boosting problems

[caniborrow50cnts]

ive searched for hours on answers to my problems, the car related ones. To put it simply, it sounds like my gst has a boost leak. You can hop in my car and haul ass as long as you dont use more than about 90% throttle. Between about 90 and 100% open throttle, the car sputters, misfires, and backfires. It also accelerates slower because of this, but if i were to let off the gas a little, it runs fine. The CEL occasionally lights up with codes p301, p302, p303, p304, and most recently p1105. The 301-304 codes are cylinder misfires, but the p1105 was the fuel solenoid, which i check the wires and replaced with a working one off my gsx, but no fix. I could tell you everything i have already checked but it would take too long. So I can only hope all you nice fellows out there could come up with some ideas because my CEL doesnt want to.

[steviek]

Do you have stock intercooling piping? Cause I remember I had something like that happen to me everytime I hit 10pSi or so it would stutter hard. It was because I had blown a hole in the plastic UIC (located under the fuse box). And it would hold a certain amount of pressure then blow open wider than a dutch prostitute.
BUt your misfires and stuff seem like plug problems; are you running platinum plugs cause those are horrible under boost. that would result in the backfire/misfire your getting.

[caniborrow50cnts]

i have swapped the plugs out of my gsx, which are ngk, and no improvement. engine is about 80% stock. stock intercooler. k&n intake. greddy bov. i have leak tested this car about 40 times. Found leaks from one of the rubber hoses connecting the intake pipes, the adjusting screw on the back of the bov, the idle adjusting screw, and the injector seal on the 4th cylinder, and pcv valve. i readjusted the hose clamps to fix that leak, replaced the injector seals, and replaced all the vacuum lines. stole the little rubber plug, off my gsx, that is supposed to cover the idle screw. disconnected the vacuum line to the bov and pcv valve and plugged them and leak tested again and found nothing. still runs crappy.

[steviek]

It could be your front o2 sensor, its a long shot but if that shits the bed, the ecu goes into this extremely rich safety loop mode where peoples cars run incredibly shitty.
I'm sorry man you seem to be on the ball with checking/diagnosing problems and you've done everything that I would do.

[caniborrow50cnts]

interesting theory...i will have to see if the wideband o2 in my gsx will fit my gst. on a better note though, the ecu has registered p0304 three times today. so if it is specific to 1 cylinder, maybe it is a different issue now. besides, what are the odds that my car had 3 different leaks that started about the same time? time to do a compression check again. it came up 10 off before between the 2nd and 4th cylinders. it just doesnt seem like a cylinder issue since it runs good most of the time. if the comression check come up the same, im gonna swap the plug and injector for the 4th cylinder and see what the ecu picks up then. im about 2 days away from swapping every vacuum sensor on with the ones on my gsx. though it may sound retarded, i have yet to find the line to the boost gauge. maybe i should double check the vacuum line diagram.

[Black99GST]

you dont really have a boost gauge vac line if your talking about the stock one... it doesnt work like that IIRC its all calculated throgh a sencor b/c it is electric. dont quote me on that though...

[caniborrow50cnts]

Originally Posted by Black99GST

you dont really have a boost gauge vac line if your talking about the stock one... it doesnt work like that IIRC its all calculated throgh a sencor b/c it is electric. dont quote me on that though...

i couldnt find anything in my manual about it, but that would explain why it isnt instant like the second gauge in my gsx. im having a hard time finding a leak tester though.

[Black99GST]

check your LICP... i bet its right there, just past the metal elbow from the turbo... thats where mine was and that bastered took FOREVER to find!

[SLoe]

Originally Posted by Black99GST

it doesnt work like that IIRC its all calculated throgh a sencor b/c it is electric. dont quote me on that though...

True. The ecu calculates boost a boost leak should look like you are overboosting on the factory gauge and you will run rich, sputter, and run like shit.

[caniborrow50cnts]

well i have some good news. The 4th cylinder plug had became fried in the past 3 weeks. i overlooked the plugs since they have always worked and i found several leaks. ive heard bad things about bosch platinum but they worked good since i bought the car 16 months ago or about 17k miles ago. i also swapped them when i first noticed the problem with no improvement. i guess the constant misfire ate it up. i went all out and bought the oem ngk plugs, for 4.29 a piece. well worth the $20.