Ford Truck ghost problem

[mrfixit]

Another quizzicle... You start your late '70's ford truck with the big 460. It runs great. you drive for about 10-15 minutes and it sputters and dies. You sit for a minute, crank it and it starts right up, and dies another 5 minutes down the road, and you continue this way until you reach your destination, no matter how far.
Fuel is fresh.
Fuel level is good.
Fuel pump runs perfectly and puts out good pressure.
No kinks or rust in or on fuel lines and lines are in good shape.
Fuel Filter is fresh and clean.
Ignition module is brand new.
plugs, wires, cap, rotor, etc all fresh.
Timing is set correctly.
all mechanicals are sound.
What was wrong?

Tip: This problem was repaired for less than ten dollars.

 

[surewhynot]

Does it involve throwing a wet rag over the ignition module to keep it cool?

 

[mrfixit]

No, the ignition module works AOK...

 

[econo61]

either the stator or the coil.

 

[mrfixit]

Those were fine as well...


It was fuel related, and NOT the pickup screen, either...

 

[john112deere]

Gonna guess the air vent in the gas cap was plugged.

 

[mrfixit]

Good guess, but no. I have had that happen in another vehicle, tho!

 

[Fellro]

When you say the fuel line is in good condition, is that visually? Because the line can degrade internally while still looking good on the outside. The inner lining can fail, and act basically like a check valve, blocking the fuel. That happens sometimes with brake lines, except it locks the pressure on, keeping that particular brake applied...

 

[mrfixit]

You were definitely on the right track with that.
The interior of the rubber line had begun to degrade, and the particles of rubber were temporarily clogging the fuel inlet on the carbeurator. The inlet acts as a filter itself, with tiny orifices for fuel to pass thru. Drive a short distance, the fuel under pressure clogs the orifices. Shut it off for a moment, the particles float away, until the flow starts again.
It was a VERY annoying and persistant problem until one day I pulled the inlet and blew it out into a white cloth... then I saw the black flakes.

 

[blacksnapon]

I stayed out of this one cause I've had one that had vacuum lines switched on the evap that caused the full vacuum to collapse the tank forcing the fuel pickup out of the fuel. I had one that the insulating compound wasn't used on a replacement ign module (had 'em use regular silicone too) All had the same symptoms. Good find on the fuel line though!

 

[mrfixit]

Ahhh, but the insulating compound is for LATER modules, hehe... not the old 70's fender-mounts.
I figured you were staying out just to make it fair, anyway

 

[Brian_B]

On one of the old trucks on "the other site" a pencil eraser in the gas tank did a similar thing.

It would plug the fuel flow, kill the engine, and a while later it would start up and run fine until the eraser got in the way again.

 

[mrfixit]

My brother-in-law insists that an egg in the tank does the same thing... the gas chemically "cooks" the egg, and occasionally it gets sucked up to the pickup tube.

 

[A_G]

has it already been answered.

I say corrosion in the tank causing a clog at the fuel pump/ carb.