Cylinder #2 COP Keeps Failing - Lightning Forum | LightningRodder.com
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post #1 of 16 (permalink) Old 04-19-2017, 09:05 PM Thread Starter
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Cylinder #2 COP Keeps Failing

Hi, I've been lurking here for years, never really posted much. But, I've recently run into a problem that I'm hoping someone will recognize...

About a week ago my truck died, I found that the 30amp fuse under the dash was popped and that the coil on the #2 cylinder had failed. I replaced the fuse and COP and was able to get home (about 200 miles).

When I got home I went ahead and replaced all COP's and Plugs. I took truck for a quick test drive only to have the 30 amp fuse and COP on #2 cylinder fail again (overheated and boiled fluid in COP)

At this point, I suspected a grounded coil plug, but I can't seem to find one.

Since then, I've swapped plugs, COPs, hooked up an O-Scope... And everything is fine until I take the truck for a test drive. I put truck in gear and pull away, and it will start to stumble, ending up in a blown 30amp fuse and failed Cyl. #2 COP.

Besides a shorted COP ground wire, what else could cause this?

Thanks,
Jason
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post #2 of 16 (permalink) Old 04-19-2017, 09:34 PM
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Check your pigtail with a volt meter.

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post #3 of 16 (permalink) Old 04-20-2017, 08:38 AM Thread Starter
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Voltage was consistent across every COP plug I checked (nothing unique about #2)






Resistance was consistent across every COP plug ground I checked (~619 Ohms), no ground found.


Then again, I can put a new coil on the truck, and let it idle for a half hour and all is fine, I can wiggle the harness, move every connector and wire I can find, and it will idle (and rev) perfect. As soon as I take it for a ride, it will stumble and the coil will pop... I must have a wire that grounding out due to a harness movement, right?
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post #4 of 16 (permalink) Old 04-20-2017, 09:01 AM
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Its interesting that it only does it during driving. Could it be the ECU?
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post #5 of 16 (permalink) Old 04-20-2017, 09:16 AM
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Saw repeated coil failures on a GMC Envoy, it would actually melt down the cop and blow the fuse, also wiped out cat. turned out to be the ecu!!! never saw such a thing on a Ford but anything is possable!!!!!! any codes or check engine light????
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post #6 of 16 (permalink) Old 04-20-2017, 12:18 PM Thread Starter
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No codes are showing up at all...
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post #7 of 16 (permalink) Old 04-20-2017, 12:24 PM
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Im still thinking ECU
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post #8 of 16 (permalink) Old 04-20-2017, 12:33 PM
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Sounds like a driver chip in your PCM (ECU) is bad - the circuitry for these things is that they provide constant 12 volts to the coil and trigger the ground side to pulse the coil. If the driver chip in the PCM shorts, it'll pull a constant current draw through the coil and eventually blow the coil and the fuse also.

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post #9 of 16 (permalink) Old 04-20-2017, 02:34 PM Thread Starter
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Is there anything in the PCM that would allow it to output a normal signal at idle and free revving and then short out under load?
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post #10 of 16 (permalink) Old 04-21-2017, 05:17 PM
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Low RPM=slower charge/discharge rates.
Higher RPM= a higher charge/discharge rate.

The easiest way to burn out a coil is to not let it to completely discharge
in between cycles.

A too wide plug gap or damaged plug?
Switch the spark plug to another cylinder to test it.
If problem switches, it was the plug.
If problem stays, you have eliminated the spark plug anyways.

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post #11 of 16 (permalink) Old 04-21-2017, 09:15 PM Thread Starter
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Quick update, I bypassed the harness and ran a new wire from the coil ground to the PCM connector. And, so far, truck runs fine... (Not eating coils anymore)

I'll dig into the harness tomorrow and see if I can find the short.
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post #12 of 16 (permalink) Old 04-22-2017, 09:23 AM
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coil failures

Not discharging the coil completely. The charge builds up to where it penetrates the insulation on the windings.

To kill a race coil on one of the older motors, just unplug the coil/distributor wire and crank the engine without allowing the charge fire.

It only takes two revolutions....

https://www.reference.com/vehicles/c...4dc5a917271554

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post #13 of 16 (permalink) Old 04-30-2017, 07:50 PM Thread Starter
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Last update. It was wire abrasion in the harness between the PCM plug and the large plug that goes to the coil harness.
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post #14 of 16 (permalink) Old 05-02-2017, 09:48 AM
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post #15 of 16 (permalink) Old 05-02-2017, 11:04 AM
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Great work!!!!! a lot of so called pros would not have found that before changing unnessary parts!!!!!
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