When it started:
I just installed a Detroit Tuned RPM power stage 1 tune, one step colder plugs, and Delphi coils. Car ran beautifully the first day, most power I've ever felt from it.

Then the next day, I began to get very bad engine stumbling when at half to WOT on the road.

Symptoms:
- no CEL
- engine stumble under load
- exhaust sounds like a flap rapidly opening and closing. Like a rapid pressure difference noise coming from the back

What I've tried/inspected:
- replaced turbo inlet pipe after seeing a crack (reducer split but was in one piece)
- boost builds all the way to 20psi during stumble, boost seems fine (measured with torque)
- fuel rail pressure reported by torque peaks and stays somewhere around 2300-2600psi. I can update with exact number of needed
- cleaned MAF
- checked all spark plug gaps (Detroit Tuned actually had the wrong info, and I ended up putting them to .036in and then back to .022in/.6mm, did not help either way)
- intake temps are below 100 during pulls
- stumble is almost better at WOT, but acceleration is very slow, as if there was no boost
- I hear the blow off when letting off the throttle
- when slowly introducing load, boost gets to 3-6psi before stumble

I'm just stumped as to what this could be. I'll be bringing it to the shop soon to get it diagnosed there as well. If anyone even has an idea what this could be, I'd be incredibly thankful for it. I wish there was a CEL to narrow this down.

Other relevant info:
- car is 72k mi
- 2011, N18 motor
- I do oil ever 5k
- m7 noise maker delete pipe
- stock cat and sensors left enabled in tune
- car idles fine
- miltek MK2 resonated exhaust
- throttle position sensor reported in torque is correct
- chain tensioner replaced 2k mi ago
- chain was not measured
- when car is off, oil cap has some resistance when pulling it off
- no visible oil leaks, and oil level is fine
- no difference in sport mode
- HPFP has **not** been replaced to my knowledge
- walnut blasting has **not** happened to my knowledge

Thank you for taking the time to read through so much. I've been pulling my hair out trying to find similar problems but I've had no luck.

 

Sorry for resurrecting a two year old post, but did you ever find the answer for this issue? I’m having the same issue at 2 1/2k-3k rpm

 

Oh no worries, I should've came back here to post after it fixed. It ended up being a bad set of spark plugs from factory and the gap info that Detroit Tuned at the time (may still be the case) was wrong. I emailed them when I found it so hopefully it's fixed, but the NGK plugs at their factory gap worked. There weren't any obvious signs of defect from the ones shipped over from Detroit Tuned.

That said, another issue came up about 2/3 months later. I don't think they're correlated, but my low pressure fuel pump relay had a cold solder crack, which started by intermittently killing the car until it finally fully died. I solved that by re-soldering the cold solder snap on the ECU (passenger footwell relay ECU). Since then I have sold off the car as it just wasn't reliable enough for me.

Was a wicked fun car when it worked though...