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Simultaneous misfire on a pair of cylinders? N/A 2.5L

My 2003 Forester XS, 15k miles, just issued an apparent simultaneous P0301 & P0302. Misfire on 1 & 2. I web searched and the closest I found was someone reporting a simultaneous misfire on 3 & 4 on NASIOC (I think for a WRX). They think it was caused by going to high revs too soon. Mine seemed to occur coincident with high revs just after a warm start (entering traffic). It hasn't come back, but then I haven't given it much time.

As simultaneous misfires a common Sube thing? Any thoughts? The car is running strong & smooth.

Reply to
David
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then I haven't

This is just a wild-assed guess...

The way the coil pack works is that one coil is shared by 2 plugs. The current has to travel through both plugs and plug wires every time one plug fires. Seems to me that an intermittent plug or wire problem might cause a simultaneous misfire, assuming that the two missfiring cylinders are on the same coil.

Reply to
Jim Stewart

Thanks! I wondered what was shared between 1&2, and 3&4. That sounds very likely. If it returns, off to the dealer, else I'll ignore it.

Reply to
David

Note that my description above is not totally accurate.

Even though one coil is shared by 2 plugs, they don't "light the fire" at exactly the same time. At the instant that one plug fires on the compression stroke (and lights the fire), the other fires into the exhaust stroke. An intermittent wire or plug still might cause your problem though.

Let us know what you find out.

Reply to
Jim Stewart

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