[J90]

Hi there,

I bought a 2008 335i with about 85k on it now. When I installed my first tune, the car misfired badly under WOT and I got the following codes:

P29CD = CYLINDER 1 MISFIRE
P29D0 = CYLINDER 4 MISFIRE

Since I have an extended warranty, i took it into the dealer. They said none of the injectors, coils or plugs are bad (all were changed out under prior CPO/maintenance plan), but say that the buildup in the combustion chamber is bad and want to do that process. My warranty doesn't cover it.

Is it possible that the misfires are caused solely by the carbon build up?

Please respond ASAP with opinions...I need to get back to the shop today.

Thanks!

[Ingeniator]

Originally Posted by peakay

Hi there,

I bought a 2008 335i with about 85k on it now. When I installed my first tune, the car misfired badly under WOT and I got the following codes:

P29CD = CYLINDER 1 MISFIRE
P29D0 = CYLINDER 4 MISFIRE

Since I have an extended warranty, i took it into the dealer. They said none of the injectors, coils or plugs are bad (all were changed out under prior CPO/maintenance plan), but say that the buildup in the combustion chamber is bad and want to do that process. My warranty doesn't cover it.

Is it possible that the misfires are caused solely by the carbon build up?

Please respond ASAP with opinions...I need to get back to the shop today.

Thanks!

Yes it can cause it. When where the plugs changed try switching coils around to see if the misfire moves. Does the car stumble at idle when warm?

[Jklad]

Yes it can, but usually the issue is a plug or coil pack. Try switching around coil packs and/or plugs as the previous poster suggested if you know how to. If valve cleaning has never been done on your car, you'll want to get it done regardless. Don't pay more than $500 for this job though.

[J90]

Originally Posted by Ingeniator

Yes it can cause it. When where the plugs changed try switching coils around to see if the misfire moves. Does the car stumble at idle when warm?

It doesn't stumble at idle when warm. I notice stumbles at idle about 50% of the time I drive it on cold start.

The plugs have just under 30k on them.

[Jklad]

30k could be a plug.

[J90]

Originally Posted by Jklad

Yes it can, but usually the issue is a plug or coil pack. Try switching around coil packs and/or plugs as the previous poster suggested if you know how to. If valve cleaning has never been done on your car, you'll want to get it done regardless. Don't pay more than $500 for this job though.

The dealer says in diagnostics they can find no codes or anything thrown related to the coils or injectors. They have all been changed in the past, so I can't necessarily doubt them on this. The SA did say they were getting some codes on the valves not working properly due to carbon build up - is that possible?

[J90]

Originally Posted by Jklad

30k could be a plug.

Even though its been gently run in stock conditions by the previous owner? Spec is 45k to change them.

[Ingeniator]

Originally Posted by peakay

The dealer says in diagnostics they can find no codes or anything thrown related to the coils or injectors. They have all been changed in the past, so I can't necessarily doubt them on this. The SA did say they were getting some codes on the valves not working properly due to carbon build up - is that possible?

You could get vanos codes. But I think they are messing with you. The service procedure for misfire is change plugs coils injectors then valve cleaning. You have another dealer near by?

[Jklad]

Or, have them commit to helping you out in some way if the valve cleaning does not solve the problem. You should prob still get it done regardless, though, depending on cost. At 85k valves would be pretty gunky.

[Tiago@VRSF]

Carbon buildup will certainly cause a mis-fire if it's bad enough but it's generally easier to diagnose it by replacing the plugs (inexpensive) and then shuffling the coil packs to see if the mis-fire follows the bad packs.

[pwr hungry]

Carboned up intake ports generally causes rough idling and dips in rpm at idle. I would start with plugs. If you're at 30k and added a tune, you're gonna need plugs soon anyway. Just take the advice given in this thread. None of us have anything to gain or lose based on what you do, whereas the stealership does.

