Choking under boost?

[boysatt]

I recently picked up a 2004 Grand Prix GTP, very nice clean car and got a nice deal on it. Loaded to the hilt, every option. Got one issue with it though. Under full boost it chokes, I can get it up to 7psi and it will jump between 4-7 psi at full throttle but does not feel like it has the power it should, almost feels like its choking. I have checked all vacuum lines and replaced all of them, all intake gaskets are new. Has a K&N intake on it and all is connected right there. Fuel pressure holds the same at full throttle as at idle, around 60 psi.

Also at full throttle it has a whining noise comming from under the hood, not what I am used to considering this is like my 10th L67 car, not the aftermarket intake making noise either.

Im stumped and Im a mechanic for a living. I have a OTC Genisys scanner and have had it hooked up to the car and checked every reading and nothing seems out of the ordinary, so im at a loss now.

[imdaman3]

converter clogged?? pull 02 sensor in exhaust mannifold and take it for a spin,

[blueguy]

If your a mechanic...and you don't know what is causing the whining noise under the hood of a SUPERCHARGED GTP...then maybe go back to school?

In all honesty...I'd check the BBV...could be that...or a bad coil or ICM...any CEL's?

[silverstreak]

A bad plug wire can cause this under load and be fine at idle and cruising speeds.

[imdaman3]

^^if he has a scanner and says everything checks out fine why would it be a wire or a coil ? wouldnt you think he'd notice a misfire, under misfire data on the OTC Genisys scanner?? (i have the same one) its goes into every detail on the car im sayin convertor

[boysatt]

If your a mechanic...and you don't know what is causing the whining noise under the hood of a SUPERCHARGED GTP...then maybe go back to school?

In all honesty...I'd check the BBV...could be that...or a bad coil or ICM...any CEL's?

Haha your funny. the whining isn't like I am used to on these engines, unless the series 3 is louder. All my series 2 cars didn't sound like this.

No CAT on the car, has a custom 3" down pipe without cat. Took it out again this morning since I'm more awake now and threw my scanner on it and took it out. For the first time ever it threw a code, p0300 misfire. Looking at misfire data I am losing cylinders 1 and 4 at WOT. Otherwise not a single miss. Swapped coils around, problem did not change. Brand New Delco plugs and wires. Going to pick up a ICM this afternoon and try that. Strange it only misses at WOT.

[imdaman3]

thats wat mine did and it was convertor but yours is probably the icm is goin bad