rv8riveter

Howdy all

I have a 2000 Expedition with the 5.4L in it and have some intermittent delayed starting issues I have been trying to fix. Sometimes it takes 3-4 seconds for it to start and other times first key stroke. No engine codes and seems to run fine.

I replaced the fuel filter no change.
I have tested the fuel pressure and get what seems a strange readings;
Key on Engine OFF = pressure ticks up from zero then falls back down.
Engine running = steady fuel pressure of 30 psi.
When engine turned off = fuel pressure falls to zero in about 8 seconds.

What is the best way to test further? How do I test the fuel pressure regulator? Is there some sort of overpressure relief or check valve on the fuel pump?

It seems a leaking injector is unlikely as zero pressure with engine off is a lot of fuel and the engine would have other issues.

Thank you,
Wade

Kattumaram

As I recall the fuel pump is shut down by the PCM if the start command is not issued within a few seconds....eight seconds seems about right.

If you see 30psi KOEO, then the reg is OK.
Test fuel pressure leak-down by monitoring the pressure KOEO, shut down the engine and watch the pressure. It should not leak down more than 5psi in one minute. Pressure falling to zero in eight seconds indicates a leak somewhere or an injector or fuel system check valve....I hope not.

Other members may have more insight....what say you all??

Checked my AlldataDIY for fuel system anomalies. The leakdown, assuming there are no leaks in the system, is due to a faulty fuel pump module or leaky injector. And the fuel pump will be shutdown if no start command is issued within eight seconds.

JimFX4

Checked my AlldataDIY for fuel system anomalies. The leakdown, assuming there are no leaks in the system, is due to a faulty fuel pump module or leaky injector. And the fuel pump will be shutdown if no start command is issued within eight seconds.[/QUOTE]


X2- That is my though- especially the fuel pump. If you have never change the filter before this current change, your pump could have been killed. Imagine trying to drink a slushy with ice blocking the straw (Darn, now I have to go get one). That is a lot of extra pressure.

rv8riveter

Thank you for the replies.

I have replaced the fuel filter at reg scheduled intervals.

When the key is turned on, engine off, the pressure only gets to about 5 psi then immediately falls back to zero, all within 5 seconds. The truck runs normally, rapid acceleration is fine. Hence my confusion.

If it was the fuel pump I think it would have running accel issues.

Since the press reg controls pressure by bypassing fuel back to the tank I was thinking that large a leak could be the seat being worn and leaking by. I am considering trying to find a place to pinch off the return line and see if my pressure goes up. Do you guys see any problems with that test?

If that test shows no difference then that would leave the fuel pump bypass or injectors. I guess at my mileage that it wouldn't hurt to clean and test the injectors and then save the fuel pump for last. Does that sound like a good plan?

Thank you very much for your time and assistance.
Wade

Kattumaram

The return line from the regulator to the tank should be a straight run. If the regulator bypass valve were leaking severely, the fuel rail pressure would never reach 30psi. The fact that the engine runs normally and fuel rail pressure is within limits indicates that the regulator is working. The vacuum line to the regulator lets the fuel rail pressure track variations in manifold pressure to keep a constant differential fuel pressure across the injectors.

A quick test to see if the regulator bypass valve is leaking: Pull the reg and give it a blow test. Bleed the fuel rail of air after reassembly and before trying to start the engine.

My best guess is that the fuel pump module has an outlet check valve that has gone bad allowing the fuel to run back through the pump to the tank when the pump is turned off.

You might test that theory by temporarily installing a check valve in the fuel line between the fuel filter and engine. If that cures the trouble and, if the auxiliary check valve is off sufficient capacity, you may have saved yourself the cost and trouble of a replacement fuel pump module.

lifted98_f150

ive never had to change a fuel pump in an f150... usually its silverados that eat fuel pumps so i am not familliar with the ford but in the chevy's while on a road test with a fuel pressure gauge usually they run about 40 to 45 psi under load and hold pressure for up to an hour after key off engine off and will maybe drop about 5 psi after an hour if the fuel pressure drops off to zero after a few seconds key off engine off that means there is most likely a bad check valve in the pump or just a bad sender unit i dont know if ford has the same design or not but just an idea.

Kattumaram

The systems should be very similar. Fuel pressure control is strictly a mechanical function in the Ford application where the control element is the fuel pressure regulator. I can't find any electrical/electronic interface in the system aside from on/off power and the no-start-command-monitoring auto shutdown.
There is, of course, the crash-generated intertial power cutout switch.

So, barring fuel line leaks and a very leaky regulator bypass valve the only candidates for the pressure loss are injectors and fuel pump module.

rv8riveter

For future reference help.. I finally got around to troubleshooting and had a friend pinch off the return line from the fuel press reg and when I turn the key to ON the fuel pressure reads 35 and holds there.

So replaced the fuel press reg and key on pressure is good. When I turn the key off it now takes about 2 minutes for fuel press to bleed down versus 5 seconds. That could be the fuel pump check valve, but not worried about it.

Thanks for all the replies of help.

Wade