Is it the fuel pump, or other problem?

[DaleG]

97 Explorer Sport 4x4 SOHC V6
Recently I have been having an intermittent problem with the truck not wanting to start on hot days after making several close together stops, like grocery, dinner, etc.
It will crank and fire but wont stay running, acts like vapor lock. After letting it sit @ 30-45 minutes it will start just fine and run normally. Only notice a slight lag on accelaration that seems to be fairly new.
After searching forums I have tried several things. During this fail condition I switched fuel pump relay, no help. I have been unable to determine if pump runs/primes during fail condition because both times I have been out and near busy highways alone and just too much background noise to hear. Tonight after I made it home I hooked up a fuel pressure guage to it and could hear pump prime and pressure went to about 35psi, key on engine off. I then started it and pressure regulated to 30psi (seems low, is this correct?). I was unable to pull vacuum hose on regulator, hard to get to on SOHC. I then turned truck off and fuel pressure rapidly dropped to around 10 psi where it then stayed fairly steady. I assume this means the check valve in pump is bad but would this also cause the no start when hot condition?
I am actually taking it to the shop tommorrow due to lack of time and expertise in replacing a pump, but I would like some opinions from the experts on here on possibles causes.
Thanks for any help

Dale

 

[dogfriend]

My 97 manual says you should get 35 - 40 psi KOEO (key on engine off) when the fuel pump is operated using a scan tool to run the fuel pump to get maximum pressure. It also says that after turning the key off, the pressure drop in 1 minute should be 5 psi or less compared to the max pressure. (e.g. if you get 35 psi max, it shouldn't drop below 30 psi during the first minute after shutting off the fuel pump).

If you don't hold pressure, the manual says check the FPR (fuel pressure regulator) for fuel in the vacuum line port (bad FPR). If the regulator is ok, then check for fuel injector leaks (need special Rotunda tester for this, common sense says you would be able to read spark plugs). If it isn't either of the above, then the check valve in the pump is probably bad.