Well I have read almost every post on why my truck runs fine, but every once in a while it will crank but will not turn over. One solution that seems to be fixing or delaying the issue is turning the ingition to "ON" a few times then it starts. I have been listening for the pump to prime and when it doesn't prime of course it will not start. Rolling the key a few times, I here the pump start to prime. So, my question is, when rolling the key, what is this action accomplishing? I understand that the pump, a few censors and filter replaced, but why the key turns?

Please forgive my ignorance. First Ford and my automotive knowledge has lacked since buying 2 new vehicles.

Any reply will be helpful.

 

It will crank but not turn over? Or did you mean it will crank but not start.......? When is the last time your fuel filter was changed?

 

Engine turns over but doesn't try to start. I just bought it used in October and I am slowly working my way through the truck. The filter should probably be changed.

 

Gotcha'....yeah...for sure get that filter changed.

 

Here are major starting events that happen as you move the ignition to the RUN position.
The computer is powered.
The fuel pump timer is pulsed for about a 1 second pump run, then shuts off. This action does the most to pressurize the fuel rails for starting.
As you begin to crank over the motor, the front crank position sensor sends rotation signals to the computer.
As this happens the timer circuit that controls the fuel circuit turns on again and stays on as long as the motor is turning over.
This provides fuel on a continious basis to the fuel injection as the motor runs.
.
Comments:
If you were to run out of fuel in the tank and needed to prime the fuel rails, several on and offs would run the pump enough times to apply fuel pressure again in a fault free system.
The pump system has a check valve to help prevent loss of pressure on a short time basis helping instant start. If the check valve does not hold well enough, longer cranking time could be the result.
In the system, is a fuel pressure regulator that drops the system pressure from as high as 85 psi to about 39 to 44 psi +/- for normal injector pressure use. This regulator also is under vacuum control for one reason only and that is to reduce fuel pressure under high intake manifold vacuum and at idle when the pressure and fuel feed is least needed. At this point, the injectors' fuel metering is reduced do to low demand at idle. Fuel injectors are delivery rate sensitive vs fuel pressure so need to be pressure controlled to close limits in psi.
.
What you need to do is some testing of the fuel pressure and how it acts in determining if there is an issue in fuel delivery as referenced to the above operation.
Good luck.

 

Blue...you're my boy BLUE!! That is the info I was looking for!! Keep up the good work!!