[joaozinho_7]

Hi guys,

I've serviced my 2011 335i N55 DCT PWG today and found carbon build up on all 6 spark plugs. Initially, I thought it could be an AFR issue, running too rich perhaps, but ruled it out due to some logs recorded during WOT. 14.39 @ 2500 rpm tapered to 12.55 @ 6000 rpm. What else could it be? The car is MHD stage 2+ tuned 98 RON.

[anjuna]

It’s direct inject gasoline. Take a look into the general carbon buildup issues that surround that technology.

Have you ever had the vehicle walnut blasted?

Buildup is “normal” on the N55, but not this much. And you are correct about AFR - that’s not terribly rich. Still, I’d rather see black than grey/white.

[joaozinho_7]

Originally Posted by anjuna

It’s direct inject gasoline. Take a look into the general carbon buildup issues that surround that technology.

Have you ever had the vehicle walnut blasted?

Buildup is “normal” on the N55, but not this much. And you are correct about AFR - that’s not terribly rich. Still, I’d rather see black than grey/white.

Originally Posted by anjuna

It's direct inject gasoline. Take a look into the general carbon buildup issues that surround that technology.

Have you ever had the vehicle walnut blasted?

Buildup is "normal" on the N55, but not this much. And you are correct about AFR - that's not terribly rich. Still, I'd rather see black than grey/white.

I walnut blasted it last summer. I might be inclined to cold spark plugs, as I went from stock ones gapped at 0.031" to NGK 95770 gapped at 0.022". I changed to NGK as I started to get misfires. Yet, I live in Scotland and it's not hot throughout the year, 25 Celsius max in the summer for about 5 days lol... I do a lot of city driving too, which doesn't help the plugs either...

[anjuna]

Originally Posted by joaozinho_7

I walnut blasted it last summer. I might be inclined to cold spark plugs, as I went from stock ones gapped at 0.031" to NGK 95770 gapped at 0.022". I changed to NGK as I started to get misfires. Yet, I live in Scotland and it's not hot throughout the year, 25 Celsius max in the summer for about 5 days lol... I do a lot of city driving too, which doesn't help the plugs either...

Yeah, the "short trips" combined with GDI make for a hard time.

The colder plugs gapped smaller do not help IMO, though your mileage may vary.

I have stuck to stock BMW plugs (yes, the STOCK plugs) at the stock gap and had very little issue.

Was the walnut blast performed before or after you had these plugs put in?? If the blast was after these plugs were installed, there's a good chance that these just got all mucky before the blast happened, especially if the build up was quite extreme.

My only other pointer could be that you possibly were burning oil, though that tends to present itself in different ways, but the "short trips" could cause this sort of behavior.

IMO - stick to stock plugs, be glad these aren't grey/white. Call it a day.

[joaozinho_7]

Originally Posted by anjuna

Yeah, the "short trips" combined with GDI make for a hard time.

The colder plugs gapped smaller do not help IMO, though your mileage may vary.

I have stuck to stock BMW plugs (yes, the STOCK plugs) at the stock gap and had very little issue.

Was the walnut blast performed before or after you had these plugs put in?? If the blast was after these plugs were installed, there's a good chance that these just got all mucky before the blast happened, especially if the build up was quite extreme.

My only other pointer could be that you possibly were burning oil, though that tends to present itself in different ways, but the "short trips" could cause this sort of behavior.

IMO - stick to stock plugs, be glad these aren't grey/white. Call it a day.

Originally Posted by anjuna

Yeah, the "short trips" combined with GDI make for a hard time.

The colder plugs gapped smaller do not help IMO, though your mileage may vary.

I have stuck to stock BMW plugs (yes, the STOCK plugs) at the stock gap and had very little issue.

Was the walnut blast performed before or after you had these plugs put in?? If the blast was after these plugs were installed, there's a good chance that these just got all mucky before the blast happened, especially if the build up was quite extreme.

My only other pointer could be that you possibly were burning oil, though that tends to present itself in different ways, but the "short trips" could cause this sort of behavior.

IMO - stick to stock plugs, be glad these aren't grey/white. Call it a day.

Got the those plugs after the walnut blast. I've been researching and it might be due to them being too cold or running rich during part throttle. The coolant sensor might be one of the culprits too. I'm gonna take some standstill and part throttle logs to see whether it's running rich.

[lurker14]

I would blame that on plugs to cold, there is no reason to use anything but stock plugs/gap on stock turbo unless you are having issues.
carbon issues from direct injection only happen on the intake valves because they do not get washed with fuel. If anything direct injection would be less likely to to build carbon on the spark plugs because the fueling is more precise.

[TunafishE93]

The plugs are the stock temp not the one step cooler NGK 97506 so i dont think that is the issue. You are on the right track, you took a log at WOT but you probably dont drive that way normally. I would suspect you are running rich during normal driving.

Do you do burps? I would think that this might also cause carbon build up but that is speculation..

[Mdilo]

Did you ever find out what was causing the carbon build up on your plugs? I'm having the same issue but only on #6