1973 Dodge 318 Ignition problems

[ConfusedbyMopar]

Truck is having ignition issues.  No spark sometimes...other times it fires right up.  I replaced Ignition coil and condenser but no change.  thinking ballast but not sure if they act that way.

[Bloo]

Should have electronic ignition in 1973. Condenser? What condenser? The radio interference one?

 

Ballast can act that way. That or the ignition module, or the pickup coil in the distributor. Pull the plug off of the ignition module. How many pins? 4 or 5? If 5 I would probably replace it with a 4 pin.

 

Should have a 2 section ballast in 73. If it has a 4-pin ignition module (instead of the 5 pin it would have had when new), the second half of the ballast is no longer used. The second half was almost always what failed on ballasts.

 

You could take the ballast off and look a the back side. Some really old ballasts were not potted (you can see the coils of resistance wire) and the resistor can sort of move out of the back with heat and short to ground. I am pretty sure they fixed that by potting all of them long before 73, but I might take it off and look just in case.

 

If it's got a 4 pin module, and you still have voltage at the (+) terminal of the ignition coil when there is no spark, the ballast isn't the problem.

 

Most likely failure is the ignition module. The pickup coil in the distributor could also be bad.

 

 

Edited November 7, 2020 by Bloo (see edit history)

[61polara]

Check the wire from the coil to the distributor for internal breaks.

[John348]

As I recall the modules were always a problem

[Tom Boehm]

I'd be interested in hearing more about the ignition module and its problems. I have a 1973  318 with similar symptoms. Also where can I get a reliable quality new ignition module?

[JACK M]

3 hours ago, Tom Boehm said:

I'd be interested in hearing more about the ignition module and its problems. I have a 1973  318 with similar symptoms. Also where can I get a reliable quality new ignition module?

 

Unless you get lucky you will probably have to go aftermarket.

You might try Mopar Performance, I haven't looked thru one of their catalogues in awhile.

The distributors will fail on occasion as well.

 

In my race box I carry an old rusty OEM module. I lost spark on one of my cars and subbed in that old chrome box that had not been used for many years.

The car started and ran well so I bought a new module at Autozone only to find that the engine would not run. Returned it and bought one from NAPA, also didn't run.

Bought a distributor thru Mancini Racing and the old module that I originally suspected would run the car.

I suspect there is a huge difference between OEM and aftermarket modules. But the local Chrysler dealer kid never even heard of one, and his books didn't go back that far. 

 

[Bloo]

It isn't a really a problematic part. There were some issues for the first year or two (when GM and Ford were still using points on almost everything) and nobody knew how to troubleshoot it yet.

 

In 73, as originally built, there was a double ballast resistor. One half of it was the same 0.5 ohm resistor used with points, the other was a 5 ohm ballast for the power switching transistor in the module. In 73, there were a bunch of failures of the 5 ohm half. Better ballast resistors followed, and then some time later a module redesign that eliminated the 5 ohm part of the ballast resistor.

 

A ballast resistor is an easy fix, but at the time, few people knew so the tow truck was called....

 

Confusingly, if you replace the module today on a car with the 5 ohm ballast half burned out, the car will run. The owner will probably think the module was bad. Why? Because new Chrysler ignition modules (for decades now) have only 4 pins in the connector. The missing pin went to the 5 ohm resistor.

 

Any factory installed original electronic ignition module (in any make of car) that was made in the mid 70s is on borrowed time after 80K miles IMHO.

 

I have driven hundreds of thousands of miles on Chrysler systems like this, and have never had a module failure. If you have the newer 4-pin module, you don't have much to worry about. Mopar Performance's "Orange Box" is the best one ever for a street driven car, but it is out of production (watch for it at swap meets). If you are worried, toss a spare module in the glovebox.

 

 

Edited November 8, 2020 by Bloo (see edit history)