Plug wire fire

[Steve Meltzer]

Or at least I think so. I drove my GTC on Sunday and got stuck in TERRIBLE traffic. I'm not if sure the car over heated (T max was about 105C, I think), but I finally was able to pull off the road and let the car cool some. Eventually get home at a reasonable temperature . Drove the car Monday and Tuesday and it ran great, both days, no overheating. In fact, it ran excellent...best ever in years! (Finally got the carbs redone by Pierce and synched, tho' mix not fine tuned, just at his approximation.) Opened the hood last nite and ...

On the left, plugs #11 and 12 have this white, ash looking stuff, which I was concerned might be coolant, tho' this finding was not present prior to last nite. Picture enclosed.

However, on further review, with the car cooled off, I think this was an electrical mishap....the coolant level in the overflow tank was about 1/2, as it should be, indicating that none of it spewed nor combusted. The residue is powdery, not wet or greasy. The plugs are sl. sooty, probably a bit rich, but not too bad for a Ferrari . No white residue on the plugs, but wires and end caps are beyond toast. I don't think they'd look like this, even if bathed in hot coolant from a blow head gasket. I think they got fried of their own volition. Finally, none of this was present until 48 hours, and 4 other driving episodes, after the freeway traffic fiasco.
Betting this is related to a grommet failure (or, more honestly, my failure) allowing the plug wire(s) to be damaged by the sharp edges of the plug wire tube orifices. Pictures included. Could be worse. s

[tim]

Greetings… Are you running the standard ignition or something with an amplifier. I've seen a lot of shorted wires and boots but not with that kind of damage. This is what happens when your car is "running better than it has in a long time". See previous pics of my valve seats. I think the residue might be from burnt paint.

Tim

[Steve Meltzer]

Stock ignition...points, no boxes. Dyke thought this could be an exhaust leak, but it will be a few days until I can get to it to look.
Now not so sure my theory about electrical arcing holds water. Not solved, yet. s

[tim]

Greetings… I think Dyke has hit it. I can't imagine any ignition system being capable of that kind of damage. Start her up and give it a listen,

Tim

[Steve Meltzer]

when i get home, i'll have to replace the plugs and wires and then check it out. won't be able to tell a thing as it is now, that's for sure.
But, before I do that, let me see if there's an obvious leak in one of the header pipes. i didn't hear any increase in exhaust noise. if this was someone else's car, i'd say it was "very interesting"! s

[John Vardanian]

To me it looks like the aftermath of plasma.

john

[250GT]

Steve,
you're white snow is owing out of the wiring
this "coating" protects the carbon core inside
the melting(probably exhaust ) must have come from out side.
Well after 60K km its not a luxury to replace ALL of them

C.

more info here:

.
Probably the most efficient transfer of spark energy is made with solid core spark plug wire. This type of wire was extensively used prior to the 60's before the introduction of car radios as standard equipment. A few modern day exceptions exist such as certain race applications and a few European car manufacturers. The problem with solid core wire is that it emits large amounts of RFI ( radio frequency interference) which affects radios, and onboard electronic systems in cars. When current passes through a wire, a magnetic field is formed. If the current flow is switched on and off rapidly as with an ignition system, RFI is caused by the magnetic field collapse (some refer to it as EMF which stands for electromotive force). When manufacturers started installing radios in cars, a solution was needed to reduce the RFI. One of the first solutions was to mount resistors on the wire ends to reduce the current flow and consequently reduce the EMF and resultant RFI. The second solution, and the most popular by far, was to make the whole wire a resistor. Thus the age of carbon core wire (sometimes referred to as graphite core) was born. This type of wire needed a whole new type of construction over conventional solid core wire. Carbon core wire's basic construction starts with a non conductive structural member (nylon or Kevlar™) over which carbon fibers are deposited. These carbon fibers are typically blended with latex or silicone to form a flexible coating. A layer of EPDM rubber is then deposited over the core as primary insulation. Next a nylon bonding weave is placed over the wire which is followed by a final coating of either EPDM or silicone rubber. When new, this wire performs as designed. Over time however, with heat and vibration the carbon fibers tend to loosen which degrades conduction and eventually requires replacement. For this reason some OEMs (original equipment manufacturers) recommend replacement every 3 years or 60,000 KM. Carbon core wire is quite economical for manufacturers to use while suppressing sufficient RFI. This wire typically has a resistance of 3,000 to 20,000 ohms /ft. depending on the manufacturer.

[Steve Meltzer]

I don't, and never did, think that the wires were inherently defective, but if they're the culprit, it's because of a defect caused by their contact with the wire "loom tube". The wires are only about 2 years old, so, when they get the "boot" (ha! ha!) it'll only be the two of them. s

[330Jim]

I think you have a mixture issue on that barrel of the carb causing those two cylinders to run very hot. Look at the paint on the exhaust shield, it is burnt. I suspect your exhaust was glowing red hot and it burned your ignition wires. Note the plug ends show the most damage adjacent to where the exhaust pipes would be. If I am right,once you adjust the mixture and replace the plug wires, it should run even better.

Cheers Jim

[Steve Meltzer]

thanx to all of you for your thoughts on this. lots to think about and check out. i'll post more later. thanx again. s

[Steve Meltzer]

The Denouement:

In the practice of medicine we have long adopted the model of the “clinicopathological conference” (CPC) for the discussion and teaching of atypical presentations, weird diseases and rare afflictions. As every medical student knows, the most famous of these “CPCs” come from Harvard and are published in the highly-vaunted New England Journal of Medicine. Knowledgeable experts and highly respected physicians are asked to weigh in on the available data before the final diagnosis is given. My smoldering, melted ignition wires and adjacent heat shield seemed to make that analogy apropos....

With the burned wires temporarily replaced, the car fired up pretty well and you could see that carburetor #1 was getting no fuel. That turned out to be due to a piece of dirt in the needle and seat and I could also see the “eccentric” clamp on #1 carburetor vibrating, as it was loose. With those two seemingly minor issues resolved I took the car out and it ran great, with no burned wires upon my return home.

In retrospect, when I was about 4 miles or so from home, I did think that the car had lost some power and that it did idle, at the lights, about 200 RPMs slower. I guess I’m not sophisticated enough to tell that the car was running two cylinders from spec, especially since it’s not run quite right for some time.

In short (pun intended), I think the debris in the needle/seat on #1 led to a lean condition already present in #11 and #12 vis a vis a non-functioning (loose) eccentric clamp, which led to excessive heat in those chambers. The wires melted from the hot exhaust pipes. Looks like there might have been some electrical arcing across that acorn nut as well, once the insulation melted into that white mess.

I’m also surmising that I might have been lucky to get home and stop driving before a similar mishap occurred on the other side.

Comments? Did I interpret this correctly? 330 Jim nailed this one on the head.

Thanx again to all of you for your support and ideas. s

[330Jim]

Great news, I am glad you got it back on the road. Your findings and observations match what I would expect to see.

Cheers Jim

[Steve Meltzer]

Thought I'd post some pictures from the "other side" of the heat shield. You can see the change in the heat insulation material I put there to help save the "crinkle finish". (Not very helpful, even under normal circumstances.) Also the change in the finish on exhaust pipe #12. Thanx again for everyone's thoughts and input. s

[John Vardanian]

Steve, glad you found your problem.

This is a pretty serious thing, the melted things are not that big a thing compared to internal damage (burnt piston, etc.) that this might have caused.

So, what is the lesson learned here? How can one prevent this clogging of jets from happening? Thanks.

john

[Steve Meltzer]

On my Daytona coupe, I have one of those fuselage-shaped in-line filters just before the fuel log and I may put one in the GTC as well.
With the hard yellow fuel lines of the GTC, it won't be as seamless as putting it in the braided Aeroquip line, where I was able to neatly tuck it up under the cowl.

The GTC ran strong and sounded good with the temporary wires, but I might compression test at least those two cylinders to be sure. Much easier with the heat shields in the "paint shop". Pretty darned hot in there.

s