kyle1853

ok so anywayss......as you might remember i had a post about a boost leak and found it inside the bypass valve.....well went to the dealer had them replace it ...figured it had to break in or something......dont think that anymore.....it hits a little more then before but still not right .....i was thinking possibly that vaccum line that goes from the top of the bypass valve to that solnoid looking thing that has a connector also on it....could that cause such an issue??? im looking for any solutions right now before i give up and trade my cobalt in

Backdrift

How much boost were you running before? What pulley are you running now? Still the Stage 2 pulley?

It very well still could be a vacuum leak as well.

Also, do you still have that tune on there from the last time, or did you change anything after the motor blew?

kyle1853

its all stage 2 except the pulley is 2.8

Backdrift

Probably the tune, bro'. Stage 2 tune was not mean't for a 2.8 pulley. Neither are the injectors for that matter.

A 2.8 pulley should be retuned and have 60#s, or else you could blow the motor again.
That's probably why your boost is the sucks0rz.

mrbelvedere

iTrader: (3)

if you unhook the line going from the intake manifold to the backside of boost control solenoid and plug it

Backdrift

This.

kyle1853

boost control solnoid is the one on the right of the valve cover with the connector also going into in on the right....and the line that goes like right in front of the fuel rail in the middle on the intake manifold.....? where do i plug it...and what is that suppose to do when i plug it? will it throw a light also?

ok i pulled it and pluged the line with a glow plug lol....but sadly it was still doing it....does that eliminate the boost control solnoid or could that still be it?....and any other ideas

mrbelvedere

iTrader: (3)

its the vaccum line that comes srom the intake manifold an dit runs to the boost bypass solenoid

Frew

iTrader: (9)

running a 2.8 without 60's/meth is dumb

Dirty25RS

Have you tried a different boost gauge yet?

I always check my instrumentation first before I start pointing the finger at other components.

Chevycobaltss3

iTrader: (2)

Corrcto Munro bro running a 2.8 and no 60s is dumb. With a 2.8 with heat your boost should be around 15-16 on average I make 16-17 with my ported blower and 2.6 another thing it could be is your bypass
cable diconect the hose going from the s/c to the bypasss and plug it and run the car so see if it is stil the same if it is then either your car has a clogged air filter. No back pressure , ported blower lol, or your tune.

Backdrift

He just replaced his bypass valve, I believe.

I'm sticking with the tune. He said everything is Stage2 but the pulley, and the Stage2 limits boost. As some one else said earlier in the thread, Stage2 Tune boost is limited to 12.5.

Also, running Stage2 anything is a smaller than 3 pulley is a disaster waiting to happen.

Chevycobaltss3

iTrader: (2)

Correct with the tune. But it 'll have full boost till he reaches 6500 which means he is prob getting the correct amount of boost. But depending on where he lives is his main issue I just tuned a car with a ported and polished blower that I did and he was running 15 lbs no leaks wut so ever I run 16-17 with my ported blower with a 2.6 so I don't think it's the tune. Could be belt slip a Vacume line leak. Could only happen under boost. Happened to me. On my 1jz Supra the brake booster hose had a a pin size hole that would only open under boost and I lost like 2 lbs of boost look for the obvios stuff also. Spark plug not all the way down, leaks make sure the bypass valve is fully closed at idle and at wot make sure iat2z don't get too hot

Dirty25RS

^That is really hard to read.

kyle1853

if i plug that then theoretically it would boost as much as it can with that pulley, correct?

Chevycobaltss3

iTrader: (2)

Best way to do it is dissconnect both hoses from bypass and sc and plug only the one from the sc to the bypass valve. And if ure bypass or solnoid is bad or if it's ure tune then you'll get full boost since there is nothing holding it back. Was is your max boost as of now?

kyle1853

no still the same...as of now ive done some talking with gm and some master mechanics....and it is making me lean towards i have a plugged cat....also some other things that have happended in the past i have done some harm to it and the way the car is acting has some simptoms..so i will take a look into this on saturday and run some test or put a scope in and i will let you all know..

Chevycobaltss3

iTrader: (2)

with a clogged cat the car would make more boost due to restriction in the exaust

how much boost are you running?

Staged07SS

iTrader: (25)

Funny, I always reached my peak boost of 15 psi at 7,000 rpm when I was GM Stage 2. It never limited boost back to 12.5 psi, and I never heard of such a thing. There are many versions/revisions of the GM Stage 2 tune though, so anything is possible.

Positive displacement supechargers do not bleed boost, so I don't understand how this can be.

Chevycobaltss3

iTrader: (2)

gmstage two actually does bleed boost so you dont over boost the motor at a high rev... but there are a lot of revisions to gm stage twos. so it could be possible you just got a revised tune.

Staged07SS

iTrader: (25)

My GM Stage 2 tune was an 07' revision. I'm going to have to look into this with Bill. 15 psi (GM Stage 2's avg boost gain) is far from "over boosting". Also, you don't have to worry about a high rev. That's what the set limiter is for in the tune.

Hell, my GM Stage 3 tune builds boost all the way until 7,250 rpm.

I'm not saying you're wrong, or this isnt possible. I just find it odd. I'll post my findings.

Chevycobaltss3

iTrader: (2)

yesah with a gm stage two tune, it is the same as a gm stage one tune and is the same a a stock tune, the only differences are pe enrichement timing and i think a little more, but a gm kit since it would be warrantied gm wanted to bleed off the boost so no one blew the motor, basicall keeping it safe. But a true gm stage two does bleed off.

oh yeah i mean gm just wanted to be safe so they wouldnt let the motor go into more boost then stock in the high rpms, another thing they changed for gm stage two was rev limit.

Staged07SS

iTrader: (25)

I know these things man

I see what you are getting at with GM wanting to be safe. Are you saying this bleeding of the boost is on the newer versions of the GM Stage 1/2 tune ?

By the way .... mine was a true GM Stage 2 tune, and the boost never bled off after 6,500 rpms.

I contacted Bill. He is one of the engineers that designed the GM Stage kits for the LSJ/LNF. I will post the information he gives me.

Chevycobaltss3

iTrader: (2)

Cool . No I understand you know about this. I really just want to know how much this guy is boosting because he could be fine he just think that he should be boosting more I dunno we will see.

Staged07SS

iTrader: (25)

This is my convo with Bill. See I knew GM Stage 2 builds boost until redline. I don't know who told you it bleeds the boost, but it is not correct.

Originally Posted by Staged07SS

Bill,

A kid on here claims GM Stage 2 bleeds boost at 6,500 rpm back to the stock boost level of 12.5 psi. I have never heard of such a thing, and never experienced it when I was GM Stage 2. My car would build boost all the way until the rev limiter. I know there are many versions / revisions of the GM Stage 2 tune, but I find this odd.

Is this true ?

Jeff, There are not any revisions or versions of stage 2 ( actually there are 2 a very early cal had an issue with idle stability with AC on and it was fixed) No changes have been made since then (2005). It has changed not since then and does NOT pull boost. As a matter of fact, boost increases right up to the redline and would keep adding boost if we let it go faster.

Bill

Also, I am with you on helping the OP figure out his boost problem