Intermittent misfire.

cbxer55

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Jan 25, 2020
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4.0 V-6. I don't get it. How can a misfire be intermittent. Most of the time, I start it and it runs great. Every once in a while, most especially after a hot start, it develops a misfire. That it's intermittent means it's not likely the usual culprit of plugs, coils or wires. Has to be something amiss in the computer electronics. Drove it to work yesterday, it was fine. Drove it at lunch four hours later, it was fine. Drove it home two hours later, missing bad. Could tell just giving it some gas. Started it up a while ago, it's fine.

Any ideas?
 
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cbxer55

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Jan 25, 2020
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Coils, plugs and wires were replaced in May last year. I pulled the plugs today, they all look identical. Code is P0300, Random Misfire.
 

cbxer55

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Jan 25, 2020
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I think what may have happened is that when I put the new wires on back when, I didn't put one or two of the wires on the plugs tight enough. When I pulled them off to check them, two came off without making that snapping sound. Made sure when I reinstalled them, that I felt that click, that indicates fully engaged. Problem gone. I guess they were close enough to cause an arc, but yet still not cause an arc occasionally?
 

7991LXnSHO

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I think what may have happened is that when I put the new wires on back when, I didn't put one or two of the wires on the plugs tight enough. When I pulled them off to check them, two came off without making that snapping sound. Made sure when I reinstalled them, that I felt that click, that indicates fully engaged. Problem gone. I guess they were close enough to cause an arc, but yet still not cause an arc occasionally?
A bad connection somewhere making intermittent contact was one of my top two predictions, followed by impending component death. This fits it as well as anything. I hope you used dielectric grease so the boots are sealed from water a bit and come apart without destruction next time.
 
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cbxer55

Active Member
Jan 25, 2020
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Oklahoma
A bad connection somewhere making intermittent contact was one of my top two predictions, followed by impending component death. This fits it as well as anything. I hope you used dielectric grease so the boots are sealed from water a bit and come apart without destruction next time.

ALWAYS! There was no destruction. I put the same wires and plugs back on it. Plugs looked fine. Wires and coils were new last May.