[s-cars] S4 #4 cylinder miss

[AUDIJIM at aol.com]

Hello,

The patient is a 1993 Audi S4. Lehmann modified engine (lower compression) 
and Lehmann chipped. RS2 injectors, EM and Turbo. I have a definite miss at 
cylinder #4. When the car is cold, it is running on 4 cylinders. As it gets 
warmer, it gets a little better, but I still hear and feel a miss. It's at it's 
worst when it is cold. I have not checked codes yet (VAG COM) but will tomorrow. 
Pulling the connector off cyl. #4 fuel injector makes no change in the rough 
running condition. Pulling the connectors off the other fuel injectors make the 
engine run on 3 cylinders, so it is definitely #4 cylinder that is the 
problem. I swapped injectors from #4 to #3 and #3 to #4 and the dead cylinder is 
still #4, so that eliminated the bad injector possibility. Compression test is 
good at all cylinders, that eliminated any problems with the engine. I 
back-pinned the fuel injectors with an LED test light and confirmed the injectors are 
getting and electrical signal to fire. Confirmed that fuel injectors work by 
removing fuel rail with injector still attached, and tried starting car. Equal 
spray pattern at all cylinders. I tried swapping POS with the connectors to see 
if the cylinder would change location, #4 cyl. still has a miss. Changed spark 
plugs, no change. Tried ECU from stock AAN, no change. Tried another set of 
POS and still no change. I pulled the coil packs and inserted spark plugs, 
grounded against valve cover, cranked engine and found spark at all cylinders. 
Reinstalled and I still have a miss at cylinder #4. Tomorrow I will physically 
change coils from cyl. #4 to cyl. #5 and see if the miss goes to cyl. #5. I 
followed the Audifans Knowledge (S4/S6) base about a miss in one cylinder, but it 
was only a procedure on how to prolong the life of the POS that uses 2 
channels by swapping the wire to the bad coil to the unused portion of that POS. That 
was no help. I realize that my spare parts engine (complete AAN running great 
before it was removed from totaled car) is no guaranty that my spare parts 
are fault free. The previous owner on my S4 said that the problem is new within 
two weeks or so. If anyone can help or has seen this before, I'd appreciate 
your thoughts/help. I bought this car to replace my 285,550 mile 5000TQ that 
needs a ton of work. Now I have two cars that need a ton of work. Hopefully when 
I get home after work tomorrow (4 PM EST), I'll have a lot of help from you 
guys on where to turn next.

Thanks,

Jim