Hi all - I have a 76 390 1/2ton that I just acquired. I had a fixer once before when I was 15, but I just replaced parts that my dad told me. I am very capable, but don't know enough to accurately trouble shoot my problem. Here it is.


When I first got the truck running (pulled out all sorts of extra wiring done by previous owner, fixing shorts....) it ran fine. I started driving it around the property and loved it. About a month went by with no driving. I went out and it started right up. I drove it almost a mile and it died while driving. It took about 3 minutes or so of cranking (not steadily) to get it to stay running. Then, about another mile it repeats. When I try to start it after a stall, it sounds like it wants to run a little, but dies as soon as I let go of the key. If I hold the key while it is sputtering, it will start up sooner, but takes a good deal of time consistently holding the key. I got it home, and it will idle for a few minutes before it dies. Same trouble starting. If I let it sit, I can go out and start it right up first time. It will run for a few minutes, maybe ten, then it dies and repeats the trouble.

What I need help with is two fold.

First... I would love to get ideas about this problem. What have others experienced...

Second... How do I trouble shoot this? Is it electrical or fuel or vacuum? How do I determine if the carb, or some part of the carb is working right? Can it do this kind of thing? How do I determine if the coil or ignition mod is overheating or shorting? Can that cause a problem like this? I know there are vacuum lines all around. Can they cause this? Any general information about these systems that would help me daignose this and other future problems would be greatly appreciated.

Anybody got any input? Any other information that I need to share?

Thanks
Adam

 

I would suspect one of two things. Dirty fuel filter or a heat related ignition problem. change all the fuel filters for the first. Carb, fuel pump and accessory one if there is one. The ignition would be either the box, then sensor or the coil. The way to check is see what kind of spark you have cold then way kind of spark you have right after the problem happens. If it is weak and not a strong blue spark, change the coil. If not that change the ignition box and then sensor. It is best to do the last two as a pair as if you guess wrong it is possible to screw up you new part.

 

As you described it as a fixer, was the truck parked for quite a while before you got it, and "got it running"? If so, the fresh gas is probably dislodging a lot of old crap in the tank/ fuel system. I'd try cleaning/ replacing any filters in the system, maybe add another filter, anything to catch the crap before it gets to the pump & carb. Too late to drain any old gas out, as you've already run it quite a bit. Might have to clean it out a few times before all the gunk is gone. I'm going through the same thing with a '71 Mach1 I picked up, been sitting in a garage on jack stands for 23 years- I'm on my fourth inline filter, 3rd can of Seafoam, and heading out to clean out the 780 Holley on the 351C-4V, for hopefully the last time- starting to run reeeel good