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Old 07-28-2013, 06:56 PM   #1
MikeC5
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Member#: 104702
Join Date: Jan 2006
Location: South Eastern CT
Vehicle:
95 Legacy
Green

Default Misfire Codes

My '02 2.5L is throwing occasional misfire codes. I did go through the FAQ and read through several threads on this issue but many of them don't have a resolution of the problem posted.

About 2 months ago I replaced head gaskets (Six Star) and replaced all gaskets/seals, plug wires and plugs while engine was out. A few days after it was back on the road I got a cel for P0301. I cleared it and it has been O.K. for the last 2 months. Engine light comes on the other day and I'm getting P0301, 2, 3 and 4 plus pending on 1 and 2. The car seems to run fine, idles fine, gas mileage is around 25 mpg which is what it usually is... WTF?

I never saw any misfires before doing HG (in 70K miles that I've owned it). I did adjust valves while heads were off and cleaned up the piston tops and combustion chambers....

I plan to pull the plugs next and see if they look funny.
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Old 07-30-2013, 12:26 PM   #2
MikeC5
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Member#: 104702
Join Date: Jan 2006
Location: South Eastern CT
Vehicle:
95 Legacy
Green

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Pulled the plugs and they looked fine. They are new AC plugs, not NGK and are just plain old single electrode plugs (which had never previously been a problem). The gap was right at 1 mm. I will admit to using Autozone for replacement plug wires (Bosch, I think). I replaced the fuel filter while under there and cleaned up engine/firewall grounds, no obvious vacuum leaks. I tried misting water on the coil pack while running at night and saw no arcing. Driving it to work this morning (40 miles) it ran fine but I did see engine light come on for maybe a second and then off. I read that a blinking light could mean damaging misfires but wouldn't the light eventually stay on?
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Old 07-30-2013, 07:32 PM   #3
MikeC5
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Member#: 104702
Join Date: Jan 2006
Location: South Eastern CT
Vehicle:
95 Legacy
Green

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Light stayed on this afternoon.. Misfire on all 4 plus a pending 0420. You guys are really a great help...
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Old 07-31-2013, 01:37 AM   #4
rhino6303
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Member#: 181314
Join Date: May 2008
Chapter/Region: NWIC
Location: SW Washington
Vehicle:
2005 Impreza OBS SRR
05 Legacy GT RBP

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You are having misfires on all cylinders? I am thinking any of the following to check or check again:

Spark plugs (get some ngk)
Coil
Injectors
Check resistance on plug wires

Are your battery terminals clean and tight?
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Old 07-31-2013, 05:49 AM   #5
MikeC5
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Member#: 104702
Join Date: Jan 2006
Location: South Eastern CT
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95 Legacy
Green

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What should resistance on plug wires be? For the coil, I can swap it out for another one. I don't think there would be much point doing reistance checks since the problem is intermittent (and car starts & runs fine). Battery connections are good. Since this only started happening after an HG and clutch job (engine removed) with new plugs & wires, I'm hoping it is one of the latter two...
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Old 07-31-2013, 05:37 PM   #6
MikeC5
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Member#: 104702
Join Date: Jan 2006
Location: South Eastern CT
Vehicle:
95 Legacy
Green

Default

The Bosch plug wires measure around 800 ohms and the manual says they should be between (roughly) 5k to 12K ohms. I checked one on our other Outback and it measured around 2.5k (non-OEM). I did go ahead and swap the coil with one that I knew worked when removed. We'll see. I may have to bite the bullet and get some NGKs and OEM wires...
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