Rb25Det Overboosting - Creeping, Not Spiking

[Brent]

Hi guys. Just as the title says, I've got an RB25DET in my R32 and whatever I do, the boost will NOT stay steady.

The motor is 100% standard. Standard turbo, intercooler, dump pipe, blow of valve, everything.

I have tried a few configurations though and nothing makes any difference. Have tried an RB20 actuator, t piece boost controller, aftermarket dump pipe and just recently a brand new GReddy Profec B Spec 2.

So like I said, even with stock parts, the boost level to 4000rpm will stay steady at 4.5ish psi, then gradually climb to about 8.5psi by redline.

It does it in every gear, although I found if you launch hard in 1st then the boost stays down a bit for some reason.. Whereas if you're on the freeway in 3rd or 4th then it will climb more noticeably.

I have checked the wastegate flap and moves very freely and does not get stuck at all.

What the hell is the problem?!

[GH05T]

what ecu are you using? diferent ecus, tunes will affect boost differently for different gears

[Brent]

I've tried two different standard RB25 ECU's, both have the same affect.

The car is standard. Fully standard. It has to be something broken or not functioning correctly, but what?

[DVS JEZ]

Have u tried a different dump pipe yet dude? Make sure the wastegate glap is opening conpletely. If it doesnt u need to modify/replace the dump pipe

[GH05T]

simple boost leak? the actuator is just not opening properly by the sounds, something has bottlenecked

[Brent]

Yeah, Jez I put the stock dump on yesterday and it made no difference.. Wastegate opens fine with the standard and aftermarket dump.

[GankTank]

By the sounds of it theres no problem. you still have the low/high boost solinoid? 25s have this, round 5psi before 4000 8psi after,

[Savtraxx]

if you buy me lunch at tafe tommorow , the problem will mysteriously dissapear.

[Marcus89]

If the actuator isn't opening properly then he would be having massive boost spikes. Would be more a case of the actuator not holding closed properly but then like someone posted above if he is still running the stock boost control solenoid then it could just be normal

[Brent]

The solenoid is non existent and the actuator and wastegate are both working CORRECTLY. The actuator has also been swapped out for one which has been proved in another car to be working properly.

Today the car stalled on me while coming off higher revs and putting the clutch in. To me this indicates a leak of some sort. I am getting a smoke/leak test done this Saturday to see if that is the case. The turbo to exhaust manifold gasket is brand new and there are no leaks there. I'm thinking the leak may be coming from the actual manifold to head gasket...

[restless]

Looking forward to your result...

[DVS JEZ]

Smoke test came up sweet. Noticed the TPS was stuck on 0% according to ecu. Checked and found the signal wire has a short to ground. Ran a new signal wire now TPS works.

Ran it up on the dyno with boost controller turned off. Ran 5psi then creeped to 8psi up top 177kw

Tried playing with boost controller with no rise in boost.

So

Turned it onto high boost and held a flat 10psi 201kw.

Next run te same. 3rd run boost dropped back to gate pressure. Suspect his boost controller is faulty

[Brent]

And Jez has done it again. Car now runs perfectly!

I completely removed the Profec B and switched back to the RB20 wastegate and now the car holds 10psi all the way to limiter. Stoked

So it looks like for some reason the RB25 actuator would not hold the same pressure (although I had the same result with another RB25 actuator), the 'brand new' boost controller was faulty (will have a word with who I purchased this from), and the TPS wiring (I had the R32 RB20DET > RB25DET loom made up by someone reputable) were all significant factors as to why my car would run how it did.

Other things which improved with how the car drove were brand new AFM and OEM o2 sensor.

Was definitely a bitch to get this motor running how it should, but worth it in the end.

Thanks again Jez!

Edited September 16, 2012 by Brent