Misfire after engine install

A6 All/ S6 All
#1

So I had to pull the engine due to a massive failure. Passenger side exhaust cam spun and bent the valves on that side. I pulled the engine and had the head rebuilt. I just got the engine back in but now I have a small miss (not a dead miss) when i checked the faults no faults but i checked messureing value blocks and you can see the miss on clynder 7 & 8

I had the injectors cleaned before re installing the engine
I changed all the plugs

When i found the miss ive:
Swaped the coils to see if the miss travels
I checked the spark plug gap
I checked the compression on 6: 165 7:165 8:165

Not sure where to go from here :frowning: thanks for the help!

#2

That’s a low comp reading. Usually they are in the 180+ range. Did spinning the cam cause any issues to the system timing wise? I can’t see a cam running out and not effecting the entire system.

#3

It did but I reset the timeing and changed some tensioner and guide’s. I would think that whole bank would be missing I only see it on those clynders.

#4

Audi manual says 10 to 14 bar (145 psi to 203 psi)

#5

Looking across all of the listed and published comp test reports 90% of them are 180 or higher. 170 or less usually there is something going on.

#6

did the place that did the heads measure valve seat runout? 1 though per inch of head diameter. outside of that you will have sealing issues. What do the other cylinders read?

#7

The shop did say they would measure the seat run out as part of the rebuild. I should also mention I did not have the car really hot, I did not want to run it too much with the misfire. I could get it all the way to operating temp and run the compression test again.

#8

No work was done on the bottom end correct? Pistons all checked for cracks?

#9

No work done on bottom end. Also the failure was not on that side head. Also it has a new intake manifold.

I’m thinking about taking it out for a drive to see if it clears up some.

#10

I don’t know what your seeing. But on the S4s if you let them sit over a long time the lifters can bleed down and it can take some time for them to come back up. This bleeding down would cause misfires. If you let the car idle for about 30min or so they would clean up.

have you driven the car or let it run for a long time yet.

#11

Drove it around and the miss went away thanks for the input!

#12

Awesome glad to hear.

#13

good ol italian tuneup. Great to hear. Perhaps it were the lifters like justin said.