I have a 75' F-350 with the 390. It recently started having an issue. When it idles for a while (~20 minutes) It will die like it does when it runs out of fuel even though it isn't and won't restart. Then maybe 20 minutes later it will restart. Then idle just a bit longer and it dies again. The next day I started it up and drove for probably 20 miles and home with no issues, no extended idling.

Then about a week later(yesterday) I drove about 40 miles to get lumber to put some new bedsides on it and on the way back I stopped at a store close to home. My dad ran in to get some things and I stayed in the parking lot. I left it idling as i was checking all the lights on it. After about 10 minutes it started sputtering as I was checking the brake lights. We ended up sitting in the parking lot for about 15 minutes unable to get it to start. I then pulled the hose off of the carb and bled the fuel line. It took about 5 seconds of cranking for fuel to spit out. Then I put the line back on and started it up and drove the rest of the way home no issues.

When idling it reads at 210* and while on the highway it is around 190*.

I got a new fuel filter for it, but I can't get the thing to unscrew to replace it. I have tried and tried and can't get it off. Another issue I noticed is the oil pressure is at (what seems to be low) 25 psi at idle and will get up to the 70-90 range at higher rpms. I doubt it is related, but wnat to give all the info) Idle rpm is 5-600.

Is this from vapor lock in the fuel line? The fuel line running from the filter to the carb was pretty warm to the touch. What I do to not get stranded anywhere anymore from this?

 

I have had a few vapor lock (including the 390 in my '48) and I put electric fuel pumps on them and that fixed it every time. No need to remove the mechanical pump unless you just want to.

 

So with the electric pump is it as simple as hooking it up to keyed 12v and running a line in and out? I assume I need to bypass the mechanical pump and put an inline filter on. Would this one do it? Precision Fuel Pumps E16049 - Electric Fuel Pump | O'Reilly Auto Parts

 

Apparent vapor lock can be caused by several other things also. A small air leak in or around rubber lines, old rubber lines getting soft and sucked shut, dirty pickup strainer, dirty fuel filter and weak fuel pump are on the list. If it just started doing this, it may be one of the above.

Agree an electric pump (mounted near the tank as low as possible) can help fix it but there may be another problem.

 

No need to bypass the mechanical pump, in fact a lot of later model vehicles have 2 fuel pumps. You install the electric pump close to the tank. By doing this you are pushing the fuel to the mechanical pump, and if need be, due to vapor lock, THROUGH the mechanical pump and into the carb. That pump should be fine, I use the Mr. Gasket pumps when I don't need a Holley pump.

 

Okay, so I should inspect all the lines, check the pickup, and change the filter and see how it goes. How do I get the filter to unscrew, just more force? If I do all that then I just pop in an electric pump and go. Is that all correct?

 

On another line of thinking....

I had a truck do exactly what you describe when it had a weak coil.
Heat of idling or sitting after a hard run would make it not want to fire until it cooled. Steady cruising and it ran alright.
Took me a lil bit to figure out.

Good luck

 

Coils are cheap, it might as well get one of those anyway. I'll check the things out when I get a break from my current project.