Hey all, I'm new here and recently received a 1973 D100 pickup from my dad. All was going well until last week the truck started having a misfire. At first I thought it was the ballast resistor but after a swap it still continued to misfire.

So after replacing the voltage regulator, ignition control module, cap, rotor, ballast resistor, spark plugs, and making sure all grounds were clean I'm still having trouble. The only thing I haven't replaced is the alternator and the plug wires.

There seems to be a pattern. I can start the truck and it runs smooth at idle and well through the RPM's. Then after 5-10 mins of running the truck will start to misfire after I rev it out. If I come back to it the next day and start it up it will do the same thing. Another thing I noticed is the battery is charging at 15.5 volts

The truck is all stock except it has an Edelbrock intake, a Carter AFB competition series carb, and LED dash lights. Any help would be greatly appreciated.

 

Change the plug wires....
Make sure all the grounds are good... Add a ground wire from the reg. Mounting bolt to the Engine. and see if that helps... Also make sure the battery is charged.

 

I recently had a similar problem with my 1990 D-150. It turned out to be bad plug wires (3 of them) were breaking down some where in the wire when it warmed up.

 

I'll run out and get some plug wires today and report back. I just installed a negative battery cable with a ground wire that runs to one of the radiator mounting bolts as well as to the drivers side head. I also put a ground strap from the regulator to the back of the passenger head.

 

Head or block to frame, frame to body!

 

If you have a multi-meter there are some you-tube video's out there that are pritty good. I was convinced that the spark plug wires were not the problem with mine, because they were less than a year old. But I was wrong when I ohm tested them.