Boost Issue...

[COEyeDoc]

Just hoping to get some opinions/suggestions...

I recently did the TD04/TMIC (wrx) mod to my 93 SS and am having some boost issues. When accelerating, the car quickly boosts up to ~10-12 PSI, but then quickly fades to about 6-7 psi where it maintains. I can do this repeatedly....accelerate and it boosts up and fades off. When there is more of a load, the boost is a bit more, peaking at about 13 and maintaining around 8.

Any ideas why I can't sustain boost levels? BTW this is with a MBC.

Thanks!

[wtdash]

Sounds like a leak somewhere - how much do you trust your MBC?

How long does it sit @ 10-12 or 13 psi? The ECU's fuel cut kicks in after 3 seconds once you hit about 13 psi.

[COEyeDoc]

Sounds like a leak somewhere - how much do you trust your MBC?

How long does it sit @ 10-12 or 13 psi? The ECU's fuel cut kicks in after 3 seconds once you hit about 13 psi.

It reaches 10-12 PSI for 1 second at the most and quickly fades away. Doesn't feel like a fuel cut....I have experienced that in my old talon in the past. I have wondered about a leak, but really cannot hear one...

I have heard of people having trouble with the knock sensor, but I'm not sure that that would manifest this way??

[wtdash]

When I had a bad knock sensor it really limited the engine's output across the board - there was no boost spike w/a fade-off....just consistently slow. It was a different car (in a good way) once I fixed it.

I would recommend checking/changing it, regardless. I had 4 EJ22's in my garage this summer, and 3 had cracked knock sensor (all were <'95).

Did you check codes? http://www.surrealmirage.com/subaru/engine.html

An easy (?) test is to go back to stock, assuming you still have the boost solenoid, etc.

You should get 8.7psi out of it and it'll help diagnose the issue.

[Legacy777]

Assuming you have your MBC setup properly, boost control is purely mechanical, so it's either the MBC or wastegate solenoid.

Check Both of those as well as all of your vacuum/boost lines associated with them.

[COEyeDoc]

Assuming you have your MBC setup properly, boost control is purely mechanical, so it's either the MBC or wastegate solenoid.

Check Both of those as well as all of your vacuum/boost lines associated with them.

It was something with the MBC. I replaced mine with a friend's and it is working fine. Thanks for the suggestions.

[Legacy777]

No problem.