engine knock under heavy load and low RPMs

[pickler]

I have an 09 impreza with a naturaly aspirated stock 2.5l SOHC engine with 10:1 compression. Engine is rated at 170hp at 6000rpm and requires only regular 87 octane. I have been noticing hesitations with this engine at around 2500 rpm under load. After some data logging i noticed severe knock corrections at those RPMs. I personally don't hear any pinging or detonations (i have excellent hearing). Above 3000 rpm car pulls fine with no reported knocks. Enriching the mixture and using 94 octane gas hasn't solved the knocking issue. I'm wondering how i can go about and figuring if this is a knock sensor issue (false knock) or just a bad engine. Engine has 50k miles.

Logs:
testing temprature 70f, humidty 60%, altitude 700ft, 91 octane gas

https://docs.google.com/file/d/0B3d0m8bScGepQnk5QmNZZmRhZGc/edit?usp=sharing

https://docs.google.com/file/d/0B3d0m8bScGepWHdWS3drcnREWWc/edit?usp=sharing

 

[MikeHalloran]

Do a compression test.

I think you're losing an exhaust valve.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

If you rev it to 2500 in neutral, parked ,controlling the "throttle" by hand under the open hood how does it sound?

I unexpectedly picked up what felt like 20 HP after removing a barely rattling heat shield on a '85 Volvo 240 that had a crude non synchronized knock sensor in its Bosch motronic system. I assumed the rattle was annoying the knock sensor, even though I would never have expected the sensor to feel it.

 

[pickler]

I'm not sure but i think my car is equipped with 3 types of knock sensors for different frequencies (i could be wrong). Either way I drove today with my windows open and while climbing a hill i think i heard knock it was like tick-tick followed by another tick-tick in quick amount of time. Then the sound went away and I continued to struggle climb the incline 4th gear at 2500 rpm. Checking logs, there was 5 deg of timing pulled.

I do have a noisy heatshield. The dealership is supposed to fix that this coming tuesday. A rattling heatshield only causes knock noises under load? Engine is quiet in idle or revving it at idle.

 

[pickler]

it seems to get worst the hotter the engine oil gets.