I got a GMPP clutch installed a little bit ago. I havn't been on it since I got it back because I was breaking in the clutch, but finally did a run and it does not seem to be boosting properly.

I put in an interceptor and it jumps to 12.5PSI when I hit it in second then builds to about 13-13.5 and at the top of third I was lucky to get 14. I replaced it back with my stock gauge and it was the same.

I'm on a 2.8" Pulley, stock header, stock exhaust, stock intake, nothing ported and it used to boost to 110KPA (16PSI) on warmer days (It's relatively chilly here).

I know boost is a measure of restriction and all that, but when my set-up has not changed and its not warm out why would it drop 2PSI. I tried the boost bypass thing with no luck. It seems to run fine, vacuum seems good and it seems to pull decent (I can't remember how hard it pulled. It's been a while). I cannot hear a boost leak either.

Anyways, any ideas? Or just don't worry about it? I have a spare SC in my room with a 2.8 on it so I'm going to throw that on or just the bypass valve from it onto my SC later this afternoon. But the bypass valve feels fine on the current one. Not sticky.

Joel

 

What is the boost gauge sitting at during idle? My guess is that you have a vac leak somewhere, you should be seeing more then that with a 2.8. What are your fuel trims like? Are you on a stock tune?

 

I have a canned ZZP tune (I know, get a tune. Happening this spring). I just put a spare bypass valve on my SC so I'm going to throw it back in, when I start it up I'll let you know the vacuum, but if I remember correctly it was right around -16 to -17. I do not know what my fuel trims look like, or my AFR, I don't have the kit for my interceptor yet or HPTuners.

Joel

 

The interceptor can read fuel trims and I am sure yours are way off. You need a tune badly but I doubt that is your issue.

Personally I really honestly suspect a vac leak. Usually cars sit closer to -20 vac at idle so you might want to pull the s/c and re-seat it to double check everything. Possibly might need a new s/c gasket, but it's tough to say. Either way, there is a leak somewhere.

 

Are there any vacuum lines on the tranny? I couldnt find any, but they would have taken them off to do the clutch.

Also I put in a spare bypass valve and reseated the SC. It now peaked out at 105ish KPA (Nearly 15.5PSI) and it is at -60KPA at idle (-17.5 in HG). All going off the stock boost gauge. I'll need to get my interceptor back in (will be doing so in about 15 minutes) to get more exact numbers. I've never really noticed, but should the boost climb with RPM's at all? It hits 90ish instantly then climed the last 3K RPM to about 105.

Joel