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not getting full boost?

S

Standby

New member
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?
 


Standby said:
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?
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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.
 
BBV solenoid problem, most likely. Take the line off the actuator (black can on the front of the blower) and plug the line, leaving the bottom nipple on the actuator open. See if you still have the problem.
 


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.
 
The procedure I outlined will tell you for sure if it's the solenoid. If it is, you can decide to fix the problem or to just cut the solenoid out all together. It's there so the computer can dump boost when it wants to, like during shifts or when traction control kicks in.
 


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?
 
The problem is either the solenoid itself or the electrical connection going to it. The solenoid is supposed to stay closed until computer tells it to open. When it's open, it's routing boost into the bottom of the actuator, forcing it up, which opens the bypass valve, dumping boost back into the intake of the blower. Yours isn't staying closed when it's supposed to.
 
I may be off on this minichopper but it was my understanding that by bypassing the blower you got better gas milage and the blower wasn't constantly producing boost thus reducing operating temperatures. I know this is an issue with the Whipple but I thought it was also true with roots blowers just not on the same scale.
 


Robotech said:
I may be off on this minichopper but it was my understanding that by bypassing the blower you got better gas milage and the blower wasn't constantly producing boost thus reducing operating temperatures. I know this is an issue with the Whipple but I thought it was also true with roots blowers just not on the same scale.
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You're right, but what he's suggesting doesn't affect the normal operation of the BBV. The solenoid is only there so the computer can dump boost, removing it just takes the computer out of the equation.
 
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.
 
gtpinsc said:
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.
Click to expand...

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