roasting coil wire

has something really weird happen tonightin the powerwagon. the coil wire right at the cap flat cooked itself in half. no misfire, no hard starts, hesitations, nothing leading up to this point. i was right in the middle of the busiest intersection in town and i hear this loud POP! then im dead in the water. upon inspection the coil wire failed right at the male end in the cap, the brass end looked perfect, not burned, nothing. got the truck home, pulled off the cap, rotor, wires, everything, and checked for carbon tracking and holes, rub marks, anything, and found nothing. put it all back together and i have a horrible hesitation off idle, sometimes, not all the time, and i noticed my tachometer pukes out when it has this hesitation. with no consistency it makes the tell tale pop pop sound like a wires arching out upon cranking to start, but only sometimes, and when it does it, i dont see any lightning shows from the cap or wires.

with that being said, i have a new cap and rotor with brass tower inserts, a month old, wires are 2 years old and have 12,000 miles on them, solid graphite core accel super stock 8mm's, champion platinum plugs, and a digital MSD 6a thats 9 months old pushing a blaster SS coil, Any ideas as to what could have caused the coil wire to burn in half? faulty wires? do graphite core wires fail in this manner when subjected to capacitive discharge ignitions? and why would the tachometer drop to zero coinciding with a huge misfire when it stumbles on off idle acceleration?

It's possible you may have hurt something in the MSD. I don't use MSD, so don't know much about what -- all sorts of wires are acceptable. You probably burned the wire out from the inside, which caused it to open, and that generates a huge high voltage just like lightning. That is, the ignition system, in normal operation, loads down the voltage because of the combustion process. If you have an "open" connection, this allows the high voltage to climb out of sight, and it can reflect back into the electronics and cause damage or failure.

I just saw a post the other day with some one having trouble with a MSD unit. One of the comments was that MSD does not recommend solid core wires. May be an issue or not. Just thought I'd put it out there for you.

Try measuring the resistance of the ignition cables. I do with an Ohm meter from cap terminals to plug center electrode. That will test for any open, 10K ohms or less is good for me. Also measure coil to cap cable, I assume you changed that.

An open in a wire, creates a hot spot due to spark jumping, as it burns creating a larger gap and goes till it cannot jump further.

Back in the 1972 I designed an built my first cdi ignition, it was a bit hot, and burned up a set of ignition wires. The Ohms of each was greater than 1 megohm.

On MSD ignitions, the primary coil voltage is very high and is not compatible with most tachometers. The tach should be connected to a tach output wire, not the primary coil wire, and if it's not, it might be the cause of your issues.



http://www.msdignition.com/Products/Ignitions/Daily_Driver/6201_-_Digital_6A_Ignition_Control.aspx

thanks guys! i think i figured out most of the problem, i still need to measure the resistance through the wires, but i have a bad feeling my blaster SS was on its way out for a while now. fired it off this morning when it was cold, and i could hear the arching much more, everytime id blip the throttle it would do it. I have a hunch this is how it played out, the coil was failing in its di-electric properties, stressed the coil wire, coil wire turned to powder, blew itself apart, and the coil had nowhere to dump its energy, so it blew the side out. I could see the coil sparking nice and blue straight into the firewall, and i could see that messing with my tach, since my old autometer units (i have 2) seem to be extremely sensitive to electrical faults. My crimp on the faulty coil wire wasnt as sufficient as id like it to be i noticed, it wasnt fully seated in the tower, so i made sure my new wire would fully seat on the tower, i dont get though that it took 2 years for this to happen, and the tower in the cap wasnt damaged at all. reguardless it couldnt have been helping the situation. I was reading MSD tech sheets all last night and they recommend using a spiral core wire, im not, im just using straight graphite. however i have been for 7+ years on 3 diferent rigs and this is the first problem ive ever had. fired up the truck after replacing the coil and its just like it always used to be, the only difference i noticed was the exhaust isnt nearly as "raunchy" as it was last night, makes sense, faulty ignition coil, unburned fuel and so on...so time to ohm out the wires!!! then possibly build myself a set of spiral core units. thanks again guys!

I would change the wires before I changed the coil. Anytime you get a broken plug/ bad wire as I said before, this leaves "no place" for the spark energy to go, and it will arc to the shortest place it can find. The higher the energy/ voltage system you have, the worse this gets.

Right on the money.

67Dart273 said:

It's possible you may have hurt something in the MSD. I don't use MSD, so don't know much about what -- all sorts of wires are acceptable. You probably burned the wire out from the inside, which caused it to open, and that generates a huge high voltage just like lightning. That is, the ignition system, in normal operation, loads down the voltage because of the combustion process. If you have an "open" connection, this allows the high voltage to climb out of sight, and it can reflect back into the electronics and cause damage or failure.

Click to expand...

makes perfect sense. sounds like i need the proper wires reguardless. accel 5040B's any good? Or should i shoot for the razoo 480 ohm per foot MSD units?