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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N55 Turbo Engine Tuning and Exhaust Modifications - 335i Tuning > N55 FBO PS2 odd engine 'stumble'



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      01-08-2020, 05:09 PM   #1
jlegelis
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N55 FBO PS2 odd engine 'stumble'

Gents - Car is an FBO E92 N55 XDrive 6MT w/ PS2, Stage 3 tune, 66k miles - recent build so still trying to debug. Under full throttle car feels like it occasionally stumbles or misses for a split second - feel it mostly through the seat. No codes, no lights, no misfires, and data logs look clean - car otherwise runs perfectly so not really sure where to begin.

Thoughts: Coils are original, plugs are 15k old and gapped to .022. Any usual suspects - really hate to start randomly guessing, but don't have a lot else to go on? Wisdom or good suggestions appreciated.

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      01-08-2020, 05:19 PM   #2
E92n55slo
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Your coils are at 66k? Replace those antiques. Also what do you mean by stage 3 tune?
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      01-08-2020, 06:00 PM   #3
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>> Your coils are at 66k? Replace those antiques.
Stock or aftermarket? What else while I'm in there?

>>Also what do you mean by stage 3 tune?
Custom tune by Wedge. I call it that because it's a bit more aggressive than the MHD Stage 2+ OTS maps.
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      01-08-2020, 06:06 PM   #4
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Your FBO PS2 on original coils and 15k plugs? I'd start there, you never tune on worn ignition components. And I hope you are running a proper custom tune, no clue what "stage 3" is.
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      01-08-2020, 08:09 PM   #5
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Quote:
Originally Posted by jlegelis View Post
>> Your coils are at 66k? Replace those antiques.
Stock or aftermarket? What else while I'm in there?

>>Also what do you mean by stage 3 tune?
Custom tune by Wedge. I call it that because it's a bit more aggressive than the MHD Stage 2+ OTS maps.
Your ps2 so you can run stock coils no problem or upgrade to precision raceworks coil kit if you want.
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      01-09-2020, 08:29 AM   #6
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Change your plugs to NGK-97506, they are a step colder I believe. It is what was recommended to me when I installed my PS2.

I believe the gap is .022 as well. I would connect with Wedge and have them review a log. It should be easy to see if it is a misfire due to ignition...

Every car is different, but I don't push pas 18 psi on pump 93. E30 I bump to 20-21 PSI. It is possible you are getting spark blowout depending on how much boost you are making. Or you could be crashing your HPFP causing it to stumble and misfire.

When you build a car like this you need to be aware of how it functions and know how to read a log. This way you are able to make your own diagnosis and don't take the chance of hurting the engine.
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      01-09-2020, 05:04 PM   #7
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Stumbles are usually ignition or fuel. I would start with replacing the coils. C2YT is right about the gap. Ideally you want to run the largest gap possible without running into blowout.
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