1M Misfire

[Nitro158]

Hello Everyone

Wondering if anyone can help to with a misfire/stumble transitioning through 2400 RPM @ open throttle on my 1m. No codes. get 2-3 stutters and keeps accelerating. Cars done 45000km (28000mi) no mods, factory tune. 98RON fuel

The fault is intermittent as well. I've changed plugs and coils to start with. My service shop suggests injectors next. But I'd like to avoid change bit and hope solution if possible.

Reading the forums usual suspects for faults people seem to throw injectors, carbon cleans, LP and HP fuel pumps.

thanks

[PRTSB1M]

Pull the spark plugs and see if they're wet with fuel to check for leaky injectors. I've read elsewhere that puff of black smoke on cold start is also leaky injectors. A stumble from a failing HPFP would be from not enough pressure. It's a 10 year old car, and both the injectors and HPFP are known to fail; I'd recommend replacing both if they're still original. Looking at your AFR, it looks like you're getting pretty lean mixtures, especially on bank 2.

[CarJunkie]

Since you have the ability to log and monitor lambda bank 1 and lambda bank 2, it will be easy to spot leaky injectors. When you go to accelerator pedal 0, and coast in gear to maintain RPM, fuel should shut off completely and immediately. Lambda's should immediately go to 255 (max value) and stay there. If one or both banks hover around any other value, you have leaky injectors. Mine would stay around 70-100 when coasting in gear. At low rpm, it will start fueling, but will show normal lamdas, 14ish.

[CarJunkie]

Your log you posted may have that info already....can you post a screenshot that includes when you lifted off the accelerator and before ending the log?

[Nitro158]

Thanks here you go.

[CarJunkie]

I think that's proof of leaky injectors. If the hash marks at the bottom are time, you coasted in gear for 5 seconds and the injectors never stopped dumping fuel.

This is my most recent log, unfortunately a screenshot, so not as detailed, but I removed all data except accel pedal position, load request, load actual and the lamdas. Look how fast the lamda's shoot to max value when the injectors turn off....

[Nitro158]

Thanks for you input. Yeah its time along bottom. Wouldn't the AFR keep staying uo though?

Not sure if the factory fuel map haa little burble bulit in?

Originally Posted by CarJunkie

I think that's proof of leaky injectors. If the hash marks at the bottom are time, you coasted in gear for 5 seconds and the injectors never stopped dumping fuel.

This is my most recent log, unfortunately a screenshot, so not as detailed, but I removed all data except accel pedal position, load request, load actual and the lamdas. Look how fast the lamda's shoot to max value when the injectors turn off....

[CarJunkie]

No, fuel should cut off off on over-run (coasting in gear). Even a brief burble effect would only last a fraction of a second unless running a tune that lets you choose a liger duration.

Your log is exactly what mine showed when my injectors failed. I was also getting long cranks if the car was restarted when hot or warm but not cold, probably due to flooding, and frequent misfires.

I took it to dealer and the HPFP failed, so I had to pay to replace it. Once the new HPFP was installed, the injectors officially failed and got replaced under warranty. The injector warranty is extended to 10 years/100k miles. Unfortunately, the 1M was not included on the HPFP extended warranty that all other N54 cars got.

[PRTSB1M]

Originally Posted by CarJunkie

Unfortunately, the 1M was not included on the HPFP extended warranty that all other N54 cars got.

The design of the HPFP and the ease at which it can be replaced, makes me think BMW engineer's saw them as wear items that would fail farther out of warranty. It wouldn't surprise me if ethanol kills them faster than anticipated.

[schmick325]

I had a stumble at this rpm and it turned out injector number 6 wasn't reinstalled correctly after i'd had a new valve cover put on. The injector was sitting too high in the port and leaking combustion. I only realised when i put a set of index 12's in and the cyl 6 injector was a bitch to remove as the port was carboned up. Once all the index 12's were in and coded that stumble has been gone

[UberWagon]

I had this on my first 1M and it was the HPFP starting to go. I am not as familiar with MHD logging, but I believe you can log demand vs actual pressure for the HPFP (at least you could on Cobb). If the lines don't match up then you know the HPFP is due for replacement.