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Discussion Starter · #1 ·
Hey all. I have a ‘98 OB with an EJ22 swap. Engine has about 160,000 miles. Has been getting increasingly bad mileage after I bought it about 2 years ago. Its now down to about 15 miles per gallon in town. I don’t drive like a madman either. Seems like its running a little rough too. Ive recently cleaned the air filter, sprayed the MAF and its plug with QD contact cleaner, cleaned the spark plug wire connections, and checked that the PCV is working. Clogged fuel filter? Bad anti knock sensor? Any suggestions appreciated.
 

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2020 Onyx
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13,282 Posts
At that age I would wonder about a clogged catalytic converter.
 

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2020 Onyx
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13,282 Posts
I'd wait for someone more experienced to comment as my speculation was only that.
 

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2011 Tribeca, 2005 Legacy GT
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When was the last time you changed the plugs and wires? Change the fuel filter like you said - it’s cheap and easy. Usually these air filters are not serviceable - if it’s dirty and nasty just change it.
 

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'03 outback limited, '01 Outback Limited, '01 Legacy L wagon, '96 Legacy Brighton wagon
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Like jeyping said - change the plugs and wires.
 

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Discussion Starter · #9 ·
If those plugs are okay, I'd do a compression test. There's a chance that your rough idle and poor mileage is from some worn out rings, or maybe even a leaky head gasket... I hope that's not the case, though!!

Good luck, and keep us updated!
Put the fuel filter in and checked the plugs. They looked pretty destroyed. Worn down to the point where the gap was about .060. Replaced with a set of NGKs. Car seems to idle and drive a lot more smoothly. Guess Ill just have to wait to see how the mileage improves.
 

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Discussion Starter · #10 ·
Hmmm, well, unless the gauge is reading wrong through the first quarter tank, it doesn’t look like the mileage increased. I don’t think the head gaskets are bad, since my coolant has stayed constant for about 2 years of pretty constant driving. I do get a pretty strong gas smell blowing through the vents on start up. Maybe clogged catalytic, bad O2 sensor, or bad antiknock? I don’t really want to just start throwing parts at the car
 

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2006 Outback 2.5i manual
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297 Posts
Hmmm, well, unless the gauge is reading wrong through the first quarter tank, it doesn’t look like the mileage increased. I don’t think the head gaskets are bad, since my coolant has stayed constant for about 2 years of pretty constant driving. I do get a pretty strong gas smell blowing through the vents on start up. Maybe clogged catalytic, bad O2 sensor, or bad antiknock? I don’t really want to just start throwing parts at the car
If you're smelling fuel through the vents, it's possible you could have a fuel leak somewhere in the engine bay. I would inspect your fuel filter, all the visible fuel lines, and lastly take a close look at your fuel rails and fuel injectors. I would inspect all of these components with the fuel system pressurized...as in, turn the key to the on position but don't start the car. Do this a few times to make sure it's fully pressurized, then sniff around and take a really close peek.

I had a similar thing happen on an older car and it turned out to be one of the fuel injector o-rings.
 

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Discussion Starter · #12 ·
If you're smelling fuel through the vents, it's possible you could have a fuel leak somewhere in the engine bay. I would inspect your fuel filter, all the visible fuel lines, and lastly take a close look at your fuel rails and fuel injectors. I would inspect all of these components with the fuel system pressurized...as in, turn the key to the on position but don't start the car. Do this a few times to make sure it's fully pressurized, then sniff around and take a really close peek.

I had a similar thing happen on an older car and it turned out to be one of the fuel injector o-rings.
Its not really a fresh gas smell. More like an exhaust smell. I replaced the fuel filter not too long ago, and theres no leaks that Ive found.
 

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Discussion Starter · #13 ·
I checked the anti knock sensor today, looks alright. Cleaned the throttle body, and MAF. Maybe I have bad O2 sensors making the engine run super rich? It sure smells like it
 

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2006 Outback 2.5i manual
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I checked the anti knock sensor today, looks alright. Cleaned the throttle body, and MAF. Maybe I have bad O2 sensors making the engine run super rich? It sure smells like it

Could be! Could also be a clogged cat.

Did you check the knock sensor with a multimeter? Speaking of which, it would be helpful to check your MAF sensor with it as well, and maybe even your ignition coil. Use the FSM to find which pins to test along with the corresponding values.

Is your timing okay? Still might not be a bad idea to check your compression.
 
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