Thread: Low boost, block off boost bypass solenoid. Full boost returns..

Just as the title says, after TONS of reading I could not find the answer, even got a buddy on clupGP running a thread to find the answer and nothing yet.

Little back story- I have had my 98 GTP since November 2011. Since owning it, the boost has never risen above 3.4lbs. So I started throwing parts at it since I was unsure of what the culprit was. As of now it has

NEW
LIM Gaskets
Upper manifold gasket (between SC and LIM)
Throttle body gasket
Injector O rings(Lubed and wiggled in to seat them)
Vacuum Tree O-ring
MAF sensor
TPS
IAC
MAP sensor
Evap solenoid
BBV (from ZZP)
BCS (from dealership)
SC belt
SC Idler (old shredded to include belt hence new SC belt)
Acc. Belt
Cat conv.
U bend delete
Cat back (new pipe and mufflers)
Vacuum hose from TB to BBV to BCS to FPR to Snout to MAP to Tree to EVAP solenoid.


I have sprayed carb cleaner all around this engine to find NO vacuum leaks. I monitor my vacuum with the Torque app and it reads 20-21 at idle, yes I know a mechanical gauge is more reliable (not in budget right now).

So I ran across a thread where a wise person told the questioner to remove the vacuum hose between the BCS and FPR and run the hose JUST from the FPR to the snout and then unplug the BCS(electrical connection). READ post number 16 http://www.grandprixforums.net/booooost-68178.html

So I thought what the hell, why not. I did this and got full boost and so fun to drive now.

This has me wondering though

1. Why does this trick work?

2. What about that NEW BCS? (it's just sitting there now, not bolted to the BBV, the new BBV did not have the tab to bolt it down)

3. Are there any side affects of doing this?

Originally Posted by QUICKSILVER462

I found the vent plugged on the BBV solenoid on my car the day I drove it home after buying iy in 09'. It should have a little filter on the end of it, they get clogged with dirt over the miles and years. I removed the garbage and installed a 90 degree angle vacuum elbow on the end of it, cured the problem of not gatting full boost at WOT.

I figured that's what happened to my old BCS, so I bought a new BCS from the dealership. Thanks for the reply.

did u try unpluging the bbv solenoid the eletric part and see if it goes full boost then it might be the ecm is only letting it go to half boost

LOL nm just seen you did that i would say the ecm is causing it to not go full boost....i dont have it even hooked up on mine i just have the top of it hooked up so it still vents at idle

Originally Posted by 00grandprixgtp

LOL nm just seen you did that i would say the ecm is causing it to not go full boost....i dont have it even hooked up on mine i just have the top of it hooked up so it still vents at idle

Which brings me to my 3 questions and also can a bad ECM cause these types of symptoms?

Took pictures to show what I did.

Cap off the "T" were the vacuum hose from the BCS goes to


Unplug the BCS (electrical connection)


Let this end of vacuum hose from BCS just sit/ lay there


No tab for the BCS to bolt onto, came from ZZP that way


Full picture to include the messed up paint from carb cleaner landing on the snout, not happy about that, but had to do it for possible leaks.

1. you have no BBV, it's BCA or BCS.

2. you don't have to unplug the fpr to bcs, if you unplug the bcs wiring then you have no worries.

Originally Posted by BillBoost37

1. you have no BBV, it's BCA or BCS.

2. you don't have to unplug the fpr to bcs, if you unplug the bcs wiring then you have no worries.

Tracking and will correct the item description, thanks.

So does the ECM control the BCS?

Does a new ECM have to be programed/flashed for the specific vehicle or can I mount just any JY ECM?

Still wondering about the three questions I posted.

1. Why does this trick work?

2. What about that NEW BCS? (it's just sitting there now, not bolted to the BBV, the new BBV did not have the tab to bolt it down)

3. Are there any side affects of doing this?

Going to try something, the BCS has nothing to bolt onto. I'm going to make a metal bracket for it to bolt to and then hook it back up to see if that is why it does not work. Also replace fuse 21 to see if that is why it kept blowing. Maybe the BCS has to be grounded? It just eats me up that I have this part not working, even though after unhooking it I got full boost.

Update to this, I tried bolting down the Boost Control Solenoid, connected the eletricals and nothing. Still only produced 3.3 pounds of boost. So I opened the hood put it back to the disconnected option and back to full boost.

Some people might be thinking or wondering, "HEY" you got full boost, so why are you concerned about the BCS?

Well, I just don't like having a $40 part just sitting there doing nothing also I want to learn and understand the reason disconnecting the BCS worked.

Originally Posted by TexasTanker19kilo20

Some people might be thinking or wondering, "HEY" you got full boost, so why are you concerned about the BCS?

Sums up exactly what I thought after I read the first paragraph lol

Originally Posted by REDCOMPG

Sums up exactly what I thought after I read the first paragraph lol

I just want to know WHY, I don't like not knowing. Guess I just have to deal with it huh?

When in doubt blame Gold Racekar and call it a day


Or blame GM and that should stop any thoughts as to why lol.

Maybe I should put the BCS in for sale section

You should I'm sure someone's always looking for one. It'll find your pre gen search.

Only thing though, I modified the bracket on it. Oh well I'll leave it there and let people ask me why I have it unplugged LOL.

Put it in the garage..weight reduction.

Originally Posted by REDCOMPG

Put it in the garage..weight reduction.

LOL, I'm 336 miles away from my garage.