MIsfiring 1997 Outback

Our 1997 Outback, 2.5L twincam, has started throwing up "check engine" lights with the error codes just saying it has detected misfiring in
cylinders 2 and 4. No further clues as to cause of misfire. When it is driven there are occasions when indeed it seems to be weak, but if I really push it it responds and after I "blow out the gunk" it will work nicely for a while. If I clear the codes they stay off for a while, I think it is not supposed to repost them until it has been driven something like 50 miles with repeated faults, but eventually they come back. I have looked for any obvious loose hoses, wires, etc., on the left (driver's view) side, where those cylinders live, as well as searching around for other possible causes. Before I really take everything apart, are there any causes that seem to come up frequently with these symptoms? (It had new timing belts, pumps, seals, etc., not too long back. It had a compression leak in the head gasket that got fixed, on the other side of the engine. I cannot find any connection between work done and the present symptoms.) Thanks! Bob Wilson
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I think there is a coil shared by those cylinders.
Carl
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Hi Bob, Lucky!
On Mon, 23 Nov 2009 10:42:17 -0600, "Robert L. Wilson"

Well, I started to chime in with "Replace the plug wires", but then you _did_ say "twin cam" . . .
Don't the DOHC motors have the distributed ignition (whatever ya call it) where there is a separate module for each cylinder? Don' know.
Bob, if it has plug wires, try a new set. Maybe try another coil pack; sometimes they get weak.
What else might cause that?
Knock sensor going bad? These are easy to replace, and not terribly expensive at a salvage yard.
You've had the timing belt serviced lately? One tooth off on any of the pulleys can cause the lack of power symptom (plus poor fuel economy . . . Been there with an SOHC 2.5l motor).
I would think you'd get a code if you had a flat-out injector failure, but it might be worthwhile to run a can of injector cleaner thru the car.
Same thing for the O2 sensor(s); I think you get a code if there are issues, but maybe not. These are semi-expensive, and kind of a pain to service. I think the first one controls the EFI.
Maybe clean the AFM if so equipped. At some point, the AFM was replaced by a MAP based system, but if you have an AFM, it's probably worth tying to clean it.
This is one of those times where having an OBD-II reader with data logging capabilities might be useful; see if you can "catch" whatever air/fuel/ignition glitch is triggering the "misfire" code. Fix that and you might get your power back, too. I have used an ElmScan tool with good results, and there is a lot of software available for it; both commercial, and freeware. http://www.scantool.net
Hope this is enough to get you started.
ByeBye! S.
Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101
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