Igntion problem?
 

I just bought a 84 bronco with 351w engine.The guy I got it from said it starts and runs for 30 mins. then just dies and if you let it sit for an hour or so it will start again and run for short period of time.He said he replaced the dist.,plugs,wires,cap,rotor and igntion module with no luck.If anyone has suggestions on what the problem might be that info. would be greatly appreciated.

It could be quite a few things but heres one possibility...Maybe the fuel pump heats up after 30 minutes to a point it stops working and then it must cool down for that hour or so you describe before it runs again. Do you hear the fuel pump priming sound after the truck dies and you try to start it?

Make certain the replacement ignition module was indeed the correct one for that truck/engine combo. If you are uncertain, put a hand on the module after its been running for about ten minutes. If its the wrong one, it'll be pretty warm and its shutting down from overtemp'ing. 84 should still be a Duraspark if I recall correctly. those modules are also notorious for just up and quitting for the heck of it.

I had a similar problem years ago on a 302, turned out to be a bad coil.

It also has a new coil.I wonder if it could be a bad ground because the body is pretty rough.I was planing on taking the body off along with all wiring then wire the ignition directly threw a toggle switch to try to get it to run.

If the length of time it runs before just up and quitting is fairly consistant, its more likely a heat-related issue than anything.

Greystreak - my '84 came with a EC-iv ignition, the module is on the distributor, but there was an option for the duraspark ignition on both the '84 and '85 models.

This issue though sounds more like a fuel vapor locking issue to me, not ignition. What type of fuel line is running to the carb?