Been chasing this hard start when warm problem.

Read a great fuel system sticky on this forum and found the following.

when power is turned on, the fuel pressure shoots to 40psi, there is an audible click and the pressure drops to 0psi.
when cranked, the pressure climbs until the engine starts.
At idle, it gives me a normal 31psi.
Vacuum hose removed from Fuel Pressure Regulator FPR and I get an expected jump to approx. 45psi.
Manual vacuum applied to FPR at idle results in 22psi required to bring fuel pressure back down to 31psi. I assume that this 22psi vacuum represents an equivalent to my manifold (22 manifold vac)?

so, is it normal for the pressure to spike to 40 then drop to 0psi when powering up without cranking?

PS- when I first applied the fuel pressure tester, the engine was stone cold. At that time I got only 5psi when the power was applied without cranking. It started on the second turn and went straight to 31psi.

Thoughts?

 

Do you smell gas when you take vacuum line off regular? Some time regular do go bad.

 

It most likley the pump. That's exactly how they go out, - thy begin to freeze or lock up randomly. Check the relay just in case, but yea, prob the pump (typical).

 

I can't find any specific reference material that tells me what the normal operation looks like on a fuel pressure testing gauge.
What part of my IP makes you suspect the pump?
When you turn the key on, is the pressure supposed to go up (to the 40psi
in my case) and stay there during the cranking of the engine?
Also, is the pressure supposed to drop immediately to 0 psi when you turn off the engine?
I was always under the impression that the fuel systems remained charged to some degree even when off.

 

Went ahead and changed out the Fuel Pump Relay last night.
Still no change.

I can hear the fuel pump prime for about a second and a half with my ear to the open fuel port.
-When the engine is cold however, I get no initial pressure with the KOEO.
As you crank the pressure climbs and the engine catches quickly and runs with a consistent 31 Psi.
-After reaching normal operating temp and shut down for a couple of minutes, in the KOEO position I get a quick pulse of 40 Psi then an audible click and the pressure drops to 0 Psi. (this only takes about 3 sec)
-When warm like this is when its hard er for it to catch when cranking but always goes to 31 Psi when it starts.
-I spent yesterday reading as much as I could find about electric fuel pumps. I understand that with the KOEO, there is supposed to be constant start pressure that drops to idle pressure when the engine starts.
What I don't understand is how the pump suddenly kicks back in during cranking and runs fine while the engine runs. It's obviously a pump issue now that the Fuel reg and fuel relay have been eliminated I just want to understand whats going on with the pump.
Nothing I've read addresses this kind of situation.

 

The fuel pump doesnt stay on when the key is on. It comes on ford about 1.5s to prime the fuel system. The pcm doesnt energize the fuel pump relay until it see's a crank signal from the crank sensor.

You have a bad pump. pressure for a v8 at idle should be around 32-36 with vacuum applied to the regulator. When vacuum is removed it should be around 40 psi.

 

What does the computers say the coolant temp is at when engine is warm.

 

Sam, in answer to your previous question, no fuel smell from pressure regulator or it's vacuum hose.
Haven't actually looked at the temp on my code reader when at operating temp before start. gonna do that this weekend.

CarCrazy...what you described above as normal operation is exactly what my pump does. The only time I have a start issue is when its Warmed up.
I have a Motorcraft pump in transit right now. But before I tackle that job, I wounder if an ECT sensor would give me this issue? This is obviously temperature related some how.
Might just switch it out first as it's only about $20.00

I'll let ya know what happens.

 

Do you have access to a scan to look at the pids? A bad CHT could cause the issue you are having

 

I have had a few trucks say the coolant temp is at -40 when motor is fully warmed up. They are hard to start.