As the title says, I've been having fuel issues with my truck. It'll start and run for a while, but eventually dies (as I found out on my way to work lol) and will refuse to start again until it sits for a while. I've replaced the fuel filters even tho they looked clean, and it hasn't made a difference. I have a fuel pressure gauge up by the carb and when I first start the truck, it sits at 6-8 psi, then slowly drops to below 1. I also noticed that the line that runs from the tank to the pump was visibly pulsating; when I pinched the line, I could feel intermittent flow. I also checked the tank for vacuum in case it was a venting issue, but as far as I could tell, there was no vacuum. My only idea is the pick up in the tank is picking up gunk as it runs, then settles when it's turned off, but like I said my fuel filters were clean so I'm kinda at a loss here.

 

I AM GUESSING UR PUMP diaphragm has a tear........strictly a guess........because what else would make the pressure drop.....you got clean filters............
Maybe trash in the needle & seat........

 

Does this truck have evap canister?

 

Could be a weak diaphragm in the fuel pump, but sounds a lot like vapor lock.

Do you run ethanol blend fuel? It is really hard on rubber components in the fuel system, it will soften fuel lines and the rubber diaphragm in the fuel pump and deteriorate them from the inside out. You mentioned the fuel line pulsing and it was soft enough for you to pinch it. I think I would be replacing any rubber fuel line in the system to eliminate that as a potential cause.

Next time you get it running and fully warmed up and it starts causing issues, see if you can touch the carb, if it is too hot to touch you may want to do I did on my '79. I was having a lot of vapor lock issues so I added an insulating gasket (about 1/4" thick) between carb and intake to keep the carb from getting heat soaked.

Modern fuel blends, ethanol or not, have lower boiling points than fuel years ago. If the carb is getting heat soaked it will boil the fuel, and if there is a steel line between pump and carb it can boil inside that line. Vapor won't pump and you lose pressure. Since most cars on the road anymore are fuel injected and run much higher pressures fuel boiling isn't a problem. The added pressure keeps the fuel from boiling and there are return lines send fuel back to tank when it is not needed so it doesn't have a chance to sit in the lines like carb vehicles. Same concept as water boiling at lower than 212*F the higher in elevation you go, less air pressure than at sea level so the water will boil at a lower temp.

Before doing anything check the oil, if the level is higher than it should be or smells of gas real bad, you might have a leaking fuel pump diaphragm and it is dumping raw gas into the oil pan. If that's the case, swap out fuel pump and change oil before doing anything else.

 

I echo the posts about the fuel pump but if your truck has multiple tanks and has the switch on the driver side floor board I would pull that off and clean it.

I had similar issues and it ended up being my fuel tank and then like the six inches of rubber hose that came off it and connected to the fuel line.

it was all jamming up in that selector switch causing intermittent flow followed by it barely running.

in my opinion it was easier to just buy a new tank. I tried the whole nonsense with cleaning them out but it just didn’t work and cost more in time and money to do. Rubber hose is also cheap.

you might drain your tank and see what kind of gunk comes out of it and make your decision there. Followed by replacing any rubber hoses and cleaning out that switch if you have one.

when I had that issue I kept checking the filters and they looked clean to me as well.

 

You can pull the sending unit out of the in-cab tank and look down inside with a flashlight and see if there's any crap in the tank.

 

You can also verify your Fuel System by running it off a separate gas can. Take the input to the fuel pump and run in into a gas can and see how if work. This eliminates the fuel tank and lines, if you still have an issue it points to the fuel pump and carb.

 

it’s already got a chonky spacer and I don’t recall the carb feeling even moderately hot last time it happened. Also the line from the pump to the carb has reflective heat wrap where it runs next to the engine and all the fuel lines are relatively new so unless I’m mistaken I wouldn’t think they’d deteriorate that quickly. As for the fuel pump i have one on the way already but I’ll also definitely take a look at the oil level

 

Ive been meaning to give this a try but I’ve been busy with work lol

 

Unfortunately I don’t have the cab tank so it’s not that simple for me but I’ve been meaning to get a bore scope to look down into my tank

 

Take the f.uel line off @ the carb and crank the engine with the line in a glass bottle. That'll tell you if it's pumping and the condition of the fuel.