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

#12

I reconducted the leak down test to confirm air was escaping out the oil fill cap :frowning:
Picked up a borescope to confirm
IMG_0001 IMG_0003

CYL 3 for comparison
IMG_0006

Not sure how something like this could have happened

#13

Ouch, Is intake manifold intact? Maybe a flap went down the cylinder?

#14

Can you get us a few more pix of the bad cylinder. What cylinder was it? From the look in the pix looks like possible ring failure. Overall kinda had to tell tho.

#15

Here are several more. Almost look like it is splitting around the diameter at the top of the head near the valves like head gasket failure, but Block Tester fluid stayed blue… This is cylinder 4

IMG_0007 IMG_0008 IMG_0009 IMG_0010 IMG_0011 IMG_0012 IMG_0013 IMG_0014 IMG_0015 IMG_0016 IMG_0017 IMG_0018 IMG_0019

#16

Oh man…that sucks. Sorry this happened.