I have read just about every post on all the subie sites and not one person has come up with a definative answer. I have a MY03 WRX with a 3" catless turbo back and a gutted up pipe. Whenever I am at lower rpms and let the boost build by feeding it gas, it spikes to about .11MPA then back to .7MPA then up and down. It will continue to do this until after 5K rpm then taper off (with my foot mashed on the pedal the whole time.) My vacuum lines are perfect with restrictor in it, and I have no other upgrades than catless up & downpipe. Iv'e heard it might be ecu and to get cobb upgrade, but cobb tells me this isn't normal and wouldn't recommend an accessport until fixed. Should I replace/clean my wastegate, adjust the actuator arm or what? Come on.... there have to be guys out there that have figured this out, or can offer any new advice. Please help and bring on the feedback!!!

 

i dont know what to do, i think that its just dp. it probably doesnt have enought back pressure. i dunno??

i live near there. trying to get a meet near there.

 

i have an 03 wrx with just an up and down pipe and intake and my car does the same thing

 

Well,
yesterday I put on my stock downpipe and that leaves me with an up pipe and axle back. Still fluctuates, and spikes from .11-.7MPA. All hoses and vacuum lines are new and perfect with the brass restrictor. I cleaned the wastegate solenoid with some brake cleaner, reset my ecu and it's still the same. Lots of people are having these problems and I am determined to get it fixed and figure it out. I'm guessing now it's the ecu and I am taking it to get checked this week. I'll make sure to update...

 

just an FYI on the back pressure comment. Back pressure is made by the turbo so nothing to worry about there.
You could take the downpipe off completely and your car would be fine(usually better performance).

Most likely the problem you both are experiencing is the waste gate flutter common on the 02/03 models.

http://www.scoobymods.com/forums/sho...ight=wastegate

 

what are your RPM's doing? Are they increasing steadily or do they raise 250-500 and then pause, raise 250-500 and pause again until 5k? Thats what my car sued to do (the pulsing RPMs) but I don't know what the boost was doing sicne I had no boost guage. I brought the car to the dealership and they said it was the tranny computer "trying to protect the tranny" I guess from all the power the car had even when it was stock I laughed at them for suggesting Subaru put in a tranny (I have a 4EAT sadly) that couldnt handle the stock power and left. A while later I got an AP and Protune and the problem was gone (funny, the tuner didn't even touch the tranny computer )

 

The "tranny computer" is actually part of the ECU, there is just some sensors in and on the transmission that report stats back to the brain, like temperature.

I have a friend that had an automatic turbo baja with zero mods, he just drives a lot up and dowl hills and long distances. He had transmission problems related to transmission tempurature and the transmission would do all kinds of funky ****, like what you described.
He had his transmission replaced, clutch replaced, still a problem.
I think the subaru 4EAT transmissions are a problem on the turbo cars from the heat of the turbo being so close.

You thing you might want to try is using redline or royal purple in your transmission, something with low heat generating friction modifiers.

 

Backpressure = bad

mkay?

 

Sorry, was kind of tired when I posted.

Yes, back pressure is bad. Another reason not to stick big turbos on a 2.0L.

 

you dont put a big turbo on the car because there isnt enough gas to spin it

there is back pressure created by the turbo no mater what when you are on boost

the stock ecu is set to bleed off the boost as the RPMs go higher. even after you tune it for boost it doesnt hold. wheni put a vf 34 on with a helper spring it would hold 1.5 bar to redline

with teh stock turbo it would bleed off 6k-7k

the reason your boost level is going up and down is the ecu is trying to control the boost. its saying to the WG try this, thats too much try this thats too little try this
until it hits its boost target

 

1st you need to check the vac lines/fittings that run from the FBC (factory boost controller), WG (waste gate) and turbo outlet to make sure everything is hooked up correctly and snug (sounds like you already checked it). If everything looks OK you need to disconnect the FBC, run a piece of vac line from the turbo outlet directly to the WG. If boost holds steady at around 7.5 psi you know the WG is functioning properly and the problem is elsewhere. Next try to get someone to lend you their FBC for an hour and see if the problem persists.

When this happened to my 02 Cobb stage 2 WRX it was just a vac line that streched out a bit at the T so hopefully you luck out like I did.

BTW, the boost spike you are experiencing is not a good thing so if you can’t figure it out just run off WG pressure until you figure it out. If you keep running it like that you’re engine might go BOOM.

Good luck
Joe

 

im running 1.5 bar on a VF 34

it will hold 1.1 bar ona stock turbo

 

I'm not sure if you're post was meant to discredit my advice but if you bypass the FBC and you're running off wastegate pressure you should not be hitting 1.1 bar on a stock turbo. The WG should only hold around 7.5 psi.

I'm just telling him a way to find out if his WG is functioning the way it should.

 

BTW, to say that backpressure is bad (pre turbo) is dead wrong but too much back pressure would be correct. Post turbo backpressure = bad for performance.

mcdrama was correct when he said that the turbo creates backpressure.

 

Wrong wrong wrong wrong, backpressure is bad, in all applications, at all times.

This comes from people putting too large of an exhaust on an N/A car, which does eliminate backpressure, but it kills your exhaust velocity, which is why power is lost. The ideal system has the absolute lowest backpressure you can get while maintaining good velocity. Backpressure is bad!!!!!!!!!!!!

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