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Discussion Starter · #1 ·
So overall my car has been running great, no reason to complain. Then out of the blue, this morning I start it up, and there is a very obvious misfire. Then the CEL comes on and starts blinking. Then just like that, the misfire goes away, everything is back to normal. The code is a P0301. I know what the code means. What I'm confused about is what can cause a misfire that then just goes away? Intermittent injector? Leaking injector?

The plugs are wires are known to be good upon last checking, I haven't pulled any yet to look at them. I don't see a problem with either causing a temporary misfire.

Look forward to hearing your ideas.
 

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Id wait to see if it comes back, if so, check the obvious, plug, wire, coil and injector. Then, maybe compression and leak-down tests.
 

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Maybe flash over on the external plug ceramic, on a wet dewey, or rainy morning start???

Pull the plug & check carefully for external, or internal cracked, or dirty/fouled creamic insulator.

If thats ok, if you haven't already done so, make sure the plug boot inside & the external spark plug inslator are squeeky clean, then butter on a light film of a good di-electric grease, like (DowCorning, or GE), onto the plugs external insulator & evenly up inside the plug boot, to prevent flash over on those wet dewy morning starts, or rainey days. Make sure the plug boot snaps on securely.

If the plugs & wires look ok, maybe it was an acting out injector as you suspect.

If you think it was an injector problem, maybe consider running the present fill of gas out, then at the pump, add a 20oz dose of Chevrons Techron Cocentrate Plus to the tank, then fill up with Chevron, or Texaco gas to get good mixing.

These two fuels already have some Techron in them, so the 20oz addition will raise the treat rate 10X above that of pump gas.

This will likely be able to tidy up the the injectors, intake valves & combustion chamber in one treatment. Run most of the treated tank out to get the max benifit & let us know how it goes.
 

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+1 on the plug boot, wire, and spark plug ceramic, but also check the coil pack for any cracks, take it off and check the back of it for cracks/burn marks as well.
 

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Thinking about this some more, at idle, you could do a "wet down test" of the #1 plug & wire, with a spray bottle of water, after sundown & look for arcs & sparks, or rough idle, before you pull the plug for inspection.
 

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Not so bad if it's done from underneath!!!???
 

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The rear plugs are easy to get to if you take the upper manifold off. I had the whole job, remove manifold, replace plugs, replace manifold done in less than a hour on my Escape. I know some people say it can be done without removing the manifold but I prefer the access gained by getting it out of the way.
 

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Discussion Starter · #10 ·
The morning was not wet or dewy. It was not particulary cold either.

Plugs, and wires are both new. The problem has not repeated itself.

The plugs, wires, intake gaskets, were all replaced in April. Used Autolite XP Iridium plugs, Magnacore wires, Fel-Pro Permadry gaskets.

I seriously doubt ignition is the source of the misfire.

Ran Techron concentrate though last week. I don't often do that however. I ran some Seafoam through the intake at the same time. It was about a week and a half and about 1000 miles since that was done to the time the misfire occurred. So I don't think they are related.
 

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Don't take the plugs & wires off the suspect list yet, just because they are fairly new. I've seen bad new parts right out of the box, or folks damage them on installation, like over torque, crack or chip a plug ceramic, or damage a plug wire or connector, or not snap the wire securely to the plug or coilpack!!!!

Seeing as how conditions were dry & you don't otherwise suspect the ignition, But you say you did a double dose decarb treatment with SeaFoam through the intake, with Techron in the tank, about a week & a half/1000 miles previous to the miss, which hasn't returned, maybe it was a case of CCDF, (Combustion Chamber Deposit Flaking), as that condition is known to cause intermittent problems!!!!!

During the decarb treatment, did you take it out for the "blow it out with rpm above 3600 for 3 miles", part of Fords decarb TSB, after the SeaFoam dose was ingested through the intake????

Then afterward did you continue likewise, with daily, spirited accelerations, while the Techron was still in the treated tank, to blow out any remaining intake valve & combustion chamber deposits????

If not, imo CCDF would be a good suspect for your list, for what appears at this point to have been a transient happening.

More thoughts for consideraton.
 

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This is typically what happens to me before the coil craps out. Usually I get an isolated incident, like you describe, and then all is well for about 3-6 weeks. Then, usually at a very inconvenient time, the coil craps out completely. (oddly this JUST happened to me on a wet and cold day two weeks ago when the hurricane remnant blew through the metro-DC area, to the same exact cylinder!)

I'd just change out the coil and the plug and move on.

Now if this is a recurring issue on this plug, then that's a whole other story.
 

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Discussion Starter · #13 ·
It has not acted up again.

All the vehicles I had with ignition related misfire had nearly constant misfires, not this misfire for a few seconds clear up and not do it again, thing. I have cleared the code, since the light being on was bothering me. The code has not returned, and I would feel it if there misfire was still there. I guess I will just have to wait till it does something again, if it does.

Interesting ideas though.
 
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