Thread: not getting full boost?

first post here want to say hi everyone first.

i have a 98 grand prix gtp, had it for about 5 months now trying to learn more each day. now i have a problem with the car not making full boost. on the stock digital boost gauge it only goes up to half way. it always went up full boost before, i have heard that if there is a leak in teh vacuum system the stock computer will limit the psi and the guage only goes half way. i just got done talking to a gm mechanic and he had no i dea what was going on said it was fine. but its not, i have a leak in the top 1/4 of my gas tank i have yet to get fixed would this mess up the vacuum system and cause this? or is there something else you know of? plz help me been trying to figure this out for alittle while now. also would a pre tuned computer from zzp fix this? also is there any way that the heat now has something to do with this?

Originally Posted by Standby

first post here want to say hi everyone first.

i have a 98 grand prix gtp, had it for about 5 months now trying to learn more each day. now i have a problem with the car not making full boost. on the stock digital boost gauge it only goes up to half way. it always went up full boost before, i have heard that if there is a leak in teh vacuum system the stock computer will limit the psi and the guage only goes half way. i just got done talking to a gm mechanic and he had no i dea what was going on said it was fine. but its not, i have a leak in the top 1/4 of my gas tank i have yet to get fixed would this mess up the vacuum system and cause this? or is there something else you know of? plz help me been trying to figure this out for alittle while now. also would a pre tuned computer from zzp fix this? also is there any way that the heat now has something to do with this?

Sounds like a vacuum leak. Leaking fuel tank should be fixed as its too expensive to have it spill out but would not affect boost. ZZP pcm wont fix your problem. Lots of good info and threads on how to check for vacuum leaks. Read lots.

thank you, and the leaking tank only leaks above 3/4 tank just keep it under that thank you

Originally Posted by bluegtp91

check the "T" fittings around the blower.

the first T fitting on the very front is kind of lose i can pull it up then push it back down. anything?

just remove the line going to the bbv solenoid, plug it you wont have any more problems.

you guys keep saying plug the solenoid, now if i take that line of and plug the solenoid and just leave it will it do and damage? and how do you want me to plug it, if that hose has a leak in it it will still leak wether i plug it or not right? and the T under the snout is solid its the other one that i can pull the lines out like nothing

the problem with the bbv solenoid they used from the factory is that its normally open. so to close it during normal operation, it has to be constantly energized, so when it fails it is in the open position, letting boost go to the lower side of the bbv actuator diaphragm, opening it and restricting boost level.

you idea worked i plugged the hose with a screw got my full boost back, now what exactly is teh problem? the solenoid needs to be replaced or the vacuum hoses?

thanks alot man really helped

i would just leave it off, it really serves no purpose other than warranty claims.

that solenoid doesnt control the boost bypass valve under normal operation though

Originally Posted by gtpinsc

the fuel leak is probably from the O ring on the fuel pump.You can access the fuel pump through the trunk.peel back the carpet where the console folds in back seat and there is an access panel to get to it.This happened to me before.

thanks ill look into that, been trying to avoid 300 bucks for a new tank haha