Fuel Pump

I need to know what engine size you have in truck to look over the right wiring diagram so I can try to help with what might be going on.

It is the 4.6 L V8

Ok next time it won't start I would like you to check the inertia switch. It is on the right side (passenger) under the dash, see pic below. Once you find it simply push the white or red button on it and see if it starts. Otherwise I would have to say we need to check the wiring to the pump or check for power to and from the relay with a digital multi meter. Let me know what you find and we will take it from there.

I have checked the Inertia switch, it is fine. I have learned something that might help you. I can keep turning the key from the off to run until I hear the pump run, then it starts. Sometimes it takes several times, but once I hear it run it starts right up.

Have you checked out the PCM power relay? This is the switched power source for the fuel pump relay. This is in the junction box under the dash. If you have a digital multi meter then check if term 86 or the white wire with the light blue stripe is getting power as you turn the key on.

Now the pump will not engage at all. I will test the wire you told me about tomorrow. Is it AC or DC?

It is all DC power. Let me know what you find and we will go from there.

I checked the relay, it is getting power. I can feel it clicking when the engine is turned over. I will check the wire going to the fuel pump. Will it be the white wire with the blue stripe? Where in line would be the best place to access it? Thank you for your patience, I will add some more money to the forum for you.

It shows the wire to be pink with black stripe that powers the fuel pump. Let me know what you find and we will go from there.

The Fuel pump is definitely getting power. My meter reads the pink with black stripped wire as getting power and I can hear it click when the key is turned but it does not run.

Ok so when it won't start does the pump get power? Have you replaced anything? Have you checked for spark?

I have a 2002 ford expedition, 4.6 v8, pulling up in my driveway and the truck went dead. They told me it was the fuel. So i replaced the fuel pump and the filter, but it keep blowing the fuse under the hood

Which fuse?

When I try to start my expedition it will crank but it won't start. I have determined that it is a fuel problem since there isn't any fuel at the rail. I have replaced the fuel filter,fuel pump, fuel pump driver module, crank position sensor, and both cam position sensors. I have also pulled the central junction box and checked the built in fuel pump relay to see if it was bad and it wasn't. What else should I be doing to get fuel to the engine

The first thing you should be doing is using a fuel pressure gauge to know for sure what the pump is or isn't doing.
Check the Inertia switch to see if it has been tripped.

I checked the inertia switch and it wasn't tripped. I also checked to see if I was getting any voltage to the inertia switch and I am not. As far as the fuel pressure, when I pulled the main fuel line off of the rail and cycled the pump several times,there was not any fuel coming through the a in line. The only reason I pulled the main line is because I can't seem to be able to find the Schrader valve anywhere on the fuel rail.

I don't know how you can know an internal relay is good or not. You're just going to have to track it down with the wiring diagram.

I have the diagrams and I tried bypassing the fuel relay to see if that worked and it didn't. This is what leads me to believe it is something else.

That just makes no sense at all. You say you have no power at the Inertia switch and that comes directly from the relay and you say you jumped that out which would have put power directly to the Inertia switch. You're doing something wrong here. The fuel pump relay is not even accessible.

This is what I used as a guideline. I understand that the fuel relay is not accessible that is why I tried to jump the wires that come from the relay.

When Driving or just sometimes trying to start the engine, there is a loss of power to the fuel pump relay coil.

What would cause a situation where the Engine Control Unit
(Computer) to not send the signal to the relay?

Sometimes the engine will start shortly after going dead, more often than not it wont. I have manually thrown the coil switch to start the engine and currently, the engine is starting normally.

Just do not want to have it shut down again while driving.
Is there a sensor that could be causing this?

I don't know where you got that diagram but it is different from the one I got from the service manual for that vehicle.

You nee to be very careful what you are jumping there because you can fry your PCM in a heartbeat,

see if relay prongs have corrosion on them if they do clean off what you can and put dielectric compound on them.

That diagram doesn't even have a FPDM in it.

We have already determined that the computer is not sending a pulse to the relay. We are thinking that it is a weak or worn Crankshaft Position Sensor.

Ok so let's say I was stupid and fried my pcm. Then why would my truck run off an external fuel source after I tried all the other stuff.

Yes, is the crank sensor is faulty the computer will not send a signal to the fuel pump replay. Is there spark at the plugs when this happens? Is so its not the sensor.

Please let us know what you find so it will help others.

Best, Ken

Nobody said you fried your PCM. You ARE using the wrong wiring diagram and you need to stop trying to jump things in that circuit because you can short out the smart junction box also.
Do this, try applying power to the white wire at the Inertia switch and see if the truck starts.

Not sensor because spark would not be present. What we did was removed the relay and used a jumper wire from the 15 amp fuse used by the fuel pump and jumped it to the relay. In that way, only when the ignition is on will the fuel pump work. Crappy way of doing things, but better than having the car shut down as you drive down the freeway with no steering, etc. The problem was sporadic and I just didn't trust it anymore. Probably was the computer ….?

no it may be the smart junction box as the relay is part o f it there was a problem with those from 2003-06 you could wire in another relay that stands alone to fix it correctly.

Car doesn't start on first attemp. Engine is turning over, but it won't start. I turn the key to off and retry. It starts on second attemp. Is the fuel pump relay going out and needs replacing?
Thanks
Kevin

Your going to have to hook up a fuel pressure gauge to see what happens when it's shut off. It should hold pressure for a good period of time. It may have a bad check valve in the pump causing all the fuel to siphon back into the tank.

Sometimes it will not start and other times it starts right up and runs perfectly. Whenever it doesn't start, it cranks over like crazy, however it reads no fuel pressure at the rail. When it does start, it reads plenty of fuel pressure. The battery and connections have been cleaned thoroughly, the fuel filter and fuel pump both have been replaced. Also, the fuel pump relay has been replaced.

Could this be an electrical issue? Anyone have an idea of what it could be? I have heard that it could be the actual fuse box itself, but I'm not sure if that would fix it or not. I have inspected the circuit board inside of the fuse box and it does not seem to be burned anywhere, but I'm not sure.

Can someone please help?

Thanks in advance!

Also, by the way, I have checked and it is not giving any codes either.

And, this might be just coincidence, but it seems that when it does this that if I bang on the fuse box with the bottom of my fist 2-3 times; then it will start. I'm not sure if that has anything to do with it or not.

the fuse box may not be making contact, try dielectric grease on prongs of relay and tweek a tad check for corrosion as well

Thanks for the answer. Actually, it was the PCM relay that was replaced as I am told that the fuel pump relay is built into the circuit board of the fuse box. I have noticed that the PCM relay seems to get pretty hot. Do I need to pull the PCM relay back out and apply dielectric grease on the prongs of that one? Is that the one you're talking about or should I apply it to all of them?

no I forgot about this, this fuse box goes bad and most mechanics will put a new relay in for the fuel pump instead of replacing the fuse box it's the smart junction box that does this . changing the pcm relay won't help

Ok. So, those are the classic symptoms of the fuel pump relay failing or starting to fail? Then it is not sending power to the fuel pump sometimes and sometimes it does? Then, that would explain why when it is just cranking and not starting, that I read no fuel pressure at all on the rail. Do the dealer mechanics replace the relays? I live in rural Northeast Georgia and am not sure of a mechanic to check with about this.

no the dealer will charge about $1500 to fix this as it needs the smart junction box replaced. I can't find the tip from one of the mechanics wrote on here. but you can just jump the box by having one installed or getting a used one.......