hey guys, got a problem i can't figure out. my car used to boost 16-17 PSI (PEAK) with a 2.9 and Stage 2 Tune. i had the car tuned for nitrous and the power or boost has never been there since, so i had the Stage 2 Tune flashed back in (NO NITROUS SINCE), well now i'm only boosting 12.5, it just stops when it hits that. any ideas what the problem might be? by the way my Intereceptor is showing 12.5, so it's not a faulty stock boost gauge. the supercharger does not scream as loud as it used to either. any ideas?

Thanks
Matt

 

I will throw some stuff out just to give ideas. belt slip, clogged cat, tune messed up?

 

clogged cat would cause more boost, and i don't think it's belt slip, because the boost is very consistent it doesn't jump around. the tune is a possibility though, but i wouldn't think it would be the tune being the GM Stage 2 tune

 

bump

 

I'm gonna have to say it's probably the boost bypass valve, or something to do with that. Might wanna check the blower, and make sure nothing happened to the rotors or anything, but first i would check the bypass, and make sure it closes and the way.

 

It's either the wrong tune or you have a malfunction w/ your bypass valve.

How does the car idle, cruise?

 

x2

 

the car idles and cruises fine, it's just not boosting like it should be. how exactly do i go about checking the bypass valve?
btw it IS the Stage 2 Tune because it doesn't redline until 7 grand

 

Couple of thoughts here, because they're basically what would cause this. I know they may easily be disqualified, but they have to be stated:

1) It is the S2 tune, but it's been altered by whomever tuned you. On an 06, you can reduce boost in first individually and 2nd on up as a group. No idea why anyone would do that to you, but max boost could be set to ~12.5psi easily.

2) Somehow you forgot that you put a stock sized pulley on.

3) Your boost bypass solenoid is malfunctioning, jammed, mis-aligned, etc. For it to be this consistent, it would have to still be functioning, just not functioning properly.

I'll see if I can find a diagram for you...

 

Boost controlling
belt stretch
boost bypass solenoid

Now it could be a tune related issue... I dunno but you can check the torque management section and see if they limited boost....

Now you really won't see full boost untill wideopen in 3rd gear!

 

it's not boosting as high in 3rd either. and the Stage 2 Tune was put back in AFTER the custom tune, so would that not erase anything that was done in a custom tune? i know nothing about tuning btw

 

When was the last time it ran correct?

After you answer that, tell us what was SPECIFICALLY changed and by whom...

 

prior to the custom tune. and it wasn't by anyone on here. and like i said idk anything about tuning so i don't really know what was changed, i just know he put a 'safe' tune in it for my nitrous

do i just need to try the boost bypass mod to check the the boost bypass solenoid?

 

maybe you hit the bypass and moved it somehow, try losening it and pushing it down as far as possible, and see if that helps.

 

ok i did the bypass mod and nothing, still 12.5 pounds. i put my old boost gauge back in and it reads the same thing, it sure feels like it's pulling more than 12 pounds lol. it did misfire pretty bad at around 4 grand it 2nd, idk where that came from, it's never done that

 

my 2006 is the same except stock and 11 psi.

 

hm... you have 2 boost gauges? is one manual, and one digital, or are both going off the pcm? it might be the map sensor.. but idk. maybe a vacuum leak...

 

i have the stock gauge, and my Interceptor

 

I've had a similar issue this past weekend. My boost was normally around 22.5 psi, but it was showing between 15 and 17 psi for some reason. I basically eliminated the boost solenoid from being a possibility by routing the hose that hooks up to the back of it straight to the bypass valve. When I did that, I got my boost back. So if you do the same and have the same result, then either your solenoid is bad, or something your tuner did didn't get carried over with his rewrite of your tune.

 

thanks for the help guys, i still haven't determined the problem yet though