Help with misfire

A6 All/ S6 All
#1

Maybe someone can provide their .02

I had my engine mounts replaced yesterday for $770 ea. Drove it to the shop no issues, picked it up and now have cyl #4 misfiring

Swapped coils and plugs but it stayed on #4. Spark plug that came out of #4 was wet which makes me think no power to the coil pack

Are there individual circuits that can prevent #4 from firing ?

What else is weird is that I drove it around the shop a couple of miles before loading it in my trailer. After washing the car and driving to the store #4 started misfiring. I feel inclined to think it is something minor (loose wire / loose ground) but will start on a compression test next…

#2

Update: Tested all pins on the coil pack harness and confirmed all have proper grounding, resistance, voltage on correct pins.

Swapped coil packs and plugs again, same issue on #4 persists

Ran output tests and all injectors have same audable click sound, even #4

Guess compression test is all thats left…

#3

Compression test was 60PSI on #4 cold where as others were 110-120.

Possibly some plasrtic from the new IM broke off into the valves

Wonder if some aerosol valve cleaner would be next steps before the IM has to come off…

#4

Are you able to do a leakdown test? It is better for determining whether compression is being lost through intake, exhaust or into the crankcase.

#5

I got #4 as close to TDC as I could, air is escaping out the intake side. However I wanted to try and rotate the crank and see if I can get it closer to TDC. Where do we rotate the crank at? Only spot I see might be the alternator?

Update:
Was able to find perfect TDC for #4, ran the leakdown and the engine side only goes to 20PSI and definatly leaking on the Intake side. Suppose Ill take off the IM and see whats happenin. Might do a borescope first

#6

Unrelated question to your thread, but how do you individually test the injectors on the S6?

#7

Out of the car, on the test bench

#8

I just did an output test with VCDS and you can hear each injector ‘click’ and cycle on/off

#9

Sure, but it is only an electrical check. If it would fail electrically, there would be a code anyway. It won’t tell you if it leaks or not

#10

How do you do that in vcds?

#11

In VCDS - ENG - Output Tests