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Old 05-13-2023, 10:05 AM   #1
mccohens
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Member#: 429303
Join Date: Sep 2015
Default Overboost on new stock motor FIXED

My stock 05 baja turbo was rebuilt 2000 miles ago, all stock. In addition the wiring harness was replaced, injectors cleaned and balanced to 90%. Any rubber hose that was crusty went out too. Oh, new coil packs and plugs, good stuff not amazon crap. I cannot get past about half throttle without getting overboost at about 4000 RPM. Have a scangage so I can see some stuff. Boost is over 15, probably around 17 when the fuel cut happens. Wastegate moves properly at 8 psi pressure in the garage, also tested the overboost valve and it holds pressure without voltage then releases properly when energized. There is one pill I can feel on the turbo side of the "T", according to some sources that is correct but I also find info that there are 2 pills with different diameters and placement is critical.
I did disconnect the overboost valve and boost maxes around 5 and it will rev higher without any issues. But I would sort of like to see what it runs like with stock boost limit working.
Tried the search function but no useful info. Hope this post gives me some ideas.

Well the boost valve was working but someone reversed the hoses! I first tested it in the car, but then removed it to see if the lines were OK. They were fine but on backwards. So now it runs great and I can give it more than half throttle.
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Last edited by mccohens; 05-30-2023 at 08:51 AM.
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Old 05-13-2023, 11:11 AM   #2
PhoSho
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Member#: 515595
Join Date: Jun 2020
Chapter/Region: MAIC
Location: Northern Virginia
Vehicle:
2004 Forester XT 5MT
Cayenne Red

Default

Well, if you are overboosting will a fully stock setup, it can really be only one of three things: 1) Wastegate not opening correctly or fully stuck, 2) Boost solenoid not operating correctly, or 3) Vacuum line routing/restrictor pill placement is incorrect.

It seems like you have checked the first two items reasonably well, so I would check #3 to make sure things didn't get mixed up during the reinstall. Your vacuum line routing and pill placement should match the image below. Also check the line with the pill and verify that the pill is not plugged.

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Old 05-13-2023, 11:55 AM   #3
19std
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Default

Or there's the nasioc standard:

4. There's a whole bunch of stuff i left out, but it's stock.
5. It has a tune on it for a Ferrari 458, because cobb ots looked similar.
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Old 05-13-2023, 12:34 PM   #4
PhoSho
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Join Date: Jun 2020
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Location: Northern Virginia
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2004 Forester XT 5MT
Cayenne Red

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Quote:
Originally Posted by 19std View Post
Or there's the nasioc standard:

4. There's a whole bunch of stuff i left out, but it's stock.
5. It has a tune on it for a Ferrari 458, because cobb ots looked similar.
Lol - or that ^
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Old 05-13-2023, 12:57 PM   #5
mccohens
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Default

well if it has a tune it was not on my watch. The pill is in the correct side, I doubt it is clogged as with the valve line unhooked boost caps at about 5. Works great then but a little boring.
I am wondering if a clogged cat could cause this. Lost part of a piston ring in the previous motor and never found a trace of it. Also blew a ton of oil thru the motor when it went bad. Is there a way to check cat function? I have a temp gun, would think a clogged cat would run a lot hotter.
The only "mod" is I have the egr heads and non egr pistons so the compression ratio is a tad higher. Now I know of several options but had no idea when the motor was built. The plan is to get a tune with max boost limited to about 12. It is a truck not a hot rod.
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