[s-cars] Non S-Car: A4 Stumble

[Paul Gailus]

With a "waste spark" ignition coil that feeds two spark plugs,
it's possible to have an early breakdown from faulty insulation
on one side of the coil secondary winding but not on the other side.
So one spark plug could be misfiring and the plug on the
other side of the same coil could still be working fine.
In fact, even if one of the coil outputs is shorted to ground,
the other side should still have a nice spark.

If you have enough slack on the spark plug wires you could
exchange the wires from cylinders 5 and 3 to the coil to
see if the misfire code then moves to cylinder 3
(confirming a bad coil).
But they probably trimmed the wires too neatly for that ;-)

Paul

----- Original Message ----- 
From: Brian Powell <powellb at gmail.com>
To: <s-car-list at audifans.com>
Sent: Wednesday, January 05, 2005 3:43 PM
Subject: [s-cars] Non S-Car: A4 Stumble


> Greetings listers,
> 
> My wife's A4 (96 12v V6) is having a stumble under load problem that I
> cannot trace down. I have tried Audiworld, etc. so I will try here.
> 
> Car seems fine, idles fine, etc. Sometimes under load (accelerating
> from 2k rpm in 3rd gear) the car begins to stumble badly. It feels
> like a pre-detonation and drop back in timing; however, the gas is
> what she has always used without problem. I hooked up VAG-COM and
> sometimes an error code is logged:
> 
> 16689 - cylinder 5 misfire detected 
> p0305 - 69-00 - cylinder 2
> 
> (I'm not sure what that cylinder 2 part of the above message means).
> 
> This code does not always appear after a stumble incident (if I clear
> the code, go drive and get it stumble); however, it always comes
> eventually. I have moved the plugs around, tested the coils, plug
> wires, PSO, etc. and nothing has had an impact. This car has three
> coils and one PSO so, if the coil were the issue, I should register
> misfires on cylinder 3 also (since 5 and 3 are on the same coil).
> 
> It doesn't ever turn on the CEL, but, sometimes does enter the above
> error code. The misfire detection (as I understand it) will flip the
> code if there are any slight deviations so it is only an indicator, I
> suppose.
> 
> I have thought about poor fuel delivery, FPR, etc.; however, any of
> those issues should register misfires on other cylinders, not just 5.
> 
> Anyone have any tips or suggestions? 
> 
> -- 
> Cheers,
> Brian
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