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Knock sensors


silverton
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So I know this is mostly for turbo's, but... since all of our cars have knock sensors and they kind of have something to do with the cars base tune, here I'm putting it.

 

I have been fighting poor performance and mpg's, 16-19 with mostly highway cruising, in my 2001 LGT for a few years. I even put an equal length header on it and while it helped, all it really did was make more noise with out much more go. Unfortunately the noise was like a brick in a metal trash can rolling down a hill, it's awful!

 

Since I have some experience tuning my home brew 2.5RS+t I did some data logging on the Legacy before replacing the knock sensor last August with an NTK unit. I've always liked NGK so I've always used NTK knock sensors, but there was no change in the cars behavior. Before my 2.5RS was turbo, I know I'd put one of these knock sensors in it with the same exhaust manifold and I remember the same awful noise from the back. I even flashed my 2.5RS' ECM while I worked at the dealership, no one there knew how to do it and I remember it was a pretty janky set up, but I was able to update it. While that helped, the underlying issue was still there, when I turbocharged it of course all that changed and I never revisited.

 

Sorry this is so long, it's almost over. My Legacy over the last month has been real wheird. Intermittently feeling like it's out of gas when it has plenty. HMMM, I had a knock sensor high input code! I go to warranty the sensor, it's only been six months... SIXTY DAY WARRANTY. :spin: Do some more data logging with it and I find the knock sensor is pulling 5-10 degrees, almost all the time, but I obviously can't hear any actual knock out of the motor. so WTF

 

I buy a new Bosch sensor, since it's the only one one with a limited lifetime warranty and it was only $20 more than the NTK. I installed it, reset the ECM, and it's a completely different car with a different sound. It pulls 1 degree very rarely, with most of the time it showing advancing a degree or more. Interesting thing about the Bosch sensor, part of it had been shaved down like an attempt to remove a brand. Does say "unisia jecs" on it so it may have been the subaru..or possibly a nissan logo shaved off.

 

I owned the Legacy during my time at the dealership and had attempted to update its ECM as well, but the time between my impreza and the legacy they had replaced the diagnostics laptops, which were no longer compatible with the old SSM3 bricks. That being said, I think the bit of negative timing I see now could be fixed by the ECM update

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