Vapor lock or Faulty fuel pump?

[Ohiotinkerer]

Just reminded me of a problem that I had that was opposite of that. My bump had a non vented cap from the PO and when I would drive it in hot weather the tank would build up pressure and push too much fuel thru and stall the truck out - it did that too me driving 65 on a 4 lane highway when I was passing a semi which was not fun. I finally figured it out when it would do it during the day but not at night when it cooled off - if you pulled the cap on a hot day it would blow it off into your hand it had so much pressure on it so I got a vented NOS cap and haven't had a problem since. Just thought I would throw it out there as something to watch for!

[tsherry]

Haven't read all replies, so apologies if this has been covered.

Have you replaced all of the rubber lines, including the soft line between the tank and the hardline? The fuel line as an outer shell, a nylon web reinforcing it, and an inner liner. Ethanol fuels can soften the inner line, cause it to separate from the nylon and outer, and suck shut . I've had this happen on a half-dozen cars now, all old, non fuel injected with original or 'old' replacement lines.

That said, any fuel system rehab for me starts with dropping the tank, cleaning it, sealing it with a kit like that from POR 15, replacing the rubber lines, and usually replacing the old fuel pump and a carb rebuild.

Accelerator pumps on Fords with ethanol sitting in them over time will resemble a screen door, not a diaphragm. Source of many a case of hard starting.

[tsherry]

Get rid of the plastic fuel filter. Those have burned down more vehicles than you can believe. Get one with a metal case and change it annually if you're daily driving it.