Re: Audi 100 (5000 in US?), 5-cyl 10v engine troubles... Help!

[Mike Walder <miwa@premier.co.uk>]

>Check warm-up regulator and full-throttle enrichment, in that order.  The warm-
>up regulator check requires a Bosch or compatible "continuous injection" 
>pressure gauge, but a competent garage should be able to do it in 1/2 hour.  
>The full throttle enrichment issue is a bit more complicated - see if you can 
>get the appropriate Haynes manual from your local library.

By this do you mean the Thermo-time switch that controls the cold start
valve.  This has given problems in the past, and is now operated by a
switch, before the problems, it was just disconnected for several years,
without problems.  Or do you mean the Warm-up valve.  From the Haynes
manual, I can check this with a multimeter which I shall do.

>
>> The main problem seems to be associated with cylinder 4, as the plug fitted
>> here is black (i am unsure whether this is carbon or oil), as the others are
>> golden in colour.
>
>Inconclusive without a compression test.  A simple compression gauge costs
very 
>little - screw out all the plugs, earth the high-tension output from the coil, 
>screw the gauge into each cylinder in turn, and spin the engine on the starter 
>with the throttle open.  Let us know the readings.

Very interesting readings here...

With your method, of all plugs out:
Cyl     PSI     BAR
1       200     13.8
2       210     14.5
3       220     15
4       212     14.6
5       190     13

Using method from tester, with one plug out at a time:
Cyl     PSI     BAR
1       203     14
2       214     14.8
3       210     14.4
4       210     14.4
5       208     14.3

I don't understand how these are different.  The second set shows all to be
pretty matched,  but the first, not so matched.  Both are within the max
differential in the Haynes manual of 42.7PSI.  But they are all way over the
128 to 185 PSI new pressures!  How can this be?

> 
>> Also, when the engine is revved to 5000+ rpm, a cloud of grey smoke comes
>> from the tail pipe.  I was told that this was because of over fuelling, but
>> others say it may be head problems.
>
>Grey smoke, if truly grey, is indeed quite likely to be a head (or head 
>gasket) problem. Does it smell of vapourised oil, of burnt oil, or more
"acrid"?

Definately grey or whiteish (bit like a knackered turbo only less smoke),
smells of normal exhaust smoke, not particularlly oilly.  Perhaps a bit of
petrol vapour.  This only happens after being revved.  ie. when the engine
is returning to idle.  Doesn't last very long, most noticable when comming
of a motorway, to a roundabout.  Or after overtaking, which I cannot do very
well any more.  This smoke appeared before the running / acceleration problems.


I think I'd better fill you in with some more backround:

When I first got the car, I noticed that it had a tendancy to stall after
being started after a short time.  ie. going shopping.  This was overcome by
a tweeking of the idle.  Causing the engine to normally idle at 1100rpm.
This problem has never gone away.

After this, the car was becomming difficult to start, I was having to jump
start it frequently in the morning.  I bought a new battery, and this made
it easier to start, but not right.  I discovered that the cold start valve
was not connected, so I connected this up, and the car started much easier,
but would then run too rich.  I then connected this up on a switch as a
means of manual choke.

This was ok for a while, but then I started loosing power, until the engine
no longer pulled at all.  I had to take this to my local garage.  After
three weeks I eventually got the car back.  They had changed the fuel pump
with a new one, switched around the injectors, and hoses for tested second
hand ones, changed the metering pump, and Warm-up valve for second hand
ones.  He had also previously changed the sender in the distributor, the
spark plugs, the rotor arm, and cap.  This resulted in a car that went much
faster than before, and smoothly.  I was told that after getting
"specialists" to look at it, they could do no better, and the injection
system was now overfuelling, and they could give no guarantee.  This
resulted in a very fast audi!  Unfortunately this only lasted for a few
days, where the performance started to drop to normal, then below normal, to
where it is now - pretty bad.

I am now having difficulty starting from cold, it will either fire up first
turn, or after a long wait.  When it does fire, I have to keep the throttle
fully open to keep it running, and after a few seconds, it will pick up.  I
have to keep the engine at about 1500-2000rpm. until the green cold
indicator lamp goes out, before it will idle.  The cold start valve no
longer makes any difference, neither does throttle position on start up.

I hope this extra info will help.

Thanks,
========================================================================
Mike Walder                   | email:   miwa@premier.co.uk       
Computer Hardware Engineer    |          michael@dcs.rhbnc.ac.uk
Undergraduate Computer Science| WWW:     www.dcs.rhbnc.ac.uk:80/~michael
at The University of London.  | Fax:     01344 776677
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