Not Boosting Properly

[jreese86]

I've been trying to figure out the problem with my 1994 GSX since I bought it in February. I've spent hours searching, hours wrenching, and I still can't figure it out.

The car idles great. starts up everytime with no problems. It doesn't sputter or act unsual at all, except that no matter what I do it feels like a damn NT. It will build about 7psi at 4k, working it's way up to about 11psi at redline. You can't "feel" the turbo kick in at all. The car is Damn near 100% stock. I had cracks on my 1g manifold, so I replaced it with a ported 2g manifold thinking that was my problem. Still slow. Then I had the turbo looked at, and it had some cracks, so I replaced it with an almost new ported 14b and also installed a 2g o2 housing. Still slow. Hunted down and fixed 2 HUGE boost leaks, and 2 decent sized leaks. Figured for sure that would fix it. But no, it made ABSOLUTELY NO DIFFERENCE. I did a compression test: 165, 146, 165, 165. I didn't try doing wet test on the low cyclinder. I unhooked the hose to the WGA, no difference, still maxed out at 11psi at redline. Then I unbolted the downpipe, to check for a clogged cat. Still slow with the downpipe off. I'm out of ideas. So, to summarize:

It's not a boost leak.
It's not a pre-turbo exhaust leak.
It's not an exhaust constriction.
It's not an unhealthy turbo/wga.
It's not a vaccuum line problem.
It's not an unhealthy engine.

What else would keep me from spooling?

 

[shawn3168]

this is like the exact problem i have but mine will not boost past zero im thinking intake manifold gasket but i havent taken mine apart yet have you checked there?

 

[jreese86]

I have one small remaining boost leak, but the car holds 15psi for about 30 seconds, so it wouldn't affect performance this much.

Have you done a boost leak test?

 

[K_Hill]

Have you tried using a different wastegate actuator?

 

[jreese86]

Yea, I replaced the WGA when I replaced the turbo.

 

[phreak965]

any more news from this? my car seems like the same thing but sometimes my idle is low..i can't find any boost leak and my mileage is pretty low (about 22mpg hway)

 

[stomp]

I'd do a little more checking into that low cyl. That might be a source to your problems?

 

[98eclipsekidd08]

mines the same way but at 12psi wont hold anymore no matter what, my friend holds 14 no problem same mods it is aggervating.

 

[srumel]

Do you have access to a logger? Any check engine lights? I'd suspect either a Mass Airflow Sensor problem or possibly base timing. Are you basing the psi from an aftermarket gauge?

 

[vandenberg33]

I had a similar problem once and it turned out to be a weak fuel pump. If you have a guage watch your fuel pressure when you rev it up and see if it fluctuates alot. My car just wouldn't build boost well and would even studder at high rpms.

 

[B-Man]

Are you using a MBC? cause that sounds about normal for the stock wastegate. 8psi I believe is the stock wastegate setting.

 

[jreese86]

Wow, didn't see this brought back from the dead. I've since sold the car, but the problem turned out to be the WGA. It wasn't closing the wastegate all the way. I had to shim it so it sat closed.

 

[phreak965]

hey jesse, sory for the noobness, but i think this is my problem...how do you shim it shut?