[Felixrobb]

Hi all,

I have a problem with my cylinder 4 and cant find whats causing it. I have misfires only in that cylinder and I already changed spark plugs, coils, injectors.
The misfires happen only when RPMs are below 3k (at idle and sometimes when i drive under 3k rpm). They happen when the car is warm, and its worst if the temperature outside is hot. Sometimes the car shuts off when im in traffic and i get like 40misfires in cyl 4.

Its been months and no one seem to figure out whats wrong! It's so frustrating. Any one have an idea what could it be?

The only code i get is:
118002 Mixture too rich

[thejeremyman9]

Did you compression test cyl 4?

[BMWILUVU]

Originally Posted by Felixrobb

Hi all,

I have a problem with my cylinder 4 and cant find whats causing it. I have misfires only in that cylinder and I already changed spark plugs, coils, injectors.
The misfires happen only when RPMs are below 3k (at idle and sometimes when i drive under 3k rpm). They happen when the car is warm, and its worst if the temperature outside is hot. Sometimes the car shuts off when im in traffic and i get like 40misfires in cyl 4.

Its been months and no one seem to figure out whats wrong! It's so frustrating. Any one have an idea what could it be?

The only code i get is:
118002 Mixture too rich

You might want to look at the intake valve, maybe starting to have carbon buildup. This problem as it gets worse usually causes lower RPM misfires.

[Felixrobb]

Originally Posted by BMWILUVU

You might want to look at the intake valve, maybe starting to have carbon buildup. This problem as it gets worse usually causes lower RPM misfires.

I had the intake valves cleaned last fall so i doubt this is the issue

[Felixrobb]

Originally Posted by thejeremyman9

Did you compression test cyl 4?

This was the next thing to do on my list, but the symptoms of a bad compression don't really match what I'm experiencing right?

[n55david]

Originally Posted by Felixrobb

I had the intake valves cleaned last fall so i doubt this is the issue

That was never gonna be the issue unless you had another huge issue with your pcv setup.

[n55david]

Originally Posted by Felixrobb

This was the next thing to do on my list, but the symptoms of a bad compression don't really match what I'm experiencing right?

I would check it. It can be a symptom yes. It just depends. Not likely but possible.

[Felixrobb]

Originally Posted by n55david

I would check it. It can be a symptom yes. It just depends. Not likely but possible.

Alright thanks, i'll keep you posted

[BMWILUVU]

Originally Posted by Felixrobb

This was the next thing to do on my list, but the symptoms of a bad compression don't really match what I'm experiencing right?

If your compression is too low you will not get combustion. Therefore the rich mixture detection by the O2 sensor. It may be a problem in development and therefore showing up at lower RPMS. The question if you are not holding compression in 4 relative to the others is why. Could be something wrong with cylinder 4, its rings, or even a valve. Where did you get your plugs/coils/injector done?

[thejeremyman9]

The tricky thing is, incomplete combustion will actually read as lean, not rich. The O2 sensor measures oxygen, not fuel, so any incomplete combustion (which causes both excess fuel and air in the exhaust) reads as lean. The O2 sensor doesnt care how much fuel is in the exhaust, since it doesnt actually measure the air/fuel ratio or fuel at all - just oxygen

Anyways, compression test cyl 4. If it shows as good (probably test all of them at the same time to get variance), then start swapping coil and plug with 4 and another cylinder. I know they are new, but new doesnt always mean good.

[Felixrobb]

Originally Posted by BMWILUVU

If your compression is too low you will not get combustion. Therefore the rich mixture detection by the O2 sensor. It may be a problem in development and therefore showing up at lower RPMS. The question if you are not holding compression in 4 relative to the others is why. Could be something wrong with cylinder 4, its rings, or even a valve. Where did you get your plugs/coils/injector done?

Oh i see! Thanks very helpfull
Everything is done at a BMW specialized shop so i'm confident everything has been done the right way, the parts are also all OEM.

[BMWILUVU]

Originally Posted by Felixrobb

Oh i see! Thanks very helpfull
Everything is done at a BMW specialized shop so i'm confident everything has been done the right way, the parts are also all OEM.

Unless you are comfortable doing it yourself, since obviously they had not resolved the issue on 4, I would take it back to the shop and tell them you are getting misfires they supposedly fixed and give them the Rich Mixture code. I'm sure they will know what to do just say they hadn't fixed the problem after spending $XXX and kinda mention a compression test maybe they'll do it for nothing.

[F32Fleet]

Wiring?

[Fondry]

i had the same issue, after chasing it for almost 3 months, an indy shop near me figured out it was the DME had a ground that was shorted out causing the misfire. I replaced my DME and it was back to perfect with no misfire

[Felixrobb]

Compression test done, compression is fine in all cylinders. So new spark plugs, new coils, new injevtors, compression is fine, no vaccum leaks..... ugh

[Felixrobb]

Originally Posted by Fondry

i had the same issue, after chasing it for almost 3 months, an indy shop near me figured out it was the DME had a ground that was shorted out causing the misfire. I replaced my DME and it was back to perfect with no misfire

I'll have a look at the DME. How much did the new DME cost?

[LA1Z24]

The valvetronic return spring coming off the intermediate lever will also cause a misfire. There will be a noticeable pop from the exhaust whenever that cylinder fires. Will almost certainly damage the cam lobe in the process. Had it happen to mine. Compression will show normal with this failure. Running compression test will show an abnormality in this cylinder compared to others. https://photos.app.goo.gl/Ms46TUtKVVp9wEuGA

[AlpineweissF10]

Was this ever resolved? My issue is very similar with cylinder 4 misfire and rich condition. New coils, plugs, injector, compression and leak down test all good.

[LA1Z24]

Originally Posted by AlpineweissF10

Was this ever resolved? My issue is very similar with cylinder 4 misfire and rich condition. New coils, plugs, injector, compression and leak down test all good.

Compression needs to be done while cranking, and also a running compression test. All of those CAN NOT test good, while having a misfire.

Remove the valve cover, and inspect the valvetrain.

[AlpineweissF10]

Originally Posted by LA1Z24

Compression needs to be done while cranking, and also a running compression test. All of those CAN NOT test good, while having a misfire.

Remove the valve cover, and inspect the valvetrain.

I did a static compression test by disconnecting the fuel pump and removing spark plugs and connecting compression tester and cranking for about 10 times for each cylinder. They all came in around ~210 (+/- 2).

I then did a leak down test and it showed less than 4% leakage for each cylinder.

Sounds like you did a running compression and that was the issue. I'll look into that next. Hope that's not the case.

[Felixrobb]

Originally Posted by AlpineweissF10

Was this ever resolved? My issue is very similar with cylinder 4 misfire and rich condition. New coils, plugs, injector, compression and leak down test all good.

Nope, Still not resolved...

[thejeremyman9]

Did you check valvetrain as mentioned above?