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.
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
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.