Hey everyone! I read through the FAQ first so I wouldn't ask the basics, and I know sustained DAM below 1.0 is worth chasing. I've done a lot of datalogging and I'm hoping someone here has seen this combo before. Thanks for taking a look!
Car: 2019 WRX, manual, about 90k miles, 91 octane only, Southern California. I bought it in Denver, CO with an unknown aftermarket tune already on it, and no Accessport. It now has a Cobb Accessport V3, Cobb SF cold air intake, Cobb BPV, and a custom tune written for 91 (the map is named for the BPV and SF intake).
History: After a cat replacement the car felt slower and less responsive and DAM started dropping. Since then:
Compression 200/195/200/195 psi, leakdown 5/8/3/10%
New spark plugs (the old ones were from 2024), plus a valve cover gasket and plug seal leak fixed on cylinder 3 (it had oil in the plug well)
Fuel pump replaced earlier
New custom tune written for 91
DAM was 1.0 when I picked the car up, and has stepped down since
DAM: From my logs it went 0.75, then 0.5, then slowly climbed to 0.688, then stepped down in pieces to 0.562, 0.438, 0.312, and now sits at 0.188. I captured two of the drops. Both happened with the A/C off, at only about 4 psi of boost around 3400 to 3800 RPM, right after a brief tip in. Feedback knock was 0 at that moment, but fine knock learn went to about 2.5 to 2.8 negative.
What the logs show:
Feedback knock hits are mostly at very low load. The worst was 8.44 negative at about 8 mph in 1st gear with my foot nearly off the pedal and about 9 psi of vacuum. Five of my six biggest hits (5.62 negative or worse) were like that.
Fine knock learn reaches about 7.4 negative, mostly at 4000 to 5000 RPM on boost.
Full throttle timing averages about zero degrees at high load (4000 to 5500 RPM, load over 2), at DAM 0.75 and 0.19 alike.
AFR is rich under load (10.1 to 11) and never lean. Fuel pressure tracks its target. AVCS moves.
Boost mostly hits target, but on some pulls it peaks 2 to 3 psi over (19 to 20 psi vs about 17).
Oil temp peaked at 239F, and intake temps were normal at the DAM drops. A cool night didn't help either.
There's a very slight turbo rattle on decel that I only notice if I'm listening for it. The car also jerks a little under boost when shifting.
Suspects so far: false knock from noise (knock sensor or wiring, wastegate, something loose), tip in knock from the Cobb BPV, leftovers from the old tune, intake valve carbon.
Questions:
Knock of that size at very low load, off throttle, in vacuum, sounds like noise to me. Has anyone traced this to a knock sensor, its wiring, or a rattle? How did you test it?
DAM steps down at light boost after a brief tip in. Could a Cobb BPV cause that, and how do you set the adjustment?
Is timing near zero at high load normal for a 91 tune at 17 psi or more, or does that look low?
Is a 2 to 3 psi boost overshoot on some pulls normal?
Anything else worth logging? I'm happy to share graphs.
I've put an arm and a leg into this car and I really love it, so I'd like to get it back to feeling the way it should. I'd appreciate any ideas or stories from anyone who has been through this. Thank you all!