Have any of you delt with bad vapor lock?

1978 f150 351m, 2wd C6 auto.

Will drive fine for a bit then randomly die and wont start. Checked fuel filter no gas it is empty. Well went back at night truck started and ran. This morning tried replicating the issue. Truck ran fine again then after a bit (10 mins of driving) outside temp is 86, it started to struggle to get fuel to the filter from either tank. Took gas cap off no difference. Plumed the hose away from the manifold as much as I could. Then the fuel started bubbling in the filtet and would go from complete none in there to sputreting to back to empty. Im assuming this is vapor lock?

I have replaced:
new fuel pump, fuel filter, sending units, front/ rear gas tanks, tank selector valve, tank selector switch, carb filter, ignition control mod.

 

Could be a clogged sock in the tank.

 

I assume the liquid on the wire loom in the video isn’t fuel that leaked.

See the post I did recently about heat soak at my fuel pump. My filter would do the same thing. Next
time, check the temp on the outlet side of your mechanical fuel pump. You may have a similar
situation.

Otherwise, you could see if the air is coming pre- or post-pump by replacing the segment of rubber hose that connects the metal fuel lines to the pump inlet with a piece of clear tubing. If the air is coming upstream of the pump, you’ll see it. Just don’t leave the clear tubing on for too long. It won’t hold up to the fuel.

 

Ok, here is my thoughts:
You are getting minimal fuel delivery.
It sure looks like air with fuel.
I don't know if your filter is pre-pump or after-pump. Either way I think you have an air leak.

I went out to fire up my 300 six with cranking but No-Fire. _ Come to find out the hose to pump had a split on the lower side.
The new Gates fuel hose seems to get petrified quick these days, so if the seal gets broken, they need re-tightening.

You may be getting enough fuel to start and run at idle, until the float bowl gets sucked dry, because delivery cannot keep up with demand of upper rpm running down the road. In a sense, you are fuel starved possibly because of air.

What I would do to eliminate assumptions, is to remove the fuel tank from your Briggs engine and plumb it in direct to the inlet side of the pump. Secure it firmly and go for a spin to see what the results are.
You have two tanks, plus the connections at the fuel tank Selector switch, then fuel hose connections down-stream from there.

Fuel delivery gremlins are super frustrating.
I laugh to myself because when we have fuel deliveries, the First thing we think of is that the pump is not working properly.
Well, with a pressure gauge, that is an easy one to troubleshoot, and many times the pump is not the culprit.

Keep plugging away and let us know how it is going.

 

One other thing to Check is the rubber fuel lines. I was having similar issues when I would send the engine to higher rpm’s. Found that the rubber lines were softer than they should have been and, in theory, would collapse under high demand. Replaced them all, from the tanks to the pump.

 

Any line between the pump and the tank can collapse. Don't use soft lines. Alosse connection can induce air.

 

thanks
yea the liquid is water I tried the method of cooling down the lines to see if the truck re-starts
how did you check the temp on the pump just with a laster thermometer?

 

I just used the laser thermometer and my hand. When the bubbling would occur, the inlet leg of the pump (like the image below) would be fairly cool, whereas the outlet leg and the base would be too hot to keep my hand on. At that point, I had already checked and/or replaced everything else upstream of the pump.