Won't built boost past stock

[dsmcoder]

I have a 1991 auto gsx and my boost doesn't build past stock, when I floor it, it will go up to 13psi for about 1 second and then it goes to 10psi for the rest of the time at wot. It used to build to 14 before and stay there. When the turbo spools up I can hear a hissing sound, this just started happening. When it started making that noise I decided to do a boost leak test and I can hear a small leak, sounds like it's by the throttle body but I can't find it.

Anyone know if a small leak would cause this problem?

 

[Absit]

Yes.

How about you be a champ and tell us how you're controlling and measuring boost, too.

 

[Sik95TSI]

I have a 1991 auto gsx and my boost doesn't build past stock, when I floor it, it will go up to 13psi for about 1 second and then it goes to 10psi for the rest of the time at wot. It used to build to 14 before and stay there. When the turbo spools up I can hear a hissing sound, this just started happening. When it started making that noise I decided to do a boost leak test and I can hear a small leak, sounds like it's by the throttle body but I can't find it.

Anyone know if a small leak would cause this problem?

Yup fix the leak and it should be fine! A small leak can cause the turbo not to build full boost or hold boost! - Ryann

 

[dsmcoder]

Yes.

How about you be a champ and tell us how you're controlling and measuring boost, too.

I am using a mbc with an autometer boost/vac gauge and a data logger.

 

[Absit]

Then assuming your turbo/wastegate aren't borked, and you installed it all correctly, it's the boost leak most likely.

 

[Turpin1066]

Water.
Soap.
Spray bottle.

That should help find that leak.
Good Luck.

 

[dsmcoder]

I fixed the boost leak, now I can't find any. But the problem is still here and I can still hear the noise. The screw off of my mbc unscrewed all the way and spring fell out, I put it back in but do you think this could have caused this problem?

 

[Bud92gsx]

Heres what the hissing sound sounds like to me..Your boost gauge is not installed correctly and when in boost your hearing the air that supposed to be going into the boost gauge..

If you know what a turbo spooling sounds like and it's not that..Then I'm going to assume the boost gauge need to be looked at..Or at least the line going to the gauge needs to be looked at..

 

[90gsxjuice]

On the mbc did u put in the little ball that goes in with the spring

 

[volcomsnow245]

On the mbc did u put in the little ball that goes in with the spring

yea if the spring fell out then most likely the ball bearing fell out too.

 

[dsmcoder]

I seen the ball was still at the bottom before I put the spring in there, unless there is two balls? When the problem first started happening I think it was before the mbc screw fell off and I could hear the turbo spooling but my boost gauge wasn't working all the time.

 

[90gsxjuice]

Just one it should be on the turbo side

 

[Bud92gsx]

If the boost gauge wasn't working all the time and you heard the hissing inside the cabin..I bet there is a hole in the line, or you need to cut the end off where the line goes into the gauge , and re attach the line..I'm almost betting that what it is..I heard the same hissing when I drove my car when I had the guage out..

 

[daddyo]

You said before that you heard the leak coming from the tb? Does it still sound like its coming from there? Did you do the emissions bypass? Have you checked all the caps on the tb if you did to make sure there is not a crack in one of them?

 

[Bud92gsx]

Post 7 he fixed the boost leak..

 

[Gs Dewd]

You need to another boost leak test and check the gauge this time and the tubing to it. You have a leak somewhere or the gauge, mbc is screwed up. Also screwing the knob out on the mbc is for less boost, in for more boost.

 

[Bud92gsx]

Mine is the opposite for setting boost..Out it for more and in for less..But ya I would retest and get inside the cabin to confirm that it's a leak at the gauge or line..

 

[daddyo]

I fixed the boost leak, now I can't find any. But the problem is still here and I can still hear the noise. The screw off of my mbc unscrewed all the way and spring fell out, I put it back in but do you think this could have caused this problem?

And he can still hear the noise is also what he said Bud92. Unless it is a type o

 

[dsmcoder]

I can only hear the noise when driving but not when doing the boost leak test.

 

[Bud92gsx]

Have you ever checked your boost gauge during a blt? If not I would try it and see if the gauge reads what the pressure is set to..And if it does or doesn't listen for the hissing..