[blbrchnk]

Without starting another topic, I am having an issue similar to this only in my case I don't get any misfire codes. In my case when the engine is cold and I start it, it rev's up and slowly backs down stably and then every once in a while (maybe every 3-5 minutes) it will shutter hard, revs dip and it sounds almost like it is starting back up. When this happens the turn signals dash as if either the car was just started or the engine hit 160*. Could this be plugs or coils? Like I said no codes whatsoever but it is certainly odd behavior. Nothing out of the ordinary once the car warms up, runs like a charm.

[djkevinnn]

They told me the same thing. Quoted $750 to walnut blast....

[Ingeniator]

Originally Posted by blbrchnk

Without starting another topic, I am having an issue similar to this only in my case I don't get any misfire codes. In my case when the engine is cold and I start it, it rev's up and slowly backs down stably and then every once in a while (maybe every 3-5 minutes) it will shutter hard, revs dip and it sounds almost like it is starting back up. When this happens the turn signals dash as if either the car was just started or the engine hit 160*. Could this be plugs or coils? Like I said no codes whatsoever but it is certainly odd behavior. Nothing out of the ordinary once the car warms up, runs like a charm.

If you have your JB4 cable log L_fp and H_fp during the cold start. I had some bad stumble when the temp was below -35. Almost dieseled and the idle was so low I would get voltage issues in the cluster lights. It was caused by my fuel system being so cold my HPFP was having problems.

[J90]

Originally Posted by blbrchnk

Without starting another topic, I am having an issue similar to this only in my case I don't get any misfire codes. In my case when the engine is cold and I start it, it rev's up and slowly backs down stably and then every once in a while (maybe every 3-5 minutes) it will shutter hard, revs dip and it sounds almost like it is starting back up. When this happens the turn signals dash as if either the car was just started or the engine hit 160*. Could this be plugs or coils? Like I said no codes whatsoever but it is certainly odd behavior. Nothing out of the ordinary once the car warms up, runs like a charm.

Please post elsewhere...thanks!

[blbrchnk]

Will do, although this is happening in my garage as well which should be around 50-60* regardless of what it is outside. I'll try to log it next time and see if fuel pressure is dipping.

[spxxx]

I was having the same issue around 90k. Misfires in multiple cylinders, I replaced plugs and coils and the Misfires were still there.

Finally got walnut blasted and it runs like a dream under WOT - still no Misfires on jb4 map 5 and 30% E85. Unfortunately the stumbling on cold idle is still there, I feel like this will never go away.

[J90]

I went ahead and approved the walnut cleaning as the dealer agreed to a price that was very near the lowest price I've seen it done on here. Since they were also replacing the valve cover gasket under my extended warranty, they agreed to replace the plugs for only the cost of the parts. Im happy with the deal and hopefully will be with the outcome as well.

Thanks for all the help. Will post a follow up on here after driving it and trying the tune again if anyone is interested.

[chili36]

Take it to another dealer.

Also if you need walnut blasting done hit me up for contact info of the guy who did mine. $250

[techwhiz]

From someone that went through this.
1. Plugs first.
I had a miss only when the Cobb was installed. These engines are very sensitive to plug issues at anything over the factory boost.

Plugs solved my issue. If running a tune, 25K miles on plugs, 30K max.

2. Carbon build up is not covered by warranty/CPO but a poor leakdown test will get them to do walnut blasting/intake valve cleaning.

My car failed a leakdown test after I complained of rough idle.
Carbon is more likely to cause rough running and not throw any codes for a misfire.

They found oil on the seals and that required a full head dis-assembly and rebuild.
I guess that took care of the dirty intake I complained about, that they wouldn't do anything about....

[007_e350]

I've done walnut blasting myself and I can tell you it cant cause misfires - with forced induction its almost impossible - pls dont waste ur time and money, WB can only improve rough idle and that little screw in our brains

[Jklad]

Originally Posted by 007_e350

I've done walnut blasting myself and I can tell you it cant cause misfires - with forced induction its almost impossible - pls dont waste ur time and money, WB can only improve rough idle and that little screw in our brains

My good friend who's a mini tech says that mini valves often gunk up real bad causing misfires pretty frequently.