boost bleeding off

[Turbo Brian]

went to the track yesterday and got a couple t/o's in before the rain came and ruined everything my boost was hitting 18# and falling from there as i went down the track. normally my boost is a steady 20#. i could hear a noise, kinda of a whirring/hissing-type noise? hard to describe. the noise started a couple weeks ago, but i never noticed the boost problem till i was at the track. me and some guys looked over everything and the only thing we noticed was my belt may have been slipping (was getting a glaze on it). today i put a new belt on and went for a spin. the boost comes up to 20# but falls then goes up when i shift and falls again. (and still makes the sound). i think i have a leak of some kind somewhere. i checked my boost hoses, and they are ok. looked over my other vac. lines and didnt notice anything. i/c hoses are good. thoughts?

btw, the only recent change to the car was powerplate. one of the plenum bolts got stripped so 4 are tight and one is as tight you can get a stripped bolt.

 

[peterkin]

i'm having the same problem, someone please give us some ideas. i hate to leach off of your post, but i logged on to post almost the same thing. my car spikes 20 psi then falls back to anywhere between 14-16 psi and stays there. don't get me wrong, it pulls good and i get 3 deg maybe but it just won't stay there.

 

[Kevin Turch]

I just stripped my plenum bolt this weekend, might want to get it fixed, you might be leaking air from that bolt.

 

[NC87GN]

A local had the same problem with 19# - 16# from 1st to 2nd. First check where you have the lines running from and to your boost gauge. We were running an adjustable knob to adjust boost inside the car. As a result running all that line from the turbo to the inside of the car (driver side) caused the gauge to vary. To solve it we ran a line 2 feet from the turbo to the adj. knob and the car was rock solid 19#. Also run some good rubber lines to the wastegate turbo and solenoid. Do not use cheap thin wall hose as it tends to balloon under pressure. HTH

Mike Banas
87GN

 

[azgn]

fix the stripped bolt....more than likely that is the culprit.....

 

[Turbo Brian]

i pulled the plenum and there was evidence of a leak on the drivers side. i helicoiled the stripped bolt hole and used some copper rtv on the gaskets. i just finished and want to let the rtv set up so tomorrow ill know if that was my prob.

 

[Turbo Brian]

the bolt hole has been helicoiled and all 5 bolts are tight now. BUT the car still loses boost and still makes that noise. it occured to me what the noise sounds like though so maybe this will help.... you know that growling noise the ac compressor makes when you're on the throttle w/ the ac on? thats almost the same kind of noise im hearing under high boost. it doesnt do it under low boost. my ac is obviously off when i mash the gas and bring up 20# so its not that (and the compressor on this car has never really growled like on my cutlass and 442 anyway). so im not sure whats wrong. could a bad turbo make a growling noise and lose boost? i hope not.... i think my next step is a mightvac and test my actuator.

 

[tazgn]

Could it be that the alky is turned up too high? I don't really know, but when my alky kicks on it does make a strange noise as well. But the boost stays up. Also, I don't know what kind of chip you have but I thought some chips had a boost spike kind of programmed into them to give that extra burst of acceleration before it settles out to a set value. But my first bet would be the alky is drowning the car with the pump speed to high. But guessing here....

Derrick

 

[Turbo Brian]

the car has been "dialed in" since late april. got a new chip, set the boost at 20# and had the alky set. car ran great. i took the car to the dyno the day after i got it setup and pulled the #'s in my sig. ran fine and held boost. its only the last few weeks that ive noticed the sound. and didnt notice the boost prob till i went to the track the other day. i dont go wot very often i usually hold back a little when im out on the street and i get to 55 pretty fast and just let off so the boost prob coulda started when the sound started too i just never noticed.

a powerplate is the only thing ive changed on the car in recent weeks (middle of june). that was how i stripped the bolt hole. and i cleaned some carbon build up out the completely clogged egr passage while the plenum was off. i guess i could remove the plate, but i really dont want to chance stripping any more bolt holes. ive had that plenum off 4 times now.