surging (sputter) air sound?? leak or DV?? help

[one30five]

2011 N55 135i FBO

I installed a ER cp and AA FMIC a few days ago. I finally got out last night to make some pulls and had great throttle response and power

but....

when letting off throttle around 5th gear I hear a "psst psst psst psst" sound. The best way t describe it is it sounds like a BOV opening and closing quickly. Or, if you know anything about semi trucks, the unloader valve on a compressor.

I was thinking diverter valves going bad and its compressor surge. But the sound seems to be coming from the driver's side of the motor near the charge pipe. I can hammer on it and wind the RPMS up and let off and not get the sound if I only accelerate to say 50 or 60 mph.

I was thinking that the O-ring in the CP, where it meets the throttle body is bad and that maybe I have a leak there. I don't seem to be losing power though.

I've read that OEM CP has some diverter noise baffeling or something. Could this sound be normal and I just wasn't hearing it before, because of the baffeling? Any ideas for further testing? (logs seem fine, and not different from previous logs prior to install with the exception of lower IAT and little more boost)

[Dackelone]

I would double check your recent work, first.

[one30five]

yep. I'm going to remove FMIC and CP tonight and reinstall after inspecting all couplers and clamps.

That said, i can't think of many things that can go wrong on that install. other than leaks in the plumbing. Which, if a leak is occurring, i would think i'd have symptoms regardless of RPM, Speed, etc. Any time boost is being created i would think i'd hear something.

I'll follow up.

[Dmacc]

I experience something similar on my n54. When I have a vacuum leak I will hear the same thing, the wg isn't getting enough vacuum to pull it shut in my case.

[one30five]

Originally Posted by Dmacc

I experience something similar on my n54. When I have a vacuum leak I will hear the same thing, the wg isn't getting enough vacuum to pull it shut in my case.

sounds like a lead, based on how loud it is and the fact it sounds like a 2 stroke motor being choked down i'd say its probably more likely its the wastegate than the diverter valve. i think the DV would make more of a whistling noise or a "woosh"

I'll follow up with findings tonight

[one30five]

disregard my last comment. it made no effing sense. which makes me realize just how ignorant I am.

I understand that diverter valves recirculates air back into system

But how does wastegate work? when its open where does air go?

[edisapimp]

Originally Posted by one30five

disregard my last comment. it made no effing sense. which makes me realize just how ignorant I am.

I understand that diverter valves recirculates air back into system

But how does wastegate work? when its open where does air go?

The tailpipe.

[one30five]

So turns out nothing mechanical at all

Something cracked the plastic undertray and the driver side tray was hanging down.

80mph must have created the perfect amount of turbulence to smack it against the bottom of the car.

I removed the tray and went out to drive. bingo! that was it.

Then I spent all last weekend at the track. car ran great!!