Melted wire harnesses on v6 coils

I have a 2005 v6 tacoma pre runner with about 151k miles on it. Last week it misfired a lil on cold start up then a few days later threw a cel. I scanned it on my obd scanner and it was a #4 cylinder misfire. I changed out all the plugs with Denso toyota plugs gapped to .41.

But when i tried to disconnect the wire harness to the coil on cylinder #4 it was melted to the top of the coil and it wouldn't disconnect. All the other wires that connect to the other coils were ok. It was melted so bad i had to use a knife to cut the wire harness from the plug. Now the truck has a cel on cylinder #4.

What would cause it to do that?

And how can I fix the wire harness? Do I need to

 

Sorry for the lighting. It happened after night fall just now. See how the wire harness from the engine is melted to the coil. I looked at the coil and its fine, only the wire harness is melted.
This ever happen to anybody before?
And wouldn't putting some dyelectric grease solve the problem?

I'm thinking about putting a new coil in tomorrow to see if it helps.

 

The engine harness is big and all one piece. $1400 CDN new from the dealer when I asked the question a few years ago. If the melting was from overheated wiring inside the plug then you had a major resistance problem. Maybe check wrecking yards for a pulled harness or at least that part of a harness that you could splice in.

 

looks like someone broke the clip and put silicone on it to hold it on
i do that when they break

 

Cut old solder and heatshrink new. Or if you are lucky depin old wires and push pins in a depinned plug from junkyard.

 

That doesn't look good

 

I can take a pic from the inside. I looked at it from the inside and it didn't look burnt out. Its only happening on the outside. But now its starting to misfire again. Im thinking if splicing in a new plug from the junkyard and putting dyelectric grease on it. When my resistor for the fan speed blower went out a 2nd time i applied some more grease then the dealerships did the 1st time and it works fine now. Hopefully I can

 

You can't just replace that one connector. You'll have to buy a whole new harness which will cost over a thousand dollars. If the connector is still useable and seats properly, try replacing the coil to see if that fixes the issue.

 

O ok. I didnt know that. I will replace the coil tomorrow and see. Hopefully my dealer will have it in stock.

 

Wait before you buy a new coil, take the current one out and replace it with the one next to it. If that solves the issue, bam the coil pack is the culprit.

 

That's what I was thinking about doing but I had to drive almost 100 mi before the cel and misfiring happened again.

 

Hmmm, it's up to you then. If you have the funds, go ahead and replace the pack and see what happens. I would still try switching the packs around to see if that's the issue. I'd hate for you to spend money on a coil pack to find out the wire harness is what needs replacement. It could be both, but the coil is the cheaper of the two. It's your call, but I would rather save a few bucks over throwing parts at it.

 

But he may burn another connector doing that...

Dielectric grease is not a cure. I don't know what you know about dielectric grease but it is an Insulator and will not cure a high resistance connection.

Dielectric grease is to keep out water and seal a connector used in harsh environments.

You should use some but only on the sealing area of the connector.

 

True, I didn't think about that. I don't know what else he could do. If he replaces the coil pack and the connection burns up again, he will be in the same situation. Maybe he should take it in to a shop who can better diagnose the issue. Too many factors are in play here to begin with.

 

I just did my plugs, and broke a clip. Seems to hold on it's own.

Why do these threads pop up when I finish a job??

 

I didn't realize the coils cost so much lol. I bought the truck new and have always had it serviced by the same dealer so I know its not abuse from a previous owner or poor maintenance. I have seen coils burned out and have replaced them on other makes but never the harness. I was thinking the wire melted because the truck overheated but its winter time now and I get the radiator flushed every 50k. I will replace the coil and report back. If that doesn't work then I will just replace the harness. Sucks cause it cost alot but I have emissions where I stay and with a CEL I can't get a tag.

 

Why would you replace the harness when part numbers for the connector body and wire pigtails to repair your harness properly were posted by caribe makaira a couple posts above? Have your dealer order the parts, splice the new wire pigtails to your harness using double-wall heat shrink, and replace the coil pack. At least that's what I'd do.

 

So it can be spliced in??

 

I read by another poster this couldn't be done. I could get one of my mechanics to do it.

 

Should I replace the coil first or the connector body and wire pigtails? I figured since all the coils were ok and in the same condition including cylinder #4 putting a new coil in wouldn't fix the problem and probably damage the new coil or throw another CEL.