Li3ny

Sorry to intrude on the S4 forum but the A6ers seem to have no clue of what the hell I'm talking about.

I have a 2001 A6 Stg3. The car had not been run for a few years except for being started every couple of months. Last month I decided to get it back on the road but needed to get to a long list of repairs. As far as the motor is concerned it ran fine before service, no cel's and I was aware of a developing boost leak. I did the cam end caps, tensioner seals, valve cover gaskets. Replaced plugs, air filter, fuel filter. Also repaired a few nasty exhaust leaks. It had 1/2 tank of 93 in it with Toulene for storage. After the car was back on the road and running great I filled the rest of tank with 93 Shell. The car was running very strong for the 2 or 3 rides after service. Vacuum was pinned at -30! I don't know if I've ever seen it that low. I had to drive it 50 miles so I could get it inspected figured I'd bang it all out one day, go for a cruise have some fun. But started to notice a boost leak above 21psi, also noticed my vacuum at idle was only at -15 that day upon startup..? I thought that was really odd, the day before I park the car and it's at -30. Then the next morning upon startup it's only -15? It also developed a missfire under boost that I asumed was because of the leak. I diagnosed the boost leak and replaced my drivers side intercooler. However my vacuum now is still only -15, and I still have the random missfire. Mostly on 4 and 1 but only under heavy load. I replaced all 6 coil packs but the problem seems to be worse now with crazy backfires. Car idles better than the day she was born! Only misses under heavy boost/load. Gradual boost is also OK, just no torque or it sounds like a shotgun! I logged it a few times and I am misfiring everywhere in all cylinders under load, but 4 and 1 are the worse.

Guess I'm going to pull those plugs(1&4)and check their gap. Any vacuum lines or check valves I should particularly look at? I'm going to boost check it again probably just to be safe. ICM's are pretty new.

I'm thinking with all the activity I may have cracked an old line. But it is acting almost like a stuck valve..?

Please, any input would greatly appreciated.

bgc5034

Check your fuel injector o-rings... I recently bought an 01 s4 and was having several misfires under WOT.... checked plugs, coils, switched icms, etc. next step was to check/swap the injectors... I pulled them and realized the rings were just worn to **** (loose and cracked). Just to be sure I swapped my injectors and sure enough, the o-rings i guess were not sealing properly or something..

I'd recommend trying to replace them, they're fairly cheap and extremely easy, I used a product called "Sil-Glyde" to lube them up to get them on (they don't want to be permanently lubed but need to be to slip them on and not tear them)

Li3ny

Wouldn't have thought of that one! My injectors are looking pretty crusty.

bgc5034

it is pretty rare for the injectors to fail (its not unheard of) but the o-rings will definitely wear out and will have the same symptoms as a leaky injector... (misfire)

bgc5034

Check your oil -- if they are leaking BAD it will have a gas-like smell and will be somewhat watered down (well gas'd down really lol)

ddillenger

Not after sitting for years it isn't. In fact it's very common.

Take a wooden or plastic screwdriver handle and rap the offending injectors (the metal bodies) as it's running (preferably when you're monitoring measuring blocks 15 and 16 with VCDS).

Li3ny

Swapped coil packs with no change. I was able to slow down the misfire in 1 by closing the spark plug gap. But I think that's just a band aid. I'll give that a shot tomorrow.

Li3ny

So I've checked everything else, EGT's are fine, N75 good, got my vacuum back down to 21 by replacing the crusty line to my FPR. No leaks, fuel pressure and injectors good.

I pulled my ICM's off to swap them around and noticed all the electric grease underneath was dried and crusty. I replaced them about a year ago and used the supplied grease. So I cleaned them applied new high temp stuff and swapped them. My car idled terrible. Misfires all over the place on 1,2,4 & 5. Swapped them again and the car idles perfect only misses on 1 & 4 under load. Is that weird or what? I've had one ICM completely fail on me before and the car lost a bank and would barely even idle. This is a complete mystery to me... that's why I didn't suspect them again because it was all over both of the banks... oh and also they only have 30k on them. Beru! I'll grab some new ones tomorrow.

bgc5034

Just from sitting an injector will not go bad... the rubber o-rings will absolutely wear out and crack... Injectors do go bad but age has minimal to do with it.