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Old 03-21-2005, 07:20 PM   #1
Scooby Newbie
Member#: 83449
Join Date: Mar 2005
Location: Sudbury, Ontario, Can
2000 Impreza Outback
2 tone green-grey

Default PO302 Misfire Code - Problem Identified

Just had my car (00 Impreza Outback Sport) scanned for the misfire code. The scan indicated a misfiring on no.2 plug. After some short searching, teh mechanic noticed the plug to have a carbon deposit along the porcelain from the top of the plug to the nut. The carbon is a result of a bad plug wire, causing the spark to arch from the tip at the wire connection to the nut. The carbon deposit, being highly conductive, increases the rate of arching and as a result, increases the misfiring.
With my car, it does not seem to misfire under light acceleration, which it actually might be doing but not noticeable due to the light load. However, when accelerating hard, it misfires noticeably and constantly at almost any rpm. Anyways, since he did not have new wires available at the time, he did clean the carbon from the plug and the car run better. Coincidence?

Interested in any thoughts!
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Old 03-21-2005, 07:51 PM   #2
Scooby Specialist
Member#: 54942
Join Date: Feb 2004
Chapter/Region: South East
2004 WRX


It will run better, but only temporarily. The carbon track on the porcelain is matched by a track on the inside of the rubber boot, too...it'll start up again. Replace the wire and either clean the porcelain well, or just replace the plug, at the same time. I'd replace all four plugs & wires, if one was carbon-tracking.
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