Engine Misfires Low RPM and Heavy Throttle

[racer2086]

Had this issue come up recently.

Best way to describe it is how you slow down for a turn, downshift to 2nd gear. As you pull out of the turn where RPM is 1500 or less and give it some gas (greater than 25%), the engine will misfire multiple times, until the RPM builds up and then everything is good.

High RPM nothing feels wrong at all with no loss of power. Same low RPM without heavy throttle, and there is no misfire. It only happens if you put your foot into it.

This is a weekend car that gets driven occasionally and had been running great before. 121k miles. I know I should have pulled codes before posting, which I will do when I return home from travelling. Hopefully someone has dealt with this already and it's an easy fix.

[Dave1027]

Are you still on the original fuel pump? Definitely post your codes.

[racer2086]

Sorry forgot to update this. Car is temporarily my daily while the E38 is down, so I need to figure this out. It's borderline scary when you go to take off and it starts misfiring.

There are no codes. My only code is for the oil level sensor, which I will replace when I'm due for the next oil change.

I'm not sure where to start other than swap the coils. I replaced the originals a couple years ago (not many miles). The originals were Bosch, the new ones are Delphi. There was nothing really wrong with the old ones...my misfiring at 2500-3000 RPM and the O2 codes at the time were cured with the well-known DME flash to the most updated software. Car ran great after that until recently. I still have the original coils, so I was going to swap them back in to see if it makes any difference, since its free and easy.

After that, my thought was to smoke test the car again to check for any vacuum leaks, since that's also free and easy. I smoke tested it back when I first got it in 2018 to check on things, and it checked out healthy.

Beyond that, I don't think the spark plugs have ever been changed. I got the car at 108k and it's now at 121k, so that would be the next thing to replace because of the mileage. (Recs on spark plugs? Bosch or NGK?)

Any other ideas throw 'em out there

[racer2086]

Can this be a Vanos problem? My vanos is getting noisy, and probably needs a rebuilt soon.

And yes, forgot to answer the question. I believe it is on the original fuel pump. But if it was a fuel pump issue, I would expect it to struggle up in the higher RPM band? This is only low RPM in higher gears.

[racer2086]

Figured I should update this. One day after getting off the highway after work, the car started missing pretty bad. Trying to get going at the green tripped the engine light because it was misfiring so bad.

I had some of my old ignition coils in the trunk because I was going to swap them back in as a test. I pulled codes this time and it read cylinder 3 misfire, so I replaced that with my one of my originals and all issues went away. One of my six brand new Delphi coils went bad within a few thousand miles. Disappointing.

[johnrando]

bummer, but glad it got solved.

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[fredo]

bummer, but glad it got solved.

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+1. Hope the other 5 coils will be ok for a long time.

[racer2086]

Hope so too. But if not, they're from fcp, so no worries about replacement.

What's interesting is that the old Delphi coils had black epoxy sealing the tops, but the new one was in a different style box and has white epoxy on it.

[Fried_Chicken]

One of my six brand new Delphi coils went bad within a few thousand miles. Disappointing.

Always Bosch for coils.

[BMWCurves]

Always Bosch for coils.

I thought people also recently had trouble with Bosch and there was some new consensus on either a different model or brand. Someone else can chime in on that