[acna_pcc] Still on 4 cylinders.....No Dice!

[Mark R]

Jim, have you done a cylinder leak down test?  I understand you've ruled out
fuel injection and ignition as the problems.  If you're suspecting anything
with the mechanical workings of the cylinder (head or bottom end), this is
the first place to start.  You need shop air, and if you don't own a leak
down tester, there are several available for under $100.
This will do a few things- verify the cylinder is holding pressure (basic
compression test) and then if excess leakdown, you'll be able to test or
hear where the leaking is occurring.  For example, if it's into the colling
system, you'll see a volumetric rise or bubbles.  If it's an intake valve
not closing, you'll hear air escaping through the intake.  If it's an
exhaust valve, you'll hear air escaping through the exhaust.
Alternatively, you can use one of the chemical based fluids or smoke tests
to pinpoint the problem, but a cylinder leak down test is relatively easy
and inexpensive (presuming you have a compressor available).

Best of luck,
Mark Rosenkrantz


On 12/29/05, AUDIJIM at aol.com <AUDIJIM at aol.com> wrote:
>
> Harold,
>
> Thank you very much for your comments. But with your comments comes a few
> more questions. First, this is a 1993 Audi S4 with AAN 20 valve turbo
> engine. Why
> would the Throttle position potentiometer (G69)/Closed throttle position
> switch (F60) have anything to do with #4 cylinder? The AAN does not have
> any
> throttle adaptation other than the correct position of G69/F60. When I
> start the
> engine, I can pull the #4 connector from the injector, and NOT get any
> change in
> rough idle. If I pull any one of the other 4 cylinders, I get a change in
> rough running due to the engine now trying to run on 3 cylinders. I pull
> the #4
> injector connector only to prove that there is not any change in running
> condition. I have tested and changed nearly everything for the ignition
> and fuel
> injection systems. I thought I had this licked with the lifter change.
> They can
> be intermittent due to being under or over pumped. I have also changed the
> throttle and G69/F60 from a known good working engine (my spare AAN) That
> didn't
> help anything. I disagree with you about an intermittent piston ring or
> valve
> problem. I might have a hair line crack in a ring that gets better with
> heat/time. If I blip the throttle, it might open up and create a lower
> compression
> and then seal up again, that just a guess of course. Without pulling the
> cylinder head, I will not know what is going on with the valves or the
> pistons.
>
> Thanks again,
>
> Jim
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