98 Forester missfite

[milracing]

Misfire that set trouble code for cyl#3 missfire. It felt like maybe the fuel pump; worse under load and sort of going flat. At 266k I figured the pump was worth doing any ways. That didn't fix it but replacing the cool did. Immediately 100% better and running perfect. Drove it for four days. It a bit of trouble.

 

Today, I turned the ac on. The miss as it was before was worse with the ac in. I figured it was just the increased load. Well, with the ac on the miss returned. Not as severe but not good. When I turned the ac back off the miss remained but to a lesser degree.

 

This is a high mileage car but it's in excelent shape. I had the heads rebuilt a year ago.

 

Any ideas?

Thanks!

[montana tom]

Replace your spark plugs with NGK's  replace your spark plug wires with quality parts and finally check your cold valve adjustment.

[Rooster2]

Replace your spark plugs with NGK's  replace your spark plug wires with quality parts and finally check your cold valve adjustment.

ditto as written above. Pull out the spark plug on cyl 3, and see what it looks like. A good idea to have a new set of spark plugs on hand and available for installation.

[milracing]

Plugs are NGK and plugs/wires as a year old

[montana tom]

Check compression and check cold valve adjustment,  Switch plug wires around  see if miss moves.

[milracing]

Ok cool. I'll do that

[idosubaru]

Plugs are NGK and plugs/wires as a year old

 

unlikely older gen Subaru's, EJ engines are not forgiving with average or low grade wires.  i've seen brand new wires off the shelf cause misfires on EJ engines.  best to have Subaru, NGK, or another quality brand.

 

swapping the plug wires should tell you if it's the wire.  the other cylidners are't having issues so presumably those wires are "known good" - put one of them on cylinder #3 and see what happens.