Boost Max Lowered, Then Detonation, High MAF V and High IDC's
 

Cross Posting. Any ideas?

http://forums.nasioc.com/forums/show...5#post39874605

Check your bypass valve. I bet it is leaking. That will not show up on a boost-leak test, because it is looping back into the inlet, which is also pressurized during the test.

I *think* we successfully tested for that. We pressurized the TMIC (with Y pipe and bypass valve attached). We then plugged the end of the Y pipe that connects to the turbo with a plug and connected the small nipple on the bypass valve to the plug (so it would see boost pressure). Then we were able to fill that system with 22PSI before it started leaking through the BPV.

I tried to borrow a bpv locally, to make sure, but no luck on I-Club.

I think it's the MBC. When we did the standard boost leak test through the inlet, it started leaking and making a funny noise at 8psi.

no clues...

you could apply my tried and true (expensive and stupid) methodology of if no one can figure out your problem, beat on the car until the problem gets that someone can figure it out... :)

Could also be the turbo going out, and/or a boost leak in the turbo only when it's hot (unlikely though)

Those Hallman MBC have a bleeder hole that typically "leaks" during a boost leak test.

Hmm. Cory just put a low milage stock boost turbo in about 20K miles ago. It should have tons of life left.

I took it to EQ Tuning and they did a boost leak test and didn't find one but they said my MBC was cranked up really high. I said, whatever, the boost gauge and logs show that it's set to 12 PSI.

So Ed put it on the dyno and didn't find any problem when he adjusted the boost and logged it. He said it still runs stronger and smoother than 95% of the other bugeyes out there, which I think was a backhanded compliment. :P He tweaked the tune a touch, but he said it was perfectly fine.

So it's still a mystery, but it's fine for now. Ed's theory is that the boost leak test somehow fixed a boost leak that was there, but my friend and I did the same boost leak test a couple days earlier and again a couple days before that. I'm just crossing my fingers that it doesn't come back.

The car feels like a beast! He says the power is the same as last time he tuned it (even though I've added PnP'd stock headers and a Perrin silicone turbo inlet). I'm waiting for the dyno graph to see if there's more area under the curve though. I know my injectors are maxed out above 6K RPMs but he said it should be safe in all but the coldest of weather (denser air).

wow so your car has healed it self.. ... mine never do :( maybe i should check the hole in my race cars block to see if its slowly closing up? lol

It was pretty weird. Seems fine now except now I have a "dyno tune" instead of a "road tune".

:omg: