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Old 09-17-2013, 11:16 AM   #1
tdfuller
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Resolving A Slight Engine Misfire?

2002 Ford Focus SE - Zetec 16 Valve DOHC - 89,500 miles:

For the last five days: has had an occassional engine misfire during accelerations and sometimes during idle.

What are some of the usual culprits?

I don't see anything under FAQ/Archives, here are some details:
  • I replaced the plugs and plug wires with Motorcraft yesterday (first time) which greatly reduced the frequency and severity of the misfires but has not eliminated it.
  • Two weeks ago I replaced the fuel filter with a Motorcraft
  • Two weeks ago I changed transmission fluid, filter, and filter gasket
  • Two weeks ago I thoroughly washed the car, including the engine compartment, being careful not to spray the air filter housing, fuse box, and battery. The manual doesn't say to cover the spark plug covers. I found some water dribbling out of at least one of the old spark plug covers when I removed it from the top of the plug!
  • The old plugs definitely had some moisture, some gunk, and quite a bit of corrosion that was likely contributing to the misfire.

I filled up the Focus with a full tank of gas five days ago, just before the misfires started at a different gas station than I usually go to -> Is it possible in 2013 to still get "bad" gas that can cause misfires?

Should I go ahead and replace the ignition coil?

Thanks for any tips.


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Old 09-17-2013, 11:51 AM   #2
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my SPI was misfiring bad for awhile, like, couldn't accelerate at all due to it. I had replaced the plugs and that fixed it greatly, but the ultimate culprit ended up being the coil pack. check for cracks on it, etc, and you will know. don't do what I did and take it in, it's a super easy fix, and cheap if you can find a used one in a scrap yard/ebay. literally unscrew it and unplug a few things, and reverse to put it back in. this should help, and if not, the problems will be worse, but atleast youll know
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Old 09-17-2013, 01:47 PM   #3
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my SPI was misfiring bad for awhile, like, couldn't accelerate at all due to it. I had replaced the plugs and that fixed it greatly, but the ultimate culprit ended up being the coil pack. check for cracks on it, etc, and you will know. don't do what I did and take it in, it's a super easy fix, and cheap if you can find a used one in a scrap yard/ebay. literally unscrew it and unplug a few things, and reverse to put it back in. this should help, and if not, the problems will be worse, but atleast youll know
Thanks. I have had no warning or no check engine light. But, I'll have my eye on the ignition coil pack. I may wait until I burn through my current tank of gas though, to make sure "bad" gas was not a contributing factor. The 3-wire pigtail connector coming out of the ignition coil pack will be checked. It looks ok, but I am going to wiggle it while the engine is running to see if that might be an issue as well.
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Old 09-17-2013, 02:32 PM   #4
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Moved to General Technical Chat.
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Old 09-17-2013, 02:51 PM   #5
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Thanks for the move to technical.
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Old 09-17-2013, 07:44 PM   #6
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My bet is on the coil, too. 4 T25 bolts, a wiring harness, and 4 leads, and you're done.
If you're lucky, none of the bolts are seized, or were stripped by some hamfisted fool trying to change it earlier.
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Old 09-17-2013, 09:11 PM   #7
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My bet is on the coil, too. 4 T25 bolts, a wiring harness, and 4 leads, and you're done.
If you're lucky, none of the bolts are seized, or were stripped by some hamfisted fool trying to change it earlier.
I've had the Focus since new. So, the coil assy should be factory installed.
I am going to wait to burn through my tank of gas, in the unlikely possibility that "bad" things in the gas were contributing to misfire since the time of last full refill seemed to coincide with misfires.

Also, I resolved a non-working trunk bulb today. It was traced to a wire break at the bend in the left side of the trunk grounding the circuit. Since those wires were repaired, it seems like the misfires are almost completely gone and when they do occur are very slight.

I'll post more developments when they occur.

Thanks for the tips.
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Old 09-17-2013, 11:33 PM   #8
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highly doubt anything with the trunk lighting would have much to do with the engine ignition, but who knows. Maybe just a lucky coincidence, mine went away for awhile after I gave her some WOT therapy
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Old 09-27-2013, 06:03 PM   #9
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PROBLEM SOLVED!

Got the coil assy and replaced it. All misfires are gone and the Focus is running as well today as it did new 11 years ago.

... By the way, when the part was en route, I ran to Advance Auto and used their OBD code detector. It said "misfire cylinder 2." Since I had already replaced the plugs and wires, I presume that was the ignition coil for cylinder 2 and I guess the code machine will not say, "you have a bad coil assembly."

When I took the old coil pack assy out, and flipped it over, there was a hairline crack extending along the side of the base with the same side as the plug for cylinder 2. Not sure if that had anything to do with the old one failing.
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Old 09-28-2013, 01:23 AM   #10
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Yes, it did.
You'll get random misfire codes, then eventually Ignition Coil Module A (or B, C, D, E). So it will tell you, eventually.
Make sure to check that wiring harness, especially the middle wire, for problems...otherwise your expensive new coil might start throwing codes within a week or two and you might think it's defective.
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