Update the computer or change cops and plugs

[Trainmaster]

I don't know the resistance but the problem with quality coils seldom lies with high resistance but with insulation leakage, which would be difficult to test.

Remember plug wires? You'd put on the cheap $6 wires, open the hood at night and it would look like Star Wars down there there with all the arcing. A bad coil often arcs to ground, builds carbon tracks and shorts on the secondary side instead of sparking the plug. You're not going to read that with a meter on the coil.

That's why it's important to change the boots. They can carbonize and permit the spark to short to the head.

The Chinese replacements are another story. They just go on fire or melt.

 

[1955moose]

Wasn't that cool though. Grab your buddy's and about 6 beers in you, and ooh ahh! Who cares it bucked like a rodeo bull! As far as resistance primary side is generally .8 to 1.5 thousand ohms, secondary 8-12 thousand. You can look up exact specs but that's safe for any coil, whether old style round tube or Cops. Coils are coils, they all do the same job, supplying spark to plug!

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[Habbibie]

I'm sorry OP I didn't read through the whole replies but does the misfire occured under hard acceleration or its truly just random regardless of throttle input? I been through both symptoms with my expedition but they both took me a while to figure out and I just want to direct you in the right direction on which of the two you're having!

 

[1955moose]

He doesn't say, but is concerned about his daughter driving over 100 miles. It's intermittent at higher temps.

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[Habbibie]

He doesn't say, but is concerned about his daughter driving over 100 miles. It's intermittent at higher temps.

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If its truly just random but only effected by higher temps then injection, electrical and the mechanical (NOT electrical) side of ignition is 100% out of the question (i.e. spark plugs & coils). main concern should be whatever it is that gets hot enough to fail is the number one suspect.... before on something like this I would use the expertise of Bob @Bedrck47 and @stamp11127 but Bob is gone and stamp is like a snowy day in Hawaii nowadays...

 

[stamp11127]

Bob and I had a little rivalry going on with who could answer the posts first. Every answer had to be 100% accurate or he would let me know about it. Since he has passed the desire is no longer there. May be time to sit in the shadows and let others have a go at it.

 

[1955moose]

He was a ball buster Bob was. He used to send me a pm whenever I screwed up. Always constructive though. Stamp no offense to the other top wrenches on our forum, but nobody comes forth like you do, with the knowledge for repairs. Especially in AC and electrical diagnosis. Nah, you gotta hang out, the partys just starting.

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[Jdcline54]

just to update, I went ahead and changed out all eight plugs and all eight cops over the weekend. all is well Expedition is running excellent, gas mileage has substantially gone up.

also I have to say this job isn't as painful as every post I've read makes it sound. They make it sound as if that number 4 plug (the back one on the right side) specifically is nearly impossible to get out. Although it was no picnic at the beach, I found it pretty easy with a 4 inch extension, a universal and a 10in extension. so for those people out there who have been avoiding doing this job for the fact that everything they read makes a sound so hard, I suggest just get in there and do it.
I had been putting this job off for over a year due to worries and concerns that I have read all over every page on the internet. And all I did was cause more damage to my plugs, and inevitably my engine.

thanks again to everybody that offered up some info for me. I just really like to understand what's going on before I jump into stuff.

 

[blue oval guy]

putting it off for 2 years?! The minute my old truck has anything wrong with it (engine related) i'm pulling it into my shop that same night. But that's just me..
good luck with your troubleshooting.

 

[1955moose]

Nothing in life is hard unless you don't understand, or haven't done it. I remember when I was I think around 11 or 12, and the pedal Crank on my sting ray bike broke. I was going to have a friend change it. I kept pumping him for info, on how he was going to do it, what kind of grease he was going to use. I said to myself, why pay this fool, I can do this job, and pocket the cash. I did it myself, and was so proud. Ridiculous easy, like most things in life. God I miss that sting ray bike, popped great wheelies!

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