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Change spark plugs, Misfire question.

Old 04-20-2019, 05:44 PM
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Default Change spark plugs, Misfire question.

Hey guys, i had some misfire codes 300 and 304 and 306. I changed the spark plugs and the code went away for about two weeks. Driving home from work cel started flashing for a couple seconds so i knew the misfires were back.

The question is, is misfire back because i used the wrong sparkplugs? I was gonna get copper champions pre gap .035 but they didn't have it and the only other pre gap the store had was bousch platinums pre gap .040.

Should the first step be, plugging the spark plugs and checking them out and replacing them with the copper champions?
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Old 04-20-2019, 06:39 PM
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You should pull the plugs to check the condition. For example, running rich due to a failing O2 sensor could foul plugs, leading to misfires, and new plugs could make that go away for a short period time, and then return.

Also, every auto parts store I have ever visited sold very inexpensive spark plug gappers. They usually have those coin looking ones for around .99 as impulse buys near the cash register. You can and should gap (or at least check the gap) on your own plugs. Never trust that the factory got every plug correct.

Even if they were "pre-gapped" a prior customer could buy them, alter the gap, and return them later for whatever reason (like realizing their existing plugs were in better shape than they thought). If the box is in good condition, the store might put them back on the shelf.

Last edited by jordan96xj; 04-20-2019 at 06:42 PM.
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Old 04-20-2019, 08:33 PM
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I wouldn't assume you need to replace the plugs. While Champions are preferred, I wouldn't expect Bosch Platinum to give you misfires. Maybe, but... I'd be looking elsewhere, first. Straight off, I'd re-gap them to .035, as Jordan suggests, then start looking for the real problem.

I'd be looking at your grounds, first, to make sure you are getting a GOOD spark. Spark is good, but good spark is better, and a weak spark can be due to a failing coil or to poor grounds.

What year is your beast? It helps us to know so that we don't point you in the wrong direction. For example, if you have a later model with coil packs, my comment about a failing coil doesn't make much sense. Or maybe it would if I had said, "coils".

Last edited by BlueRidgeMark; 04-20-2019 at 08:43 PM.
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Old 04-21-2019, 12:17 AM
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  • I have a 2001, i will be able to pull the plugs Monday
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