First off, I have been all over the forum, and I have looked at all the misfire/turbo problem threads that seem to be relevant. None of them appear to match my issue. I'm looking for some help
I have the 4000 rpm knocking and power loss issue that I have seen frequently in the misfire threads, but I believe my case is different because 1. It's not throwing codes, misfire or otherwise, and 2. It's completely stock. It idles smooth and runs fine until you put a load on it and bring up the RPM.
Here's what it is and what I have done:
2003 wrx sedan, completely stock. I bought it new in December 2002. I personally put every one of its 212,000 miles on it, and no one has ever worked on it but me.
Cleaned the MAF
Replaced the fuel filter
Measured the fuel pressure. I didn't write it down, but I think it hovered right around 35 psi
Ran a couple bottles of Chemtool through it
Replaced the spark plugs. The old ones showed signs of being really old, but that's about it. No fouling
Attempted a compression check, but gave up after an hour of trying to thread the adapter in
Looked for intake leaks. Found none. I even ran an unlit propane torch over it and listened for an idle change, to no avail
This may or may not be useful information:
I have monitored the spark advance with my Scangauge 2, and it doesn't retard significantly or suddenly when it starts its little tantrum at 4000 rpm
The boost indicated on the Scangauge has always been all over the place and reads very slow so I don't trust it very much, but before I did an ECU reset (disconnect battery, run brake lights) it showed way high boost (22 psi) and after the reset it shows very low. It sounded and felt the same before and after the reset so I don't think it really changed.
It overheated a couple times recently due to a cracked radiator (now replaced)
I unplugged the boost solenoid just to see what it would do. While it had much less power, I think I was still hearing a little turbine whine. It did not, however, stop and hesitate when it hit 4000 rpm.
The only thing I can come up with is a bad wastegate actuator or something related. I'm pretty lost.
While I am pretty mechanically adept(I operate and work on farm equipment), I am lost in the world of turbochargers. I would greatly appreciate any assistance.