'86 F150 302 EFI Fuel Pressure Loss
 

My '86 F150 302 EFI has a fuel pressure problem. When started cold, pressure is 35psi, but after 10-15min. of driving/idling drops to 10psi; then runs rough/no power. If try to re-start after short time (~30min.) still has low pressure. If wait several hours, starts out at 35psi again. Replaced frame (high pressure) fuel pump, relay, fuel filter. No change in problem. Problem is same on either of the dual tanks. Anyone have an idea of what the problem could be?

Pull the vacuum line off the fuel pressure regulator. If there is gas in the line, then replace the regulator.

Thanks for suggestion Franklin2. Going to repair shop to bring it home again - hopefully last time for a while. I understood they discovered a hole in the inside tank line that caused the fuel pressure loss. I don't know why it would cause a drop in pressure after 10min, but they said the tank pump was just pumping the fuel back into the tank. Hopefully it's fixed now.

Steve

Picked it up today. Hole in inside tank line was problem - the line was badly deteriorated and falling apart. The hole was about size of dime. Runs great now.

so this was a line inside of a tank that was the problem?

What a pain that must have been! I've read a lot the last few years about the increasing problem of the alcohol in today's fuel blends destroying fuel lines in older vehicles like ours. There's a unique type of fuel line for use on the INSIDE of fuel tanks. Did they mention that to you? If your invoice shows a 12" piece of fuel line for what seems like way too much money, that would be it.