Finally decided to make a post after dealing with this issue for months.
Long story not so short - I bought a legacy gt wagon that was built by someone here on the forum a few years ago. It was built with a blueprinted ej25 and a few mods (listed below). Last March it was sold to someone who may have been a little in over their head and eventually decided that it wasn't the car for them. This is my second Subaru, but my first turbo one. I'm in college so I try to stick to a budget but I'm also not trying to cheap out on this thing.
Engine Mods/specs:
- Remanufactured longblock (about 40k miles as of now) and stock heads blueprinted by a shop (balanced rods and pistons, etc)
- TGV deletes, Catless Uppipe, Cobb Intake, Cobb IC to TB coupler, IAG AOS, Gates Racing Timing Belt, Exedy Lightweight Flywheel + Stage 1 Clutch, DW65C fuel pump, STI FPR mod, Etuned in 2019
- Everything else is stock - namely, stock turbo and boost controller, injectors, downpipe, intercooler, etc.
Problem: I can't get rid of WOT knock. It's enough to be concerning but not enough to show itself. My Cobb AP often shows Feedback Knock to -6 and FKL follows usually to -2.00 or -4.00 in places. It's not consistent. Sometimes it is terrible and my DAM drops to 0.875 or worse. Sometimes a WOT pull reads 0.00 knock. My question is what to do next - I'll list what I have already done below.
Already done:
- Previous owner replaced stock injectors with 750cc Deatschwerks - returned to used stock injectors (not flow tested but cleaned with fuel tank injector cleaner and crudely bench tested)
- All vacuum lines replaced with silicone (excluding the lines running to the turbo; they seem happy)
- Smoke tested intake, fixed any leaks that were present with old rubber lines
- STI FPR connected to BOV vacuum line and manifold port capped.
- Previous owner had the racing version of the IAG AOS installed without getting it retuned (no PCV). I used a kit to adapt it to the street version that retains the PCV valve.
- Bulletproof TMIC Mod. Aluminum C Channel with JB weld just to be safe.
- Car was tuned with a TurboXS 50/50 valve. Returned to stock BPV as it was causing a massive vacuum leak.
- Timing belt was installed with the incorrect crankshaft gear guide which caused it to skip two teeth. Fixed and installed the correct guide (that was a close one...)
- Replaced MAF and front O2. Checked MAP sensor for accuracy. Cleaned the cone air filter.
- Spark plugs were replaced 1 year ago by PO (NGK one step colder).
- Added grounding straps from engine to battery negative
- PO changed from the DW65c to an AEM pump with a much higher flow. Tested DW65c and reinstalled it with two orings.
- Checked downpipe for restriction and cleaned - looked clear.
- Checked knock sensor and all heat shields. Knock sensor torqued to spec and angled correctly - resistance reads in range.
Test results:
- Compression: 140 135 140 135
- Fuel Trims: Hovers between -5 and +4. Adds fuel when in vacuum and removes when in boost, but that isn't always consistent
- Boost: -11psi at idle. Max is always about 16.3psi - car is tuned for 17psi.
- Fuel pressure checks good and holds prime
So what should I do now? Maybe pressure test the intake again? Get the injectors flow tested? Get a downpipe for a wideband O2 and a retune? I have made a few graphs from 3rd gear logs and they haven't really shown anything amiss except for the knock and drop in timing.
Apologies for the lengthy post!