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Old 07-15-2014, 06:56 PM   #1
Jaredhaney
Scooby Newbie
 
Member#: 379293
Join Date: Jan 2014
Location: Northeast Georgia
Vehicle:
2005 Subaru Sti
Silver

Default 2005 Sti hesitates to boost past 8 psi SOLVED

I'm not entirely sure if this is the correct area, since the CEL isn't on and does not show codes or get better with an ecu reset, for this so I apologize in advance and will gladly move this to an area more suitable.

Some background info on the car:
The car was tuned at Topspeed in GA through a Cobb V3 Accessport in March. The only engine mods are an AEM short ram intake, catless down pipe and 3" exhaust along with the accessport. I replaced the spark plugs with OEM NGK plugs about 6,000 miles ago and all the intercooler couplers with Mishimoto couplers and heavy duty clamps. The car has 78,000 miles on it and up until now I haven't had a single problem out of it.

About a week ago I noticed that it didn't seem to be pulling as hard, but didn't think much because my a/c was on and it was 95 degrees outside. I turned the A/C off and did a few pulls on my way to work and my boost gauge would climb to the 8-10 psi area and just stop building boost until about 5000 rpm and then it would climb on up to about 14. In 5th and 6th gear wide open it used to build to about 18.5 psi and it will build to 16 psi max.

I called Topspeed today and they said to check for boost leaks as the most likely culprit so I pulled the intercooler and checked the y-pipe and checked the intercooler for oil and didn't find any in it or on the throttle body. I reinstalled it all and made sure the clamps were extra tight and nothing appeared to be leaking. While it was off I also pulled off the vacuum line with the restrictor pill and cleaned it since I've heard rumors it can cause that problem. Watching data on my accessport the DAM stays at 1.0 at all times, the knock sensors aren't detecting any sustained knock, just the occasional blip when highway cruising for long periods of time. The car is not using oil, isn't smoking on startup, and seems to be running and idling fine so I'm out of ideas that I can currently test without throwing parts at it. I can post logs if needed, I just have to download them off my cobb and figure out google docs if anyone thinks that they'll be of use.

Any ideas on things to try or to buy? I'm thinking of tossing a boost solenoid at it and possibly seeing if the recirculating valve isn't sealing shut or the wastegate is hanging open for some reason.


Edit:
Problem Solved
The electronic boost control solenoid was indeed bad and didn't throw a check engine light as being bad. I'm posting logs of what it was doing and what it is doing now in case anyone would like to see or in case it is somehow helpful to someone else.

Bad Solenoid:
https://docs.google.com/a/student.la...sJM/edit#gid=0

Good Solenoid:
https://docs.google.com/a/student.la...#gid=110038922

During the "good" pull my accessport somehow picked up second gear when the car was actually pulling all the way through 3rd and into 4th.
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Last edited by Jaredhaney; 10-11-2014 at 05:23 PM. Reason: Problem Solved
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Old 07-15-2014, 08:01 PM   #2
JonnyV2889
Scooby Specialist
 
Member#: 197384
Join Date: Dec 2008
Chapter/Region: NESIC
Location: MWV NH
Vehicle:
2006 WRX Ltd
OBP

Default

Either smoke test or build a boost leak tester. Visually inspecting isn't going to do a whole lot. Pull a learning view, not that it'll be accurate since you reset the ECU.
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Old 07-15-2014, 11:16 PM   #3
Jaredhaney
Scooby Newbie
 
Member#: 379293
Join Date: Jan 2014
Location: Northeast Georgia
Vehicle:
2005 Subaru Sti
Silver

Default

I reset the ECU about 4 days ago and I've probably driven the car for about 2-3 hours since then since I'm not showing any excessive knock on my logs. I'm gonna rig up a smoke test for it here in the next couple days when I get a chance.
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Old 10-11-2014, 04:49 PM   #4
Jaredhaney
Scooby Newbie
 
Member#: 379293
Join Date: Jan 2014
Location: Northeast Georgia
Vehicle:
2005 Subaru Sti
Silver

Default

Problem Solved! I made a smoke tester and found no leaks at all and then tested the boost control solenoid with a nine volt battery and it clicked like everyone online said it should. I decided to just throw some used parts at it since I didn't know anyone around to swap solenoids with so I just bought a used factory boost control solenoid on ebay and it solved the problem immediately. Happy my car finally makes quick boost again.
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