hey everybody, i got a 1979 bronco with a 400M, mild cam, long tube headers, edelbrock 650(not like any of this matters). anyways, it has gone through two brainboxes. can anybody think of a reason or problem in the truck that could cause this, or just coincidence? any help would be appreciated.

 

Avoid using the cheap import control modules, they usually don't last very long. I believe they are still available in Motorcraft.
The different units are identified by the color of the plastic grommet that surrounds the wire bundle where it goes into the module. The most common color is blue.
Also, it wouldn't hurt to replace the pickup coil in the distributor too.
Heat and vibration are the two biggest enemies of these modules.

 

thanks, i'll keep an eye on that. anyone else, any input?

 

Check the voltage across the battery terminals while the engine is running; it should be around 14 volts. The reason to check this is because if you start going through ignition modules, one of the first things to look at is the voltage regulator. If it lets the alternator overcharge, onboard electronics like the ignition module (it's not really a "computer" per se) can fail.

Another idea: many times the ignition module is replaced because the pickup coil is actually failing. If the truck shuts off like the key was turned off, it's very common to suspect the ignition module and replace it. The truck starts back up after the swap, and the individual is left with the impression that replacing the ignition module solved the problem, when what really happened is the pickup coil simply cooled down enough to work again. The truck runs fine until it stalls a week later for what appears to be a faulty ignition module, when it's really the pickup coil failing. The process repeats.

For a quick check, you can check the resistance of the pickup coil by disconnecting the distributor connector, and checking the resistance between the ORANGE and PURPLE wires coming from the distributor. It should be 400 to 700 ohms. The resistance between either the ORANGE or PURPLE wire and BLACK should be open-circuit. However, since the pickup coil is an active circuit element, a simple resistance check doesn't really give you much detail, so a bad pickup can still ohm out fine. Also, they usually only fail when they're heated up and in use - not when you're checking it under the hood in your driveway.

And finally, of course, it is possible that you got 2 modules bad out of the box, but this is least likely. The most likely cause is that your pickup coil is actually what's causing your intermittent stalling issue, and the next most likely would be an overcharging issue. But my money is on the pickup coil. Best of luck.

 

thanks for the help, i'll give her a shot after work tomorrow