Misfire at high rpm under load

[Darel]

Pretty consistently, I have a misfire on #2. This only manifests above about 4500 rpm and only under load, like 90% or greater load (hard acceleration at 3/4 throttle or more). #2 will misfire badly under these conditions but as soon as I back out of the throttle the misfires stop and the car runs beautifully. There is no loss of fuel pressure. I am tracking all of this in VCDS. Also, I have swapped coil packs and the issue stays on #2. Carbon clean and new plugs less than a year / 10,000 miles ago.

Everything tells me it's the injector however sitting here mulling it over, is it possible I have a broken valve spring allowing the valve to float at higher rpm? What's the easiest way to check? FYI if the car isn't under load it will not misfire, even under high rpm - for instance, coasting at speed and downshifting. I have consistently held it over 6k with no misfire as long as I don't put a load on it. Again, no load or "normal" rpms and I have zero misfires across the board.

Thoughts? Don't really feel like pulling this manifold off for the third time in a year unless I am confident the injector is at fault (which I pretty much am, just exploring any other options).

Thanks,
Darel

[Darel]

Oh and when it does misfire, I get the flashing CEL indicating it's dumping fuel into the cats. It may or may not stay on when it stops flashing (it's done both).

[JLAllroad]

Take a look at the spark plug itself, outside of the coil which you moved, possibly the harness?

As for the injector.
Any fuel in the oil? Any dripping/leaking? You can check this when you pull the plug. Additionally, after driving the car and shutting it off the fuel pressure should continue to climb 2-3xs idle pressure, if it doesn’t I would suspect the injector.




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[PR.138]

A quick check would be to move both coil and spark plug away from cylinder #2. That way you can eliminate the spark plug as well. Even with it being fairly new, they can sometimes develop hairline cracks in the ceramic upper portion or get fouled from misfiring due to a weak coil.

[shortyolsen2017]

If the spring was broke you'd hear it at all rpm, I'd lean towards spark plug, coil and or wiring for that cylinder, worse case scenario could be piston ring/compression problem beginning to start. Try a compression test. Either way I wouldn't drive it until resolved.

Try new set of plugs and swap all coil locations.

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[Darel]

Put a new plug in #2 and swapped coils with a different cylinder and the miss remained exactly the same, stayed on #2. Again only at higher RPM (4.5-5K) and under hard load (hard acceleration, pedal to floor). Cylinder #2 just drops out under these circumstances.

I just want to confirm.....these cars have dual valvesprings right? Because I am thinking that this is what I'd expect if one of the two valvesprings had failed so one was enough at low RPM but once you really got a load on it the valve starts floating. Or no? Normally the first thing I'd think is injector but this is a weird way for an injector to fail. Runs just fine at low RPM and even at high ROM with no load (downshifting while maintaining speed, for example). Just this one very predictable, reproducible circumstance.

[etphonehome]

i would figure a bad or dirty injector. maybe under load it cant keep up with the duty cycle. change the injector and or run a bottle of injector cleaner through it.

[Darel]

Great, as long as we're aligned it's not a valve issue. Thanks!

[amw896]

Try the ez stuff first. I think someone mentioned it above but I would definitely try some fuel injector cleaner. I've had great success with techron when I was running a stage 2 m235i. I was getting occasional misfires when in 3rd under hard accel. I started using techron every 3k km and it went away. I know it's been beaten to death but NA fuel really is much shittier than what they get in Germany.

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[Darel]

Yeah I've been running Techron for about a week now with no change. Last time I had a bad injector, I did the Techron and it worked for about a month, then the injector stuck wide open and blew fuel out the tailpipe all the way home. Luckily I was close by.

[TristenR]

I'm having the EXACT same problem. Did you ever find a solution?

[Nick4929]

I’m having the exact same issue

[BlkS5]

Same here. New plugs, new coils, new separator, new hp fuel pump, new vacuum pump. Started smoking real bad so I ordered new injectors from ECS. What a rip off, they claimed oem for $350 but they aren’t. Started having misfires cyl 1. Moved coil, still cyl 1. Took to Audi paid $250 to diagnose but they didn’t know. Swapped injectors and it ran fine for two days then misfires cyl 4. Redid seals and runs fine until I step on it and misfires cyl 1, 2 & 4. I just ordered new injectors Bosch from Amazon for $90. We’ll see.

[Natebowen3]

Same here. New plugs, new coils, new separator, new hp fuel pump, new vacuum pump. Started smoking real bad so I ordered new injectors from ECS. What a rip off, they claimed oem for $350 but they aren’t. Started having misfires cyl 1. Moved coil, still cyl 1. Took to Audi paid $250 to diagnose but they didn’t know. Swapped injectors and it ran fine for two days then misfires cyl 4. Redid seals and runs fine until I step on it and misfires cyl 1, 2 & 4. I just ordered new injectors Bosch from Amazon for $90. We’ll see.

anyone have any updates ??