Ok, well before i tell you what the problem is i'll give you a little background on the car. well i bought my 1990 s5 TII a little over 2 months ago, when i bought it she had a badly slipping clutch in her. I got the car home , put a new ACT clutch in. and the first thing i noticed was that my boost bleeds down from whatever it was at to 4 PSI. I think the guy who had it before me knew because he kept trying to find an s5 turbo manifold, thinking that was the problem. when i bought it all it had done to it was HKS intake filter, HKS catback exhaust. and an HKS turbo timer. Since ive had it ive done quite a few things, my sig shows what ive done.

so heres my problem, As of right now i have my MBC set at 11 PSI, when i floor it it will rocket up to 11psi until about 6000 RPM after that it will slowly, but uniformly fall to 4 PSI until redline. It almost looks and feels like my turbo is too small and if being outflowed. But i would really doubt that because its only 3 more psi then stock.

Well i first thought it was a bad turbo or manifold. i switched those for a new ones, nothing happend, same problem. I only have 2 vaccum lines in my car an i dont think those are leaking. But why am i only bleeding boost when i got into the higher rpm's????? Ive checked for restrictions in my intake system, air filter, afm and TID. but nothing was wrong. my exhaust shouldnt be a restriction either, because i have a straight pipe all the way back. I think it might be a boost leak somewhere so i switched out all the pipes from the turbo to the TB elbow with nothing solved. Could i have a leak in my innercooler somewhere?


come on guys, someones got to know. Just start giving me things to check, and ill eliminate things one by one.
thanks

Jerry

 

I'm a bit confused - you mention HKS cat-back, but your sig says custom single to a Dynomax muffler?

If it is a Dynomax Muffler, which model?


-Ted

 

Yea i took off the HKS catback, I didnt like the sound and it had cats on it. So now i have 2.5" straight pipe back to the dynomax. Im not sure what model it is. its a straight through design with holes punched in the side.

You have any idea of what could be causing my problem ted?

jerry

 

i think it could be a flow restriction some where anyone else have ideas

 

come on guys, SOMEBODY here out of the 20 gazillion people has to have an idea.

 

Turbo is bad.
You've got a intake vacuum leak.
Is the hose under the BAC valve clamped on both sides???


-Ted

 

My turbo is bad? Thats kinda wierd that i would get two turbos that have the EXACT same problem. I was thinking i had a leak somewhere. but i was thinking more of a boost leak then a vaccum leak, because my car still pulls excellent vaccum.
Yea my bac hoses are all clamped good. i too off my upper and lower intake manifolds and replaced all the gaskets and vaccum lines. didint help anything. i also switched my IC pipes with a buddy, that also didint do anything. could it be a leaky IC?

Jerry

 

Vacuum (at idle) might be enough to such the hose closed.&nbsp Does the vacuum change on a cold versus warmed engine?


-Ted

 

hah, I just notice the hose from my intake to my bac doesn't have and hose clamps and after a hard run I notice it almost blew off and there was a small vac leak, I was woundering what the flamage and hesitation I was getting at 6k and at 9psi....

 

hmmm. Ok well if the vaccum coul dbe enough to suck it closed then which hoses should i check? all vaccume lines and such? even my boost guage line? And no idle doesnt change from warm to cold temps. It stays at 18-19 IN of vaccum all the time at idle.

Blackrx7- what was your problem? did you have the same boost problem im having or what? im not quite understanding what you said.

Thanks guys

Jerry

 

you might be running to rich or something as well... that'll hurt boost. the 2.5" exhuast might be hurting too.

 

if im running rich that would cause a boost problem? How would the 2.5 inch exhaust be hurting it? if anything i would think it would help it, unless ure saying i need to go bigger. But my friend who has an s4 has the exact same exhaust system as me doesnt have this problem. and also i had this problem before i had this new exhaust.

Jerry

 

ideas guys? come on i need some ideas.

 

problems still there

 

Is there a chance you guage is bad?

 

Have you tried watching how the boost level reacts with the MBC out of the system? I'd try removing the MBC and see if you get a consistent boost level.

When troubleshooting things like this, always simplify it as much as possible. If the pattern stays the same, then it's something in the turbo - either worn out or something is funky with the wastegate.

Speaking of...have you ported the wastegate?

At first glance, it sounds like a boost leak, but usually boost leaks will come on sooner and at lower pressures from all I've seen.

 

this is jerrys friend. we have have taken the b/c off and just connected the wastegate. it runs 5.5 psi until close to 7krpm then it bleeds off to 4. when it startes to bleed off of 5.5psi its the same rpm when the b/c is connected when it drops past 5.5. there are almost no vacuum lines on the car.

 

yea, i get the same problem, no matter what boost level i run at.

 

did your car do this before you went "bare block"?

 

yep, it had the same problem when i bought it. But i couldnt tell because it had a badly slipping clutch. the guy i bought it from "claimed" he didint know it was happening, but i searched through his former posts and he was looking for a new manifold thinking it was leaking boost. he didnt know much about 7's

-jerry

 

Ive seen that a lot of people have this problem. I actually found this thread through a search because I also have the same problem.

Ive come to the conclusion its just the turbo. I could be wrong...But it seems odd that so many people would have vacuum/boost leaks that cause the exact same problem at the exact same RPM.

My boost doesnt bleed all the way to 4...But it definately starts dropping after 6000RPM.




Anyone have some more input?

 

Ok, I've read this thread many times before and I have the same problem.
My car: 90 TII
dp, hi-flo cat, apexi N1 duals, apexi intake, apexi BOV, 720cc secondaries,3 degrees advance timing, s-afc, dyno tuned for 11.0 A/F ratios to redline, greddy profec B set for 11psi stable.

Ok, We've checked for vac leaks, none appearant, steady idle, TID crack free and in real good shape, turbo has zero play and spins great. Car pulls great.

My problem is this, at about 3300-3500 rpms I have 11psi of boost which is great but at 5800-6000rpms my boost all of a sudden bleeds down to 6psi. I mean as soon as I approach 6000rpms the boost just falls down to 6psi by 6300. What is causing this? I'm sorry but I don't understand how it's the turbo when I've seen people put down more horespower than myself with the stock turbo. I have 220 rwhp now. I don't think the turbo is holding it back. Help Please!!!
-Seth

 

Like I just said, Im fairly confident that anyone with the stock turbo has this problem. I hear everyone has it. I have it also. Ive also heard that these cars cant hold boost to redline even in STOCK form.

Dont worry about it too much. Its just the woes of a horribly mismatched ( turbine/compressor ) turbo.

 

So my only way to solve this problem is to get a quick'n'easy hybrid turbo?

BTW: I also do have a slight exhaust leak at the manifold. That shouldnt cause it to only happen at 6k rpms though right?