BMW running, misfire issues, black spark plugs HELP!

[Teaspoonlizard]

Looking for some help with my 116i F21.

I have had the car remapped now for maybe 3 years and have had multiple issues with misfiring. First time it happened, coil pack seemed to resolve the issue. The next, ECU repair. The next I send the ecu back for repair again, no issue so coil pack + spark plugs fixed it. The next, just a spark plug.

It's been about a year since the last problem and it's come back again, I tried replacing all plugs which hasn't resolved it. Now misfiring under load on cylinder 1. Swapped out coil on cyl 1 with a used spare, improvement but still misfiring under load.

Something that I noted when changing the spark plugs is they were ALL fouled. Looked like Carbon fouling to me. The car was remapped at Superchips and I've asked them for their opinion on if the fuel mixture for the map is too rich but they assured me it's a closed loop system so that can't be the case.

A while back I thought it may be a leaky injector on cylinder three, but now all the spark plugs are black. Even the new ones after about 5 miles! I thought maybe an O2 sensor but no fault codes and I checked the AFR, at idle the commanded and measured was at 14.1 which doesn’t seem to unreasonable?

i also noticed what seemed to be some oil on cyl 4 spark plug, on the outside, but haven’t had any problems with misfiring on that cylinder... wasn’t mentioned before when I took it to a family friend mechanic and I trust him. Moved house though so no longer easy to take it to him...

I’m pretty sure the issue with the plugs and coils is because of the carbon build up, destroying plugs and in turn destroying the coils...

Looking for some guidance here as I've run out of ideas. Can anyone offer some advice? Anyone have similar issues?

Thank you.

 

[TCJBOLDIE]

Hi and welcome

Wile I have no experience with your make the basics are the same with all petrol powered engines IMO.

I can't see how an over rich mixture the usual reason why the plugs turn black can possibly "destroy coils"

I would remove all the injectors and have them sonicly cleaned and flow tested then take the car and have it put thru the paces on a dyno by a highly experienced tuner to check the fuel flow,fuel pressure regulator,ignition as well as injector duty cycle to find out if they are part of the problem.

IF the faults can't be located and eliminated and you absolutely love and want to keep the car then I would look at installing an aftermarket computer that is easily tuned/mapped to run the engine only and the factory EMS all the rest.

 

[Teaspoonlizard]

Hi and welcome

Wile I have no experience with your make the basics are the same with all petrol powered engines IMO.

I can't see how an over rich mixture the usual reason why the plugs turn black can possibly "destroy coils"

I would remove all the injectors and have them sonicly cleaned and flow tested then take the car and have it put thru the paces on a dyno by a highly experienced tuner to check the fuel flow,fuel pressure regulator,ignition as well as injector duty cycle to find out if they are part of the problem.

IF the faults can't be located and eliminated and you absolutely love and want to keep the car then I would look at installing an aftermarket computer that is easily tuned/mapped to run the engine only and the factory EMS all the rest.

Thanks for the suggestion, my understanding is the plugs foul and require more power to spark so they draw more current through the coils and cause carbon traces within the COP which then creates a path of less resistance so it arcs making the problem worse and worse. Only happens under load at first then at all times as it deteriorates. I may be wrong but that’s how I understand it. Replacing coils and spark plugs seems to fix it temporarily but then it comes back... so the carbon build up seems to be the issue.

I have ordered a new coil for cyl 1 to see if that eliminates the problem for now and some BG 44k fuel additive to try and clean the carbon deposits... even a little. I will get it media cleaned when the Covid 19 situation dies down... thinking maybe change plug/coil type?

 

[thexav]

There could be an air restriction somewhere, are you running a panel filter or induction kit?

Is the turbo providing enough air and getting enough exhaust? (I'm guessing it's the N13 engine)

Any engine should self trim to avoid running rich but yours doesn't seem to be. I too would assume the maf or lambda sensor are playing up if the air is getting into the engine.

If you're not careful the catalyst will also be shot, they really hate rich fuel mixtures.

Replacing a coil pack just gave a stronger spark, the older one may have been slightly weaker so although it fixed the problem in reality I think it just gave you more headroom to play with.

 

[Teaspoonlizard]

K&N panel filter but only as of yesterday... thought it may help and it considering an induction kit. As far as I know the air flow and exhaust is okay. I have a custom exhaust on it with a wider pipe, cat back. CAT is 100% shot so considering decat. (It is an N13).
I agree re the coil & spark plugs they’re a temporary fix. I wander if I just need a carbon clean, walnut shell media blast? Maybe it’s a build up over years.... not sure.
I’ve been logging a load of sensors which I’d like to get someone to view. Any ideas who I can ask to take a look?

 

[TCJBOLDIE]

You need to be careful when re-oiling the K&N as it can affect the AFM.

Is your motor a direct injection type? as they can cause carbon build up in the inlet ports and valve backs which can be cleaned by media blasting.

If it is port injected then regular use of a quality cleaner will prevent any carbon build up in the ports and back of the valves FWIW I use a measured dose every fill.

Over here decatting has a hefty fine so would recommend that you install a higher flowing sports cat.