nomead

Getting a weird boost surge that just seemingly started and hoping for some suggestions.

The car is a 2001 C5 2.7T with 324k miles.
Upgrades are K04s, gutted DPs, and 3" custom catback with mufflers + resonators.

My butt dyno feels like it pulls until 3k then flattens, they starts pulling around 4k again to redline, albeit with less authority.

Attached is a pic of two 2nd gear pulls logged this evening (forgive the false start at time unit 22, I thought I saw a cop on the side of the road). I also grabbed the lambda readings, and it seems like I am running rich. Voltage never climbs above .80 on any pull though the 4 readings plot over each other making it difficult to read. It looks like i am getting some overboost, which might mean the N75 needs to be tested replaced?

I also checked mass air flow which seems correct, peaking at 200g/s.

As for recent changes, 3 coils were shot so I replaced all 6, new sparkplugs gapped correctly, 3" exhaust was recently put in, both rear O2 sensors replaced.

The car is slowly coming together and any thoughts on what to isolate next would be greatly appreciated!

georgeb944

Use a boost leak checker to, well, check for boost leaks.

I'm guessing a small tear in one of the rubber boots, like the throttle body boot.

nomead

Ran a boost leak test, lobster claws and TBB are fine, but I do hear a leak between engine and firewall on driver's side. Feeling around by hand from both top and bottom still doesn't pin it a spot; I can only feel a slight breeze. The area seems to indicate it's related to one of the turbo connections but the subframe and swaybar are in the way. Will dig deeper another weekend.