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HELP Not making full boost

1

1slowhatch

New member
Just bought a stock 97 gtp. It doesn't feel as quick as it should. Has loud rattle at idle (at blower). 140,000 miles. The little boost gauge only maxes out at 1 line past halfway. Are these cars supposed to fill the whole gauge stock? If so, does that mean my blower is worn out?

IF so, i plan on buying a lower mileage m90 and porting/pulleying it. Then swapping in the new one in an afternoon. I can't just pull it and check out the rotors/bearings because the car can't sit down that long.

THANKS
 


Check the vac lines around the boost bypass valve and the plug on the solenoid. something may be unplugged or broken. I think the computer limits you to 4psi if something is wrong with the bypass. That would be something close to a little over half way up the digital gauge.

And, as far as the rattling: That's probably the sc coupler being worn out. They usually do that after the 100k mark.
 
cool. i'll check out the vacuum lines. is there a diagnosis procedure for the bypass valve?

what are the chances that there is something wrong with the blower... ie chips in the rotors or lack of coating...would that lead to less boost?

thanks for the fast reply!
 
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if the rotors were chipped they would eat themselves and end up in the engine. that isnt the case.
 
what about loss of teflon coating?


i take it you guys are confident it is just a valve problem and coupler. i'll order a snout rebuild kit and go from there.
 


the teflon coating would just make you lose boost. it would still run, but you wouldnt be able to hit the peak boost it once had before.
 
If the previous owner had the bypass valve off for any reason and didn't put it back at the correct position, you wount show full boost either. Just something else to look at will your under the hood.
 
update:

i replaced all the vacuum lines easily accessible

heres the weird part, i can spray starting fluid on the boost bypass valve (black cylinder) and the idle will definately change. does this indicate a leak at the cylinder itself?

i'm also getting ready to install a boost gauge. where should i tap into for a reliable reading?
 
oh yeah, i also messed with the location of the bbv. i've tried all the way up, all the way down and somewhere in the middle. doesn't make a lick of difference on the boost gauge.
 


Sounds like the bbv is bad. Basicly it is sealed with a boot type fitting that seals around the rod. If you can spray it on there and it does change the idle then i would look into changing that out.
 
put an actual boost gauge on it. it peaks 4 psi or so.

here's the weird thing, i tried disconnecting the vacuum line to the bbv, forcing the little arm on the supercharger all the way down. then, in park i revved it up to 5k or soo, and it was peaking out the digital boost gauge. i assume with the arm down it should be like running the blower with no boost bypass setup.

however, after taking it for a drive, setup without the upper vacuum line hooked up to the bbv, and it was making the exact same boost.

so i guess, it can't be any part of the bbv. how about the boost solenoid ( right next to it) it could be when i spray it, it was getting into the hole on the electric solenoid. also, should there be an open nipple on it? (no hose hooked up)?

if not, i don't know whats going on..
 


Ok I go outside right now and take the vacume line off of my bbv right now and go drive it it will do the same thing.by taking the vacume line off you are doing the same thing. It's not goinh to make full boost even if you're bbv was good if you take the vacume line off.



If you hook all the vacume lines up like they are suppose to go and can spray underneath the bbv and the engine rpm changes then you have a vacume leak at the rubber boot that the rod rides on.


I have an extra one that I just got. If you pay shipping then i'll give it to ya for free.
 
Yep [email protected]


I'm going to ship off some stuff in a little while so let me ship it off first then i'll let ya know how much to send.That way i don't overcharge you on the shipping.


Just send me you're address and i'll go ahead and ship it out in a little while and then let ya know how much ya owe me.
 
Sent it off yesterday, shipping was 9 bucks sent it through usps.
 
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