Hi RPM WOT misfire, only when cold out.

[JayRolla]

Ok for the longest time I was hitting a bad misfire above 6krpm at WOT. I thought it was fuel cut from a huge boost leak, but I still have the problem after a 2g maf and fixing most leaks. The SAFC only sees about 1800hz at 12psi so it cant be fuel cut.

Now if the temp is above 40* the car runs like a champ. When the temp drops it starts to do the missfire. Im running the 6es ngk plugs gapped at .028. New MSD wires, I swapped the coil for another one and it still does the same thing.

Why would the cold make it misfire more?? Should I try dropping gap to .026 or even lower to see if it helps? Thanks.

Also sometimes its a hesitation and sometimes its a huge misfire and if I do a quick downshift it will misfire even earlier around 5krpm.

 

[bmwisthekey]

Can you try using your stock maf again to see if that fixes the problem, also is it possible that your boost is spiking or creeping on you in very cold weather if it goes too high i suppose it could blow the spark out even if the plugs are gapped at .028, try gapping them lower to see if that fixes it, might as well its easy enough to do.

 

[romeen]

If it only does it when the engine is under a heavy load and the air is cold it could be that the a/f mixture is just too dense for the spark to bridge the gap. Gapping the plugs a little smaller could be diagnostic. But if it works then I would be concerned if that suggests a weakness somewhere in the spark "department". Just something to consider.

Do you have a wideband to see your ratios when it does this?

 

[JayRolla]

Yes it did it with the old maf. Its done it since I built the motor, even when it was stock, with only a 16g and exhaust. Im thinking maybe weak spark. What would cause that other than the coil. Ive swapped two coils.

 

[ChvyKc]

Yes it did it with the old maf. Its done it since I built the motor, even when it was stock, with only a 16g and exhaust. Im thinking maybe weak spark. What would cause that other than the coil. Ive swapped two coils.

You probably want to go with a colder plug. I always ran BPR7ES's in my car gapped at .28 after I started running more than 20 pounds of boost. I would get rid of the 6ES's and pick up some 7's. You can get them from NAPA for 1.30 a piece. It sounds like you are blowing the spark out causing something like fuel cut to happen. I assure you that you are not hitting fuel cut though (I know that AFC works correctly )

 

[romeen]

Have you checked your timing recently?

 

[ChvyKc]

Have you checked your timing recently?

I was thinking about that after I did my last post. Since it's just been doing it since the rebuild then you might not have the timing set just right. I would still go with a colder set of plugs either way.

 

[JayRolla]

SAFC works great dont worry about that. Im on a stock fuel pump so im running only 12psi. I shouldnt need the colder plugs at this low of boost. Also timing is at 5*BTDC.