Next chapter: Misfiring & too rich---exhaust valve?

[cparke]

RE: 1998 Audi A4 2.8L - AHA

Ok, everything was going fine with my car running at -10.2 multiplicative trim on bank 1 until I suddenly got misfires on two cylinders (1 & 6, across from each other on the coil) and a flashing CEL last weekend. Ok, the coil, wires, and plugs are only 4 months old. Changed the coil under warranty. No more misfiring on 1 & 6, however, bank 1 still rich but not too rich and if I rev engine while in idle, I can make cylinder 1 misfire repeatedly (if I do it long enough, guess a CEL would come up after 30), but no real misfiring being detected while driving. I have to believe that intermittent misfiring on cyl. 1 over 4 months weakened the coil, and if I don't fix this, it will happen again! Changed the fuel injector on Cyl. 1, swapped 2 & 3 with 5 & 6 (so bank 1 has entirely different injectors now). Some improvement in the fuel trim on bank 1, no noticeable increase in richness on bank 2.

I have to believe the misfiring on cyl. 1 and the too rich condition on bank 1 are related, say the exhaust valve or a valve seal? My theory goes, as I weakly understand these things, at idle speeds it causes misfiring on the cylinder because some of the exhaust gas is staying in the cylinder or something like that? At multiplicative, however, some of the air-fuel mixture is going out the exhaust and the O2 sensor thinks the system is running rich. Computer is pulling back fuel, causing the whole bank 1 to actually run lean. Sound plausible?

Now, if this is true, what can I or should I do about this?

[SuperStuff]

RE: 1998 Audi A4 2.8L - AHA

I have to believe the misfiring on cyl. 1 and the too rich condition on bank 1 are related, say the exhaust valve or a valve seal? My theory goes, as I weakly understand these things, at idle speeds it causes misfiring on the cylinder because some of the exhaust gas is staying in the cylinder or something like that? At multiplicative, however, some of the air-fuel mixture is going out the exhaust and the O2 sensor thinks the system is running rich. Computer is pulling back fuel, causing the whole bank 1 to actually run lean. Sound plausible?

Now, if this is true, what can I or should I do about this?

That's an interesting thought about the exhaust gases staying in the cylinder 1 at idle speeds causing a misfire. I've been having a CEL every two weeks for a misfire on cylinder 1 for my '96 A4. It just so happens that the solid CEL turns on 30 seconds after start-up in the mornings at idle. The car runs fine with no hesitation so we clear the code. We've checked the spark plug & wire for cylinder 1 and they are fine. We figure it's not the coil pack since it's only cylinder 1 and not 1 & 6 at the same time. Do you think a thorough cleaning of the valve seal is what is needed?

[cparke]

That's an interesting thought about the exhaust gases staying in the cylinder 1 at idle speeds causing a misfire. I've been having a CEL every two weeks for a misfire on cylinder 1 for my '96 A4. It just so happens that the solid CEL turns on 30 seconds after start-up in the mornings at idle. The car runs fine with no hesitation so we clear the code. We've checked the spark plug & wire for cylinder 1 and they are fine. We figure it's not the coil pack since it's only cylinder 1 and not 1 & 6 at the same time. Do you think a thorough cleaning of the valve seal is what is needed?

I don't know where it is coming from, but I can almost swear to you that there is smell of some kind of exhaust coming out from under the hood when the engine is running. Is it just steam heat coming from the radiator, I don't know. Exhaust leak? Exhaust back-up? Bad valve seal? I just don't know where it is coming from or what is needed. Why are both banks affected by the too rich condition? (though bank 1 is clearly more affected than bank 2) Why does the misfire on CYL-1 only happen when reving the engine without any load on it? It is all very bizarre to me.

The last things I am doing is changing the fuel pressure regulator and trying out a different ECU (someone with the same car and a major engine breakdown has been generous enough to lend me his ECU while he is away, many blessings to him!). If the same conditions still result after that, yeah compression test, exhaust leak check, and/or valve seal are the kind of things I would look at next. Truthfully though, I'm not sure I'm in it for that long haul anymore. We are seriously considering to just trade-in the car at that point.