I have a jdm 4th series twin turbo. Pretty much stock engine except for intake rear section exhaust. I havent done much on it, still trying to fix the gas leak first. My mechanic said the leak is from the fpd, so i showed him the write up about the delete. Thats what im gonna do next along with injector seals.

My problem is, (trails done in 3/4 gear), before 4500rpm, i would reach 11psi. But as soon as it reaches 4500 rpm, it would go back to 7psi. Almost seems like lack of power when it gets closer to top end. Makes me wonder, have my turbo gone bad?
Or the vacuums on the turbo hooked up wrong?
Or like my mechanic said, the actuators are shot and i need new one (i sorta feel that its because he has a of rebuilt onse sitting in the backroom).
Or possibly due to the gas leak i have.

Should i hook up the greddy boost controller to try? Or what else?

Thx, and sry for the long story.

 

Is the stock downpipe still on the car?

 

it could also be the vacuum tank leaking, or the check valve on it

 

Yes, stock downpipe.

Where is the vacuum tank?

 

on the front of the engine

 

I had the same kind of problem youre describing, I read somewhere on here that the stock downpipe/precat can get plugged up and limit boost to 7-8 psi on secondary boost.

I bought an aftermarket downpipe off the classifieds here...problem solved

I'm not saying for sure that this is your problem, that's just what worked for me

 

Ok... im a lil confused! How many catalytic converters are there in our system?
I only see one in the mid pipe.

 

There is a pre-cat on the downpipe so 2, pre-cat & cat.

 

I see you're from Hong Kong, I don't think the JDM cars had pre cats...I'm not completely sure though

 

When I had that problem it was a cracked Y-pipe. When car had a boost leak and it would transition over it would default down to 7 or 8 psi on the secondary. It needed a certain amount of boost to switch over to the secondary.
I would start chasing down cracks in the plastics.

 

Ok, heres what i found today after i bepught it in to fixed the gas leak from fpd (did the banzai delete mod).
Also found a "vtc" or "vdc" solenoid broken.
And!!! Turbo exhaust gasket is leaking.

I can still smell gas fumes when im boosting, and after 4500rpm, the boost would slowly go down to 0 as the rpm approaches redline.