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2002 US market Subaru WRX with mods from the PO slowly lost boost over the course of a few weeks.

I noticed the boost gauge not climbing as high as it usually does under normal conditions. After a few weeks of symptoms it feels like its lost all boost, but is still derivable and only occasionally produces a 'System Rich' code. I've had the car for about 3 years and its been running consistently until the power loss.

Observations:

I can hear the turbo spinning
C clip is in place on the WG regulator arm
Starts, idles and runs fine outside of low power and very slow acceleration
OBD2mx via OBDLINK says peak boost PSI is about 1 at near-full throttle

Mods:

Huge intercooler
Bigger turbo
3'' straightpipe with cat delete
Came with an accessport, never used myself but leads me to believe its running a custom map

How can I isolate the failure? I'm inclined to believe it could be a vac leak, bad gasket, stuck WG actuator or solenoid. Due to the cat delete and hearing the unit spin, I don't think I have a jammed impeller. No other codes, indicators, or behavior that makes me think its in limp mode. Car runs and (slowly) achieves highway speeds, travels 50 miles a day so no catastrophic failure.

I don't think the mods have caused the problem here, more likely a normal age-related failure in the boost system. I just don't know enough about working on turbos to diagnose this.

UPDATE 3/19: Began diagnostics over the weekend: Removed WG regulator arm clip and moved the WG flapper with no resistance. WG regulator arm resists and moves back when pulled on. Warmed the car and revved to redline with an observer watching the engine, no BOV hiss, no movement on the WG or arm, observer describes "a big puff of air and dust shot out from around top-center of the engine."

WG flapper does not appear to be stuck, WG actuator arm appears to work, WG solenoid inconclusive. No new codes or symptoms. Puff of air escaping with no BOV hiss, no WG movement points to cold side air leak.

Next step is building a smoke tester to find the leak.

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    Boost leak? Have the car smoke tested to check for leaks in the intake system (bring it to a shop that knows Subarus, there's a lot of nuance to look for). If it's been properly modded, it needs a tune for those mods, otherwise you'll risk damaging the engine in short order. Since the car's been running for years, it likely has a custom tune for the mods (or perhaps just an off-the-shelf tune that comes with the AccessPort, which is better than nothing). – Shamtam Mar 15 '18 at 14:12
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    One thing to keep in mind, if the 1psi at WOT reading is accurate, then your problem is not just the wastegate solenoid, as even without any external control, the wastegate mechanically will hold a certain amount of boost. On the '08-'14 WRX and the '05-'09 LGT, that's around 7psi. – Shamtam Mar 15 '18 at 14:15
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    I'd be inclined to have you look at the cold side piping for any tears in boots, slipped boots, or other places it could be leaking. This might involve a complete pull out and inspection of the cold side, to include the intercooler. Considering you have no boost, yet can hear the turbo spooling seems to me you're losing pressure somewhere along the line. – Pᴀᴜʟsᴛᴇʀ2 Mar 15 '18 at 15:28
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    With a non-stock exhaust, I can guarantee the car is running a custom tune on there. If it wasn't, you'd have other problems. I suggest you play around with the AccessPort as soon as you can and learn more about it. It's an integral part of your car and could be helping you diagnose the problem you're experiencing. – Ellesedil Mar 15 '18 at 17:04
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    @SamBasso Regarding the 3/19 update: if you're just sitting in neutral and revving the engine, it won't build boost (and as such, you won't see the WG arm moving at all even when everything is working properly). Assuming all the hoses are good, it's even possible for the stock intercooler to be separating around the end tanks, if high boost has been run through it for some time (possible explanation for the "big puff of air and dust... around top-center of the engine"). – Shamtam Mar 19 '18 at 15:45
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I would guess you have a boost leak. Have the car smoke tested to check for leaks in the intake system (bring it to a shop that knows Subarus, there's a lot of nuance to look for). If it's been properly modded, it will have a tune for those mods, otherwise you'll risk damaging the engine in short order. Since the car's been running for years, it likely has a custom tune for the mods (or perhaps just an off-the-shelf tune that comes with the AccessPort, which is better than nothing), especially since the mods are a large turbo and a larger exhaust.

There is a poor-man's boost-leak test that involves plugging the intake (a pint-sized paint can works well I think), pulling the vacuum reference line to the bypass valve (the small hose), blowing into it, and then covering it with your thumb. After a couple seconds, letting off with your thumb should result in some of the air you blew in escaping back out. If that doesn't happen, you have a vacuum/boost leak somewhere. Alternatively, if you have a leak, you'll hear the air hissing out when you blow into the BPV reference line.

One thing to keep in mind, if the 1psi at WOT reading is accurate, then your problem is not just the wastegate solenoid, as even without any external control, the wastegate mechanically will hold a certain amount of boost. On the '08-'14 WRX and the '05-'09 LGT, that's around 7psi.

  • Updated OP. Any insight on what I can do with the accessport to help diagnosis? – Sam Basso Mar 19 '18 at 15:13
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U have deaf injectors, dead fuel pump, and need throttle body service, tgv deletes, and could use a ecu tune

  • Welcome to Motor Vehicle Maintenance & Repair! Your answer is lacking any real evidence as to why you believe this is the issue with the car. If you could, edit your answer and flesh it out so it actually contains useful information for the OP. Also, check the Tour page and the Help Center as they contain a lot of information as to how StackExchange works and what we consider a good answer. – Pᴀᴜʟsᴛᴇʀ2 Jun 6 '18 at 12:36

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