I have a 79 Bronco. It starts right up in the mornings. But when it gets warm, if it dies, or you turn the key off, it won't start. Engine turns but no spark. I've changed all the electrical components, even the starter switch. Hope you guys can help. Thanks.

 

Have you checked the fuel pump, I have a 78 and unless you have added an aftermarket one, i think they are on the block so i can see them getting pretty hot. I don't know how you would check this but it would be something to look into. Also take a look into your col wires and see if you are getting any voltage to the coil. You may have a short somewhere.

 

Fuels not a problem. It's just not getting a spark to the plugs. Thanks.

 

And the coil wires? I know when i bought my 78 the PO had cut into the wires and when he attempted to splice them together he did a bad job so every time they moved they lost connection

 

Nope new coil, and wires tight. Thanks.

 

My Dad had an '82 Ford station wagon that did the same thing. Found out there was a electronic brain on the fender well. About 6-8" square and 1.5" deep. When the car died, we poured a cool drink over the box......magic......the car started right up. Read up on them and found out the potting material inside broke down and heat created issues. Once cooled, all was good for a while.

We actually stumbled onto the fix when a drink got spilled on it trying to fix it...lol

 

Oh ya i know what your talking about, i replaced both the ignition box and the little brain box (forgot what it is) i don't know if he has the same issue or not

 

Ah yes. The MCU (Microprocessor Control Unit). Had a big plug in the center of it. It was the first generation processor, before the EEC-series. Never had trouble with my MCU. And I never drank while under the hood

A problem I DID have, which could be relevant to the problem at hand, is a heat-dependent intermittent-open in the distributor's pick-up coil. Would start fine when cold, would run fine. But shut it off after underhood temp was up, and no start due to no spark. When it all cooled down enough, it made contact, and would start.

A way to test it: with engine cold, unplug the connector to the distributor, and with a DVM on ohms, find the pickup coil. Mine was around 1000-1200 ohms I think, but I'm doing this from long time ago memory. Anyway, find continuity of the pickup coil, and measure the resistance. Then when it is well-warmed up and won't start, open the hood and get that connector apart and measure it again quick before it cools off. If it now reads way way higher resistance than before, replace the pickup.

I verified mine was bad by pulling it, put it into two baggies for waterproofing, and submerged it into a pot of water on the stove. Brought up temp while monitoring temperature and resistance of the coil. As the water started getting real warm - bink! the resistance went to infinity (open circuit). Pulled it out of the water, when it cooled some, it reconnected.

Easy to test it under the hood with a DVM, try it. May or may not be the problem, but the cost to test it is 0$

Also, if you switch the DVM over to AC Volts on a low range, and have someone crank the starter, a working pickup with the reluctor spinning by it will generate an AC voltage. An open pickup will generate just a tiny signal, too small at cranking speeds for the ignition control module to read and use.

 

Thanks GruesomeJeans that's one of the first things I replaced. Thank you too Torky2 but I think when my friend checked it, it wasn't getting power to the distributer. But I'll double check. This is really a great place to get info.

 

Your very welcome.