Hi Tony and Dave,
Thanks for your advice. I will reply to both of you in one message:
On Fri, 22 Jul 2005 12:21:14 -0500, Tony >
wrote:
> Christoph Bollig wrote:
> > Hi everyone,
> >
> > My 1989 Audi 100 is not running very well and during idle id doesn't
> > sound too smooth. Especially at lower revs, the power is done and it's
> > not smooth either. It feels as if it is running only on four cylinders
> > (5 cyl engine) and sometimes it gets even worse as if only three are
> > left working. Some time ago, I pulled out HV wires during idle and it
> > is definitely cyl no 2 which is not working. However, the spark is
> > there and I exchanged the distributor cap and all HV wires with
> > another car. The problem is still there, so I concluded that it's not
> > the ignition.
>
> How does the plug look? Similar to the others?
> It could be that the balance of the I5 engine masks the effect of pulling plug
> wire on #2.
The plug looked different to all other ones, more oily. We concluded
that this was because it was not working.
When I pulled the wire on any of the other plugs, there was a clear
difference. Only on #2 there was no effect.
> > The problem was there some time ago, then went away suddenly while
> > accelerating and came back a few weeks later. Unfortunately, it
> > decided to stay with me now.
>
> Before throwing money at ignition parts you may want to consider other causes. I
> would be suspicious of engine vacuum.
>
> Test while idling:
> Pull oil dip stick up. Engine should begin running very rough.
No effect.
> Replace dip stick.
>
> Remove oil fill cap from valve cover. Engine should stall (quit)
When I open it, it feels like a vacuum is pulling the cap down.
However, when I remove it, there is no effect.
> If these do not perform this way you need to isolate and fix the vacuum leak
> before other things. The crank case breather tube is a chronic problem on the I5s.
The pipes around the engine were all replaced relatively recently.
I did the same test on another Audi with the same engine (but a bit
older, 1988 model). It was exactly the same behaviour (feels as if
vacuum under cap, but no effect when I take it off). That other Audi
is running fine with less than 10L fuel consumption per 100km.
Taking all this into account, I still believe it is a problem specific
to that cylinder. I forgot to mention that all spark plugs were
replaced, still no change. I might also be worth noting, that when the
problem went away, it went very suddenly. It was a clear transition at
which the car suddenly performed well again. Unfortunately, the
problem came back and I cannot reproduce the "get better" part again.
On Tue, 26 Jul 2005 11:48:59 GMT, "dave" > wrote:
> Compression test engine.
Do you mean a compression test? I did one a few months ago and all
cylinders were normal, except that #3 was down slightly. Can
compression come and go like this?
> Exchange that #2 plug with another plug and see if the problem is still with
> #2
As mentioned, all plugs were changed.
> Exchange injector with another.
I am a bit reluctant to pull out the injectors, after I read somewhere
on SJM Auto-Technik (
http://www.sjmautotechnik.com/ ) that some part
of the injector could fall into the cylinder and one would have to
take off the cylinder head if that happens. Not the type of thing I
want to learn at the moment :-(
> Maybe a vacuum leak from a hose or at the injector causing problem.
Do you mean a leak where the injector goes into the cylinder? Any way
I can test that?
I was wondering whether there could be a problem with the injection
pipes or somewhere in the system. Maybe some dirt clocking it up?
I was hoping there might be some simple test I could try on the
injection system. But if the diagnosis is difficult, I will just have
to face it and bring it to the experts :-(
Thanks anyway for your help,
Christoph
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