ignition coil exploded

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74slnt6

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i was working on my car tonight after it was sitting all winter, and i put new plugs and wires on it. i was trying to start it but it wasnt getting spark. the coil was getting sort of hot, but i didnt think anything of it. and then it exploded all over my paint. what could have caused this? distributor wasnt getting spark, and the coil was obviously getting juice. anyone have any idea ? oh and by the way, i have no ballast resistor , its a 440 source distributor with the box built in. so i just want to get this all figured out.
 
What kind of coil? I assume you left the key in "run" for a period of time.

Some performance coils, like the big Accel coil and the big old rectangular Mallory coil, MUST be run with not only the stock type ballast, but a second one provided by Mallory/ Accel.
 
if its a factory style coil thats a big no-no also like above the accel yellow coils require 2 ballast resistors
 
Probably internal short in the coil, thus the no spark condition. Heat built up inside caused the oil in it to expand & boom!..
 
It is also possible that there is a short or fault in the distributor. Possibly the coil is being powered when the ignition is on the engine is stalled. The distributor powers the coil by pulling the coil (-) terminal to ground. It might be worth checking the lead out of the distributor to ground (distributor body). Place on low ohm setting and measure with leads both ways. If the reading is an ohm or less the electronic distributor is at fault. Using the multi-meter diode setting, may reveal open with leads one way and about 0.5V in the other, this is perhaps a good reading.
 
KitCarlson said:
It is also possible that there is a short or fault in the distributor. Possibly the coil is being powered when the ignition is on the engine is stalled. The distributor powers the coil by pulling the coil (-) terminal to ground. It might be worth checking the lead out of the distributor to ground (distributor body). Place on low ohm setting and measure with leads both ways. If the reading is an ohm or less the electronic distributor is at fault. Using the multi-meter diode setting, may reveal open with leads one way and about 0.5V in the other, this is perhaps a good reading.
Click to expand...

I'm not tryin' to be picky, this is a serious question. Do you KNOW this to be true, or just guessing?

For example, the factory Mopar ECU DOES DRAW POWER with key on/ engine off. My HEI does not. Pertronix DOES I have no idea about some others.

What this means is, MANY igntion systems are NOT SAFE to leave the key on/ engine off.

My cousin used to own a Jeep Wagoneer with Prestolite? igniton. He asked me one day "why have so many brain boxes burned up?" (He'd replaced 3 or 4) First I'd heard of it. I asked him "are the kids playing the radio with the key on?" Turns out HE did not know the DIFFERENCE between "run" and accessory!!!
 
I am trying to provide useful information. 74slnt6 in first post said it was a 440source distributor with built-in box. This suggests it is most likely a HEI type with a GM "type" module. Without reluctor pulses the dwell should timeout and not power the coil. The test I have suggested will test the output driver in the module. Most power semiconductors fail shorted. Any ignition designed to work without ballast, should power down.

They may likely have a diode, intrinsic or in the circuit with cathode at output anode to ground. In ohm setting diodes are not biased and should appear near open or 100K to megohms, in the diode check function the diode is observed. The diode is seen in mosfet, and IGBT, and Darlington transistor outputs. Viewing the diode and high resistance suggests the module output is most likely not shorted.

I do considerable work making custom uC based power electronics for engine controls for internal combustion, and diesel engines. It is a simple test for a faulted power components.
It is not fool proof since some parts fail with high voltage.

My fear is that if the distributor module is shorted, a new coil may also be damaged. Epoxy filled coils are not as tolerant as the old oil filled coils. This is a guess since we do not know coil type.
 
KitCarlson said:
I am trying to provide useful information. 74slnt6 in first post said it was a 440source distributor with built-in box. This suggests it is most likely a HEI type with a GM "type" module. Without reluctor pulses the dwell should timeout and not power the coil. The test I have suggested will test the output driver in the module. Most power semiconductors fail shorted. Any ignition designed to work without ballast, should power down.

They may likely have a diode, intrinsic or in the circuit with cathode at output anode to ground. In ohm setting diodes are not biased and should appear near open or 100K to megohms, in the diode check function the diode is observed. The diode is seen in mosfet, and IGBT, and Darlington transistor outputs.

I do considerable work making custom uC based power electronics for engine controls for internal combustion, and diesel engines. It is a simple test for a faulted power components.
It is not fool proof since some parts fail with high voltage.

My fear is that if the distributor module is shorted, a new coil may also be damaged.
Click to expand...

Thanks, exactly why I asked. Someone some time ago had an HEI conversion that was doing this.
 
Reverse wiring most often results in damaged electronics. Also open spark plug wire, or intermittent ground connection in module wiring lead to failure. It makes good sense to use a distributor ground wire since when timing is adjusted the clamp is loose to turn and so is electrical connection. Opening the ground when running kicks the module below the belt in a way it can't handle.
 
The problem is you had a constant 12 volts to the coil. Key on is to be 8 volts . Key cranking is to be 12 volts. when you were letting out of the crank position it was staying on 12 crank and fliping back to 12 run . you could have spiked it from a series of two overlapping 12's. The ignition if worked slow can sometimes operate two circuits at one time. You should always run a balast on oil filled coils to prevent this over heating from to much voltage. you probably had a jumper box or charger on it also. The oil shouldn't have damaged the paint unless it hit it hot. Properly wire a ballast for run only . It should be bypast for crank. Steve
 
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