I have a 96 Legacy EJ22 thats mileage dropped to 21 mpg and that gave an intermitent check engine code. I had it read and it was the knock sensor which I replaced w/a JECS sensor. It ran great for about 3 weeks then the fuel mileage dropped again so I replaced it and the new JECS sensor lasted a week with the fuel mileage dropping off again. I replaced it with another sensor (different manufacturer) and the mpg's were never normal. The engine sounds normal through all of this and I just can't figure it out. I only had the one check engine light in the beginning and none after that. Any help would be greatly appreciated.:-\

Try going with OEM Subaru parts? It may be costly but you won't have any issues later down the road.

Yea, I don't think all knock sensors are created equal. I replaced one on a 98 with phase l from Autozone, and it continue to works okay. Try an OEM from Subie, bet that will be a final fix.

Also, be sure to install correctly; clean the threads in the engine block and the surrounding surface, torque the new knock sensor correctly, and route the connecting cable exactly as specified.

I have a 96 Legacy EJ22 thats mileage dropped to 21 mpg and that gave an intermitent check engine code. I had it read and it was the knock sensor which I replaced w/a JECS sensor. It ran great for about 3 weeks then the fuel mileage dropped again so I replaced it and the new JECS sensor lasted a week with the fuel mileage dropping off again. I replaced it with another sensor (different manufacturer) and the mpg's were never normal. The engine sounds normal through all of this and I just can't figure it out. I only had the one check engine light in the beginning and none after that. Any help would be greatly appreciated.:-\

 

If you didn't get more CELs after replacing the Knock Sensor, then that probably isn't the problem.

 

Many things contribute to fuel milage......including the blend of gasoline which changes thorughout the year.

 

IDK.....knock sensors are pretty simply things......I highly doubt you've had 3 bad outta the box knock sensors. Espescially when there are no codes.

 

Something else is up.

 

*note* if you suspect the Knock sensor is being to sensitive, and pulling back the timing too much, try relocating it to one of the bolt holes on the top of the bellhousing. this moves it further from the crank, reducing the sensitivy somewhat (further isolated from source)

what GLoyale said - if the code didnt' come back i doubt 3 sensors are all causing the exact same problem.

 

Knock sensors are supposed to be installed ina very specific way - details and pictures in other threads here.

 

Sounds like you just need a tune up - plugs, wires, air filter - what's your mileage and condition of those components?

 

and - the wires should be Subaru only, this engine is not forgiving on those.

Thank you for all of the helpful tips and I will let you know how things turn out.

I had to replace the knock sensor for both of my RS and I don't have any issues with them yet. I only order OEM because I get it the next day and less expensive.