My 84, carb, F250 with 7.5L, just started this problem. It will start, and run for approximately 30 seconds, then die. I can restart it, and even giving it more fuel, it still only runs for about 30 seconds or so. When I try to restart, it does seem to take awhile, so I figured it was starving for fuel.

After looking at manual for the truck, I tried to test the fuel pumps, by disconnecting the starter from the starting cycle, and turning the key to start. (I believe it has the "Hot Fuel" system) I do not hear any thing from the fuel pump. Can't seem to find the fuse or relay that would control this. Any ideas?

It was running great before this started, so I am perplexed.

Tim

 

I have an 85 F350 7.5L dual tanks, my fuel relays are in the engine compartment, driver side near the hood hinge. There are two, one for "during start" and the other for "engine running".

Lets start with the "hot fuel". Pressure line goes to carb, there is a tee in the line. This tee has a small hole drilled in one side that goes to the return line. This circulates the fuel and prevents "hot fuel". Hot fuel can cause vapor lock by boiling the fuel.

Pump power. There are two complete seperate power systems that provide power to the pumps. The first is for "while cranking", ther is a pink/white wire coming of your start relay that goes across the top of the radiator over to the relays on the drivers side, it provides power while cranking. Once the engine starts, power is supplied through the inertia switch, then the oil pressure switch and then to the tank select relay on the driver side. If you don't have dual tanks, it might be a little different.

So now for what I think is wrong. I would check the oil pressure switch. When you crank, the first system will provide power. When you release the key, it switche to the other system. It requires atleast 15psi of pressure to close the switch and complete the circuit. Other things could be the intertia switch or one of the fuel relays is bad.

If you have a single tank, I think there is only one relay.

Good luck

 

mstarr:

That is a great starting point, thanks. I do have the dual fuel option, and I can hear the switch changing from one tank to the other, but was not aware of the oil pressure switch.