Proper fuel pump pressure?
06-29-2015, 02:54 PM
#1
Proper fuel pump pressure?
1986 5.0 F150. With EFI. What is the proper fuel pressure at fuel rail? I am getting 40 psi initially with key turned on and then 32psi with engine idling..Is this correct?
Last edited by saemetric; 06-29-2015 at 03:34 PM.
07-04-2015, 01:41 PM
#4
Senior Member
Key on pressure: 30-40 psi
Running pressure: 35-45 psi
-and-
Pressure remains 35-45 psi for at least 60 seconds after turning key to off from running.
07-04-2015, 04:54 PM
#5
It's a little low, but enough to run the engine. Try changing the filter, that might get you a little more pressure at the rail.
EFI V-8's run at 30 to 45 psi, as do 95 - 96 I6's. Earlier I6's run at 45 to 60 psi
Your motor will run between 30 and 45 psi. Higher up in that range is better. It has to do with the spray pattern coming out of the injectors.
What should happen is that you get an initial pressure when you turn the key to on. Then when you start it and it's idling (high vacuum) the vacuum being applied to the fuel pressure regulator should open it allowing some of the pressure to bleed off and return to the tank and you will have lower pressure at the rail - again, it's about the spray pattern.
Then as you open the throttle a little (low vacuum) the vacuum will drop, the regulator will close and pressure should climb back up.
On my truck for example ; I turn on the key, it goes right to 42. Start it, it drops to 38 - open the throttle a little, right back up to 42. That's what it's supposed to do. That's a good healthy system. As I said, yours is a little low, but not so much that you would have problems with the truck running/not running. Could be a pump getting weak or just a dirty filter.
EFI V-8's run at 30 to 45 psi, as do 95 - 96 I6's. Earlier I6's run at 45 to 60 psi
Your motor will run between 30 and 45 psi. Higher up in that range is better. It has to do with the spray pattern coming out of the injectors.
What should happen is that you get an initial pressure when you turn the key to on. Then when you start it and it's idling (high vacuum) the vacuum being applied to the fuel pressure regulator should open it allowing some of the pressure to bleed off and return to the tank and you will have lower pressure at the rail - again, it's about the spray pattern.
Then as you open the throttle a little (low vacuum) the vacuum will drop, the regulator will close and pressure should climb back up.
On my truck for example ; I turn on the key, it goes right to 42. Start it, it drops to 38 - open the throttle a little, right back up to 42. That's what it's supposed to do. That's a good healthy system. As I said, yours is a little low, but not so much that you would have problems with the truck running/not running. Could be a pump getting weak or just a dirty filter.
07-06-2015, 10:52 PM
#6
Rechecked pressures: 40 psi ignition on, 33 psi running at idle AND off idle, 40 psi with vacuum off regulator. Seems like fuel pump OK but has some wear to it(98000 miles). FP regulator seems OK but could be better to bring off idle pressure up a bit. Truck seems to be running fine so will leave as is for now. Does this sound like a reasonable diagnosis?