Yeah the VAG COM can reveal all, once you have that we can go through the needed data blocks and find out exactly why its missing.

 

VAG COM confirmed no.5 misfire - looks like it never fires judging by the speed of the counts going up. Since then I have:

Removed coil and plug, witnessed nice bright spark.
Noticed gas on plug
Switched injector with no.4
Checked wiring between ECU and injector, and power to injector
Checked wiring between POS and ECU, POS and coil
Moved harnesses while engine was running and helper watched counts to see if they changed
Performed a leakdown on no.5 - excellent result
Vacuum test at intake manifold - very steady at idle and up 2000rpm (didn't rev beyond that since problem is present at idle)

Patience is running thin now! My best guess is a compression problem that I can't see with the leakdown. Maybe due to the slow speed that I turn the crank a slow to seat valve has a chance to seat, whereas when the engine is running it remains open. A weak valvespring may let the valve be held open by the lifter, but given enough time it can bleed down the lifter and close??

I don't have a compression tester but maybe it's time to go and get one and see if I can see a compression problem......

Is there anything VAG COM can do that I am missing? I only have a misfire fault on no.5, everything else is fine.

I really appreciate any ideas that you guys may have!!

 

The saga continues.....

Compression on cold engine (don't like running it with the misfire) is a miserable 110~120psi on no.5 and about 145 on no.6 (believed to be healthy).

Lucky for me I can see the intake lobe on no.5 under the oil filler so I moved the lobe to push on no.5 valves overnight, trying to encourage the lifters to bleed down as much a s possible. This is an effort to determine if the valve springs are too weak to fight the lifter springs.

 

I popped the head off this morning after trying my overnight bleed down of the lifters. I found a bent center intake valve on no.5. Smoking gun has been found!! Yippeee! Now if I could just remember how to screw it all back together......

Hopefully parts will be here in time to get running next weekend (properly!)

Cheers for the helpful advice!

 

Time to close this thread! New valve and no misfires. There is probably a moral of the story along the lines of 'if it looks like a valve, leaks like a valve, hisses like a valve, then it is a valve'. If I wasn't in denial I could have saved myself a lot of trouble checking everything but the valve. If the problem wasn't intermittent then I would have accepted a valve problem much sooner.

These run REALLY well on 6 cylinders! They pass inspection too!

 

WOOT! Glad to hear it finally got fixed.

 

Congrats man! Glad to hear you figured it out!