Hey all, great forum. I need some help figuring out whats going on with the ignition system on an '85 f-250 7.5L.
Truck is/has been running poorly (sputter, no idle, black smoke out the exaust) and I've just only began trying to diagnose the cause. Pulled plugs today and found they were all blackened up. Replaced plugs and cleaned up the dizzy cap and rotor and fired it up...ran a little better with less black smoke out of the exhaust but still had trouble idling complimented with the occasional sputter.

So I started talking to the primary owner of the truck (my dad) and was informed he replaced the ICM a few years back from a donor truck he had on hand. He can't remember if/how he verified the ICM's interchanged so this makes me a little concerned the trucks original ICM has been replaced with the wrong one and somehow managed to still run this whole time albeit poorly imo.

I haven't been too successful trying to rule out the ICM as the culprit by checking part#'s online so I'd like to post them here and see if anyone might be able to tell me whether or not the part number and corresponding ICM is the correct one for this truck.
The numbers I pulled off the box installed on the DS inner fender are as follows:

Motorcraft-Duraspark 12A199 A2C.

The old box has since been tossed out so I don't even have that for a reference.

Also, even if this ICM turns out to be the right one for this truck, is there a way to test them to see if they are good or bad? Just for fun I probed the the 3 wires leading to the dizzy and was getting weird readings on 2 of the three wires. With the ignition switch turned to "on", I getting a fluctuation of 2 to 8 volts pretty consistently. That doesn't seem right to me but I'm not familiar with these ignition systems so .

Any input would be appreciated...
THANKS!

 

Your 460 truck uses the DuraSpark II ignition system.
Any module with blue plastic where the wires enter is correct for your truck (though some brands are better than others)

Your blubbering and rich running truck sounds like the carburetor power valve is leaking.
Whether due to age or an errant backfire, I can't know.
Is the exhaust eye wateringly rich?
Does the truck run better at high rpm's and 'pop' on deceleration?

Usually when the module goes, it fails when hot and will restart when it cools off.
Or it fails completely with a backfire, and is dead on the road.

From my personal experience it sounds like too much fuel and not an ignition issue.

 

Probing the three wires from the distributor you will find that black is the only ground for the entire ignition system and if you read resistance across the orange and purple wires of the ignition pickup you should find between 450 and 950 ohms.
Under 400 or over 1000 you should replace the pickup, or the entire distributor.

Fluctuating voltage makes sense.
This coil has a resistance wire in the 'run' circuit.
8 volts or so is max, and when the coil reaches saturation current flow stops and energy creates heat.
It's not such a good idea to leave the ignition on with the engine off.

 

This might explain why I was having trouble matching things up.

I'll have to check the for the "wateringly rich sympton" but truck does run much better at high rpms and iirc has made a popping noise when decelerating. I keep you posted on what I find and thanks for your help.