Truck wont start,

[90rangersuper]

Aright here i go again, truck quit running on my one day, no humm from the fuel pump, checked the inertia switch, not tripped so i replace the fuel pump, before i bolt the straps on i wanted to check to make sure its working, go turn the key to on to hear the humm, no humm, she still wont start, tried the inertia switch in both positions no go, have not checked voltage at the pump yet just wondering what other things i should look at before i start to part the truck out

 

[KELLY88]

Fuel pump relay or bad grounding wire?

 

[90rangersuper]

hey kelly, where might the fuel pump relay be located at

 

[90rangersuper]

ok i checked voltage at the plug that hookes in to the pump, i got with key on 1.13 volts, all the fuses are good and i hear like a relay click about 2 -3 seconds after turning the key on, any help would be great

 

[KELLY88]

hey kelly, where might the fuel pump relay be located at

Not sure exactly on your truck. But you could also try testing the big fuse in the fuse box under the hood. Seen them cause this kind of problem before.

 

[Psychopete]

Keep in mind that there's more to the circuit than just the relay and inertia switch. The fuel pump relay is controlled by the computer. If the computer relay is malfunctioning, or not getting power, or computer is not powering up, the fuel pump relay will not get energized. The first thing I would suggest is that you might verify that the computer is functioning first.

Pete

 

[rangerrager]

i would double check the relay under the hood

 

[Earl43P]

Locate the fuel pump relay (on the fender?) and replace it it with one just like it, probably right next to it.

 

[90rangersuper]

checked under the hood, no relay at all, i am going to buy the relay today, if anybody knows exactly where the relay is located that would be great and save me some time

 

[90rangersuper]