Preatorian

Ok so I have a 2001 S4 That I've been getting misfires on 3 cylinders that I can't figure out. It's always cylinder 6 tons of misfires and 2 and 3 have sporatic misfires. Here's some history. I bought the car with blown up turbos. Replaced those but there was a lot of blow by coming from the oil filler and low compression on a few cylinders and misfires so I decided to rebuild the motor. Had the heads sent out and checked and surfaced. completely rebuilt bottom end (pistons, rings, crank and rod bearings) bought a new block because mine had too many scratches in the tops that were too long and could cause compression issues. Also had the new cylinder walls honed and checked. Put it together compression tested and got 175 equally across all cylinders. Put the car back together started it up and BAM still misfires on exact same cylinders but my blow by is gone. now for the hair pulling. Started checking all the electrical systems. Checked the Injectors ohms reading normal so I moved the injectors around no change misfires don't change cylinders. Checked power to injectors no issues. Checked wiring to injectors and to coils no issues good continuity. Checked ICM's also tried switching them no change or movement. Checked coil spark, also good. Moved coil packs around, no change. New NGK spark plugs gapped to .032 also tried .028 no change. I was so pissed at this point I went back and did a compression test and was shocked to see low compression on my number 6 cylinder! completely shocked I left the cylinder open and called it a night. Went back the next day and tried the compression test again shocked again compression is back to normal! Come to find out the cylinder is getting flooded with fuel effectively washing the oil off the cylinder walls and creating my low compression scenario.

So all the history aside, How the hell do I fix this? The only thing I can think of now is replace the ECU since moving injectors around did nothing. Is it possible that part of the ECU went bad effecting fuel injector timing and duration or something? The other sucky thing is I have the J box and can't seem to find anyone selling one anywhere. Or even the AA or L. So any got any ideas for me? I have not tested the fuel pressure but seems pretty unlikely at this point. I guess I should also mention I have the tip trans. Would a ECU from a Manual car work to run the engine just to alleviate the misfire issue I know I can't drive with it but have a friend with one.

Any help is appreciated.

Preatorian

I should also mention I do have the VAG-COM and have been monitoring the car with that. although if I can change the injector timing and stuff I would have no idea how to do it.

Flyboy

How are your O2 sensor readings? A bad sensor gave me misfires.

Preatorian

All O2 senors are new and have the proper voltage and readings. I replaced those because of the massive oil saturation from the turbos being blown. probably didn't need to but figured I'd do it while I had everything out.

ECS Tuning-Audi

I'm surprised no one mentioned the ICM

A bad ICM will cause misfires try swapping them and see if the misfires move banks.

We have them available below.

Click HERE to order or for more information.


Let me know if you have any questions.

Jason

Preatorian

Yes I did check the ICM's and switched them. also checked power output to them and thru them. all was proper and functioning as it should.

Flyboy

There's a L box for sale on Audizine if you really want to go that route. I doubt it's your ECU though.

ECS Tuning-Audi

Might want to also inspect the connector boot from the coil pack to the spark plug.

Jason

Preatorian

I inspected the wires and there are some breaks in the insulation around two of the wires. So I thought they might be arching together and taped them individually with electrical tape which didn't change anything. I'm not ruling it out completely yet though and going to Audi today to get some new wires to be certain.

ur20v

That's not what he meant... He meant the boot that goes between the coil and the plug itself. Check those.

And... have you checked the tension of the intake manifold bolts? Also check your spider and F hoses.