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Registered
2002 Forester
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11 Posts
Discussion Starter #1
I installed a boost gauge today and after doing some driving and a few pulls my gauge only got up to 5 psi. I know normal should be around 11 to 12 psi. What is the reasoning it could be doing this? No cel or anything. Any advice would be greatly appreciated
 

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2019 Outback 3.6R ..... 98 Forester S - Atl, GA
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6,857 Posts
Where are you pulling the boost reading from? Also a restrictive hose can affect readings.
 

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04 Forester XT 4EAT
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64 Posts
Start with the easy stuff

check your boost control solenoid, might have gotten unplugged or something.

check for restrictor pill in line going from wategate to boost control solenoid, these sometimes get removed accidentally
 

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2012 XT Touring 4EAT
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3,748 Posts
More easy stuff.

Check your blow-off valve... they have been known to leak at high pressure (and occasionally at any pressure). A simple test might be to remove the BOV and fashion a blanking plate out of wood or plastic to fit under it. At least for testing purposes, you can drive without a BOV. Did your pressure improve?

Check the rubber duct between the intercooler and throttle body. Cracks, breaks, clamps tight, any obvious issues? For an '04, this straight duct is fairly simple and accessible. For the 09-13 XTs, Subaru fashioned an inaccessible 3-piece duct with removable ends - about 6 places to leak (compared to your 2). That's progress!

From the output side of the turbo to the mouth or input for the throttle body there should be no leaks.
 

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2004 Forester XT 4EAT
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1,271 Posts
Leaks are also likely on the turbo inlet (unless I missed that). That plastic pipe is 15+ years old and gone thru numerous heat cycles. There are good silicone replacements that do NOT require the IM to come off/be loosened - I did it.
 

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2005 Forester 2.5 XT
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1 Posts
Sorry to bump an oldish thread, but I had this exact issue. Vaccum was sitting ~9-8 at idle. Would only boost to 4PSI in 1,2,3. 4&5 would cap to 5PSI. Wastegate duty was completely capped on the AP at 90.2. AFR’s looked good, MAF Voltage looked good.

I’ve been trying to track it down for the past week.
I ended up replacing the IC and BPV with better condition stockers. checked and adjusted all the inlet, intake/couplers, IC, And TB hoses and clamps while I was there. Checked all vacuum lines and clamps, (ordered a silicone set because they’re all crusty on a 15 yr old car.) verified the restrictor pill size.
It ended up being the BCS. Verified with a buddies off of an 05 FXT. Now hitting 9-11PSI
Ordered for ~$110USD
Posting to hopefully save heartache for another owner with an old foz that might have been through a block or two
 

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2004 Forester XT 4EAT
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1,271 Posts
Just to clarify...for those that may find this:
BCS = Boost Control Solenoid, aka DUTY SOLENOID Valve, per Subaru.
BOV = Blow-off Valve, aka BPV = Bypass Valve (not identical functioning parts, but similar)

Google for better explanations than I can offer.
 
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