wire used in
the MB between the ECU and the frequency valve.  Essentially, you have
to measure at the ECU.  In North American cars (MC engine) Audi provides
a wire from the ECU to a diagnostic connector in the engine bay - but
because duty cycle is not used to adjust CO on the MB engine, there's
no connector.

> This is reinforced by the effect of clamping the breather pipe to the air
> meter dome - when I do this the exhaust produces a smoke-screen that James
> Bond wouldn't be ashamed of.

Of course, the colour of the smoke and its smell are important.  Black
and rich is OK, blue ...

This should be investigated first.  It sounds like you have a pretty
serious air leak somewhere.  Normally, blocking off the breathers
makes very little difference.

> I've got a long 3mm allen key (part of a
> Stromborg carb setting tool) but it won't grip on anything in the mixture
> adjustment hole, from the state of the tip of it I suspect that there's
> several years of oil/road grit/general rubbish in there.

Try pushing it quite firmly at several different orientations.  What
usually happens is that someone with too much but not enough knowledge
sticks a tool in, adjusts CO, and then revs the engine without removing
the tool.  This bends the screw, and you have to use quite a bit of
pressure to re-engage the Allen key.

> As tomorrow I have the fun job of lifting the fuel metering head out because
> I've dropped a 1/4 inch 10mm socket behind it, is the mixture adjustment
> screw easy to get to without having to dismantle the whole unit?

It isn't even easy to get to if you _do_ that.  This is a major strip.

--
 Phil Payne
 Phone: 0385 302803   Fax: 01536 723021
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