engine cut out/now runs fine???

Driving the 74 ranchero to a friends house get about 12 miles from home and engine cuts out. restarts with no issue but will not stay running for more than 30 seconds to one minute. have car flat bed home. cars starts at home but will not idle smooth and when RPMs are brought up it has a clear miss and is backfiring from exhaust and again will not stay running. Could not mess with it anymore had to continue with other business. now 4 days later check coil and its good check fuel level, good (holley with sight plug) have car running starts right up and runs fine in shop for over a half and hour. bring up rpms to 2500 and hold for over 5 min to get things hot. headers glow a little but car runs fine no cutting out. recheck fuel level and it's fine. thought maybe the spark box or the ignition pick up in the distributor. fuel leaning out??? But now it's running and can't find anything with it . Don't trust it now to go anywhere already have one $150 tow bill don't want to do that again. any thoughts? need the car for a project (my summer home project hauler) and can't trust it now.

 

Dura spark module

 

Fuel is fine fresh tank that was already used half way. spark box is a newer replacement ( year old maybe?) but I know that don't mean anything. will get another one.

 

Thanks for your suggestions. Sounds like Dan will be buying a spark box!

 

Ok replaced spark box and ran car and did some voltage checking. Car ran great for over an hour in barn vacuum steady and RPMs solid at 700. Coil voltage when running is 5.5 volts and not running with coil disconnected is 7.5. starting voltage is a full 12 volts. I have never paid much attention to this until now but both the coil and the spark box get pretty hot. I would call the box very warm and the coil to hot to touch. The top of the engine didn't even get that hot and I had the hood open the whole time and it was pretty cool under the hood. Should I be concerned? Just for laughs I checked one of the other cars and the coil voltage was a bit higher. I had 6.5 at the coil when running and 10 volts disconnected and full 12 at start up and while running and nothing ever got too hot to touch. need this car to reliable using for a project and don't want a repeat of a week ago (flatbed home) Thoughts please. Thanks Dan

 

Ok replaced coil with known good unit. But first I ran both the t bird and the 79 ranchero for one half hr then checked coils. all three cars have the same dura spark system. the 79 was warm the t bird was warm the 74 ranchero would make my skin Sissle when I touched it way too hot! yet all three cars have 6 v at coil when running. all three cars run good and show no signs of any issues. but the 74 rancheros coil gets so hot and I just can't pinpoint it. If I decide to drive it this way I know I am asking for another flatbed ride home. Still need your thoughts on this one has me slightly puzzled. could the pick up in the dizzy cause something like this? how would I check that one with a meter?

 

I was just asking about the pickup. I was thinking the same. I will check grounds but everything else has proper voltage.

 

Thanks I will check that all out. took it out today and it runs great. just that damn coil get so smokin hot!!!