Spark issue

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R72Demon

R72Demon

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On my 72 demon with stock mopar ignition system with orange box. I ran the car up to operating temperature and while idling I smelled something odd from under the hood (can't really describe the smell but it wasn't like anything I've ever smelled before) so I shut the car down. After looking under the hood, the only thing I noticed was the ballast resistor was really hot. I tried to start the car back up, but it wouldn't fire. So I pulled the #1 plug out to check for spark and there was 1 initial spark and then nothing at all. So I got my test light out and started checking the ballast, coil, etc. About 5 minutes went by and I hit the key and the car fires right up. I pulled the #1 plug out again and I'm getting constant spark but it's a yellow-ish white color instead of blue.
 
Check the back of your ignition module and see if you think it might have been the smell.
I have seen them just melt the epoxy out and run down the inner fender some were so bad before they died.
 
I will pull it off tomorrow and check it. The 1st orange box I put on the car was junk right out of the box.
 
TrailBeast said:
Check the back of your ignition module and see if you think it might have been the smell.
I have seen them just melt the epoxy out and run down the inner fender some were so bad before they died.
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This one did just that, left a mess down the firewall. Still worked when I replaced it, though.

  • ignmodulemelt.jpg
 
I pulled the ECU off and didn't find anything melted. I replaced it with another one anyways and I still have them same problem of loosing spark when it gets hot. I also discovered that when it looses spark if I crank the engine over a few times and stop cranking, then turn the key back to the "ON" position it gains spark back and fires once.
 
If you have a second distributor, install it.

I once had a similar issue, cutting out when hot. The pick-up coil of the electronic dizzy was going open circuit when the car warmed up.
 
Check the reluctor gap in the distributor. .008" with brass feeler gauge...

If too wide, it can start cold, then not when hot... Been there done that....
 
You are experiencing the one-spark test. This is normal. It says the following items are working; the ballasts, the ECU and it's ground, the coil,and most of the wiring. The only things not proved by this test is the magnetic pick-up, it's wiring and the reluctor gap. The start circuit is also not proved.But if it cranks, it is insinuated to be working.
To test the trigger, the first part was mentioned, to check the reluctor gap. The trigger can be ohmed out, but you need to prove the trigger wires are not fatigued inside their plastic sheathing. I don't recall the spec, but I could estimate it to be around 400 ohms. After that you can ohm out the wires between the trigger and the ECU. These should be close to Zero resistance. The trigger can also tested by triggering it with any iron object, like a screwdriver; just pass it over the sandwich mimicking the reluctor vane.This should send a spark from the removed and near-grounded coil-wire, with every pass,slap or tickle.Since the output from the trigger is so small, any little resistance in the wiring can kill it, so no splicing other than soldered.And you see that little factory plug? Check the pins
Ballast resistors work by heating up.They get hot soon after the run circuit is energized.Every new one I have ever installed stank on the first cycle or two.
 
MrJLR said:
I'm thinking coil.....

Jeff
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I tend to agree. Some of you guys on here know I do not like guessing "throwing parts and money" at a problem. But sometimes you must. This is likely a box going bad or a coil going bad. It's nearly a tossup. Pick the one you can buy or get or borrow "'cheapest" and replace it.

If you are not set on absolute "resto correct" this might be a good time to consider an HEI module conversion. A couple of members on here even managed to mount an HEI module into a scrapped Mopar ECU

Here's one now

HEI in Mopar ECU casing

Anyone ever try rebuilding an ignition module?
 
Changed both the coil and ECU. I started the car up and left it running, ran for about 5 min. then it died and had no spark. Guess I will check out the distributor now.
 
R72Demon said:
Changed both the coil and ECU. I started the car up and left it running, ran for about 5 min. then it died and had no spark. Guess I will check out the distributor now.
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Have you checked the reluctor gap in the distributor yet??? .008" with brass feeler gauge....
 
well that pretty much proves a bad magnetic pick-up,then.
But not totally.
When it dies;touch nothing! Do not even touch the ignition switch!NO-thing!
Check for battery voltage into the ballast, and for the driver voltages out of the ballast and for voltage at the coil.
Until these are proven correct you don't want to throw more parts at it. But if the voltages are correct, or nearly so, then I would swap in a different or new pick-up.
 
R72Demon said:
Changed both the coil and ECU. I started the car up and left it running, ran for about 5 min. then it died and had no spark. Guess I will check out the distributor now.
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I would suggest you learn to troubleshoot instead of throwing parts at it. EG let's say a loose connection in the bulkhead connector, which a member on here recently experienced. You could swap parts until you are broke and not fix it

For starters, jumper the coil + to a battery source with a clip lead and see if it starts / runs.

Pull the distributor connector apart, and take up the engine harness half. With the ignition powered, bump the bare end of the connector to ground and see if it makes a spark each time you do so.

Make ABSOLUTELY certain the ECU is grounded.

"Work" the connectors.....the ballast....the ECU and most especially the dist connector in/ out several times to scrub the terminals and feel for tightness.

With the key in "run" measure coil + and neg coil voltage. Coil + should be "down" from battery somewhere around 6-10V. Coil neg should be very low, around 1 volt.

If coil + is much lower it's not getting good power. If coil + is way high, up around battery, the coil NEG is too, probably. THIS SHOWS an ungrounded ECU or bad ECU, or bad connection

Inspect the dist internally. Look for strike damage at the reluctor, rust, debri. Put your meter in the dist. connector on low AC volts and crank the engine. Dist should generate about 1V AC

Find the high side of the ballast. It should be close to battery. "Wiggle test" the connectors and bulkhead connector while checking
 
Last edited:
67Dart273 said:
I would suggest you learn to troubleshoot instead of throwing parts at it. EG let's say a loose connection in the bulkhead connector, which a member on here recently experienced. You could swap parts until you are broke and not fix it

For starters, jumper the coil + to a battery source with a clip lead and see if it starts / runs.

Pull the distributor connector apart, and take up the engine harness half. With the ignition powered, bump the bare end of the connector to ground and see if it makes a spark each time you do so.

Make ABSOLUTELY certain the ECU is grounded.

"Work" the connectors.....the ballast....the ECU and most especially the dist connector in/ out several times to scrub the terminals and feel for tightness.

With the key in "run" measure coil + and neg coil voltage. Coil + should be "down" from battery somewhere around 6-10V. Coil neg should be very low, around 1 volt.

If coil + is much lower it's not getting good power. If coil + is way high, up around battery, the coil NEG is too, probably. THIS SHOWS an ungrounded ECU or bad ECU, or bad connection

Inspect the dist internally. Look for strike damage at the reluctor, rust, debri. Put your meter in the dist. connector on low AC volts and crank the engine. Dist should generate about 1V AC

Find the high side of the ballast. It should be close to battery. "Wiggle test" the connectors and bulkhead connector while checking
Click to expand...

The only reason I thru parts at it was because I already had known good parts from another car.
 
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