My '87 F-150 with the 4.9L six has always been hard to start hot. Like last weekend it was fairly warm outside, in the 80's I think, I drove it about 20 miles shut it off for about 20 minutes or so and it would barely start back up (cranks but won't fire). Once it's running it runs fine.

If it's not good and hot it will start up just fine. In the past, I have noticed that when it cranks but won't fire, if you cycle the key to on a couple times it will fire right off.

So anyways, I got a fuel pressure gauge and connected it and started going through the tests in the Haynes manual. With the fuel pump running and the engine off it shows good pressure, 55 psi. With the engine running its with in specs at about 48 psi. But when you shut the engine off, the pressure drops immediately. Haynes said to crimp off the supply line and the return line in two different tests to see the effects on the drop but neither seemed to affect it.

I have recently replaced the fuel pressure regulator, tank selector valve, and the injectors were replaced with rebuilt ones.

Anybody have any ideas? I've thinking its time for a new in-tank pump, but was hoping that these fuel pressure tests would verify that but I'm still not sure.

Thanks for any advice

 

Do you mean when you turn the engine off and key off? because key on is what turns on the fuel pump, with the key off there shouldnt be much fuel pressure because the fuel pump wont be on

 

Yes, key off and the engine off. Haynes says that I should hold pressure within 5 psi for about a minute after shutting the engine off. Mine drops right away.

Thanks