For the past few months, the check engine light on my Outback wagon has been coming on. It stays on for a couple of days and then turns off for a couple of days. I got my oil changed yesterday, and they checked the codes for me. Apparently my knock sensor is failing. I've read some of the threads on this, and I will attempt to replace this myself.

 

I'm wondering if this could be affecting my mileage? I figure I've been getting about 16 mpg for a while. This seems to be pretty bad. The guy at Oil Can Henry's also thought I needed a new fuel filter. Of course they want to upsell me as much as possible, but I figure I should attempt to change that as well. Should I check my spark plugs too?

Welcome aboard Bill. Yes, you can replace the knock sensor yourself. Not too difficult at all, just follow what the threads tell you. By the way, if you check online or even on ebay you can save quite a bit over dealer pricing for the KS.

 

How many miles on the car? How many since it's had a tune-up? New fuel filter & air filter are probably a good idea. New PCV valve and clean the hoses connecting it. New plugs (use NGKs) and new plug wires (use OEM or possibly NGK--but no cheapie aftermarket) may help a lot, especially if it's been awhile.

 

Good luck!

It has 188,000 miles or so. I bought the car a year and half ago from a guy who rebuilt the engine. I guess that was the last time it was tuned up. How often do spark plugs need to be replaced? I think they are less than two years old.

I just installed a knock sensor that I bought on ebay from this seller: http://myworld.ebay.ca/chandlermotorsportsinc for about $16cad shipped to my door. Works perfectly so far and cleared up a surging/hesitation/bucking my 98 Impreza was having.

I just bought a knock sensor from ebay for my 90 legacy for 13.00...if you don't mind waiting a couple days, ebay is worth the savings. Autozone had them priced for 45 or so.

It has 188,000 miles or so. I bought the car a year and half ago from a guy who rebuilt the engine. I guess that was the last time it was tuned up. How often do spark plugs need to be replaced? I think they are less than two years old.

 

Might be a good idea to pull the plugs and inspect them. Should be okay at two years--but who knows?!! (If I were going to pull them, I'd probably just replace them anyway!)

 

See if you can identify the brand of plug wires. If they're some aftermarket brand, I'd replace them with OEM or NGKs--Subarus can be real touchy about the wires.

 

Good luck!

Knock sensor: Buy a used one if you've got a yard that sells parts nearby. Uncommon for the '95+ years to fail.

 

Fuel filter: I'd change it. Not difficult technically, but those darned hoses are a pain to remove. Let the car sit overnight so there's little/no pressure on the fuel lines.

 

Spark Plugs: The EJ25 should have platinum plugs, per the owner's manual, which are good for 60K. Pull one to check. If they're not NGK platinums nor NGK coppers, I'd change them to one of those. And 'ditto' on the wires - get the NGK brand.

 

Your MPG should be closer to 20 around town; 27 highway, from my experience w/a couple different OBs.

 

GL,

Td