[Tyc0]

So I know there are a million threads on this issue but I have a little bit of a different question. Ever since I swapped a new engine into the car I have been getting stumbles and backfires on cold starts, particularly cylinders 4 and 6. I saved up and bought index 12's for bank two. Coded and installed two days ago and it still acts the same way. My question is would the spark plugs still be gunked up enough from all those days of leaky fuel to make the problem persist? If not does anyone have any other ideas? Plugs were replaced with engine and that was about 4k ago. New pre cat o2's, vanos solonoids, coil packs less than 10k old, all new vacuum lines, new valve cover gasket with engine swap, hand cleaned the valves with pick tools and some sea foam type stuff, not the best work but definitely good enough.

[Bimmer_Bro]

Originally Posted by Tyc0

So I know there are a million threads on this issue but I have a little bit of a different question. Ever since I swapped a new engine into the car I have been getting stumbles and backfires on cold starts, particularly cylinders 4 and 6. I saved up and bought index 12's for bank two. Coded and installed two days ago and it still acts the same way. My question is would the spark plugs still be gunked up enough from all those days of leaky fuel to make the problem persist? If not does anyone have any other ideas? Plugs were replaced with engine and that was about 4k ago. New pre cat o2's, vanos solonoids, coil packs less than 10k old, all new vacuum lines, new valve cover gasket with engine swap, hand cleaned the valves with pick tools and some sea foam type stuff, not the best work but definitely good enough.

Are you tuned? If so which map?
Were the spark plugs removed when you did the valve cleaning?
I would let the car sit overnight. Without starting it, take those couple plugs out and see if they are wet with fuel. Wouldn't be the first time I've seen people have problems with brand new injectors.
If they are not wet, you could try new plugs to rule them out. Stick with the Bosch ones so you don't have to worry about gapping, they seem to be the most reliable.

[Tyc0]

Originally Posted by Bimmer_Bro

Are you tuned? If so which map?
Were the spark plugs removed when you did the valve cleaning?
I would let the car sit overnight. Without starting it, take those couple plugs out and see if they are wet with fuel. Wouldn't be the first time I've seen people have problems with brand new injectors.
If they are not wet, you could try new plugs to rule them out. Stick with the Bosch ones so you don't have to worry about gapping, they seem to be the most reliable.

Tuned on custom 92 map by v8bait (Justin Hubenak), yes they were out when I did carbon cleaning. I will check plugs tomorrow morning and report back. Not sure I can use those bosch plugs with upgraded turbos? I've always used NGK

[Bimmer_Bro]

Originally Posted by Tyc0

Tuned on custom 92 map by v8bait (Justin Hubenak), yes they were out when I did carbon cleaning. I will check plugs tomorrow morning and report back. Not sure I can use those bosch plugs with upgraded turbos? I've always used NGK

Are you on a step colder NGk? What gap are you running?
I guess it would depend on your Tuner recommendations. I know the Bosch plugs have zero problems handling MHD stage2+ 93 map but I understand you are custom tuned.
Have you sent any logs to your tuner for advice ?

[Tyc0]

Originally Posted by Bimmer_Bro

Are you on a step colder NGk? What gap are you running?
I guess it would depend on your Tuner recommendations. I know the Bosch plugs have zero problems handling MHD stage2+ 93 map but I understand you are custom tuned.
Have you sent any logs to your tuner for advice ?

Yes one step colder ngk with .02 gap for 21psi. I actually haven't asked him about it I will reach out and send him a cold start log.

[Bimmer_Bro]

Originally Posted by Tyc0

Yes one step colder ngk with .02 gap for 21psi. I actually haven't asked him about it I will reach out and send him a cold start log.

Great idea. I know another user on here had a cold start issue with his MHD map. I think turning off the cold start warm up seemed to help.

[Tyc0]

Originally Posted by Bimmer_Bro

Great idea. I know another user on here had a cold start issue with his MHD map. I think turning off the cold start warm up seemed to help.

I'll give that a go as well, thanks !

[BSM n54iS]

Originally Posted by Tyc0

I'll give that a go as well, thanks !

Check your plugs out first for sure though just in case I say. I had cold start misfires start on me the day I put the 1 step colder plugs in at .022, FBO stock turbos ots mhd 2+. I regapped the 3 that were giving me constant misfires on cold starts, had the plugs like 3 inches from my face eyeballing them, and I had just replaced the older ones obviously, so I for sure didn't smell any fuel or anything on them, which is why I just turned cold start off and am chugging along now. I am a fan of no cold starts now, only for emissions and it purposely makes your car run rough just to warm up primary cats faster.

[Tyc0]

Originally Posted by Bimmer_Bro

Great idea. I know another user on here had a cold start issue with his MHD map. I think turning off the cold start warm up seemed to help.

Don't know why or how but I turned cold start off and it's the smoothest start I've had in a long time, I will still check plugs and send log to my tuner and report back. But thanks !

[Bimmer_Bro]

Originally Posted by Tyc0

Don't know why or how but I turned cold start off and it's the smoothest start I've had in a long time, I will still check plugs and send log to my tuner and report back. But thanks !

Awesome! Glad to hear. It just to warm the cats for emissions so it's a little pointless with dp's anyway. Thanks for the update!