Help with troubleshooting Truck just shuts off

[jusant]

Hello everyone, i'm having a hard time troubleshooting an issue with my truck. I think it's a fuel problem but I'm not entirely sure what's causing it. My truck is a 75 with carbureted 302 and mechanical fuel pump. After being on for 10 to 20 minutes it just shuts off. As long as I keep my foot on the gas pedal it tends to stay on. It will also restart, stay on for a couple of minutes and then shut off again.

Originally I noticed that the fuel filter would go dry. So I did a carb rebuild kit thinking something was clogged or a vacuum problem but didn't fix it. Then I put in a new fuel pump thinking that it went bad internally. Now I have fuel staying in the fuel filter but the truck still shuts off after about 10 to 20 minutes. Again, making me think something with the carb.

Is there anything else anyone could think that It could possibly be?

 

[Prizefighter]

Have you recently had exhaust work done? Your exhaust could be too close to your fuel line and causing vapor lock.

 

[Crush]

Try chanding the duraspark box. My 76 did the same thing. I completely redid the fuel system and ended up being the box. ��

 

[jusant]

No, I haven't had any exhaust work done. How do I check for vapor lock?

 

[jusant]

Crush, that was something we thought about, how do I check the ignition box

 

[DirtDonk]

You can usually verify an overheated control module by putting cool water on it to see if it works after. But since yours will start right back up after it dies, this test likely won't net you any usable results.

Have you checked all the fuel lines for age wear and/or leaks? Even a tiny bit of liquid at any part of a rubber or plastic hose will indicate deterioration that could be letting air into the fuel.

What about the in-tank fuel "sock" filter? It's very possible for it to be deteriorating and letting chunks of itself block fuel.

Do you have a tach? If the tach dies instantly when the engine does, you have an ignition problem. If the tach keeps going as you try to keep the engine going, it's fuel or something else.

Good luck.

Paul

 

[jusant]

Thanks Paul, I'll take a look at all of those things.

 

[Crush]

Jusant. Just go get one at advance they are only $15 or so and its good to have a spare. I didnt test for it just replaced it and it solved the problem. Make sure the plastic relief at the wires is the same color as the one that is on your bronco now. They are not interchangable

 

[blubuckaroo]

It's easy to test a fuel pump properly.
Just connect the suction side to your vacuum gauge and crank away.

 

[Broncobowsher]

Typical (but no guarantee) failures
fuel delivery: engine fades out. starts stumbling and gets worse and finally dies. takes a couple seconds to go from running fine to not running at all.
Ignition: sudden stop. Like the key was turned. How most coil/ignition module react when they get hot and fail.

A carbureted engine is very hard for the fuel delivery to go from fine to so out of whack it won't run instantly. The fuel bowl has to empty, or overflow, or whatever is wrong takes a moment to actually affect the whole engine and shut it down.

 

[jusant]

Thanks everyone for your input and help, turns out the floats where not moving in the bowl. Adjusted them and it appears all good. Ran the truck and took for a about 45min drive and it stays on and is running smooth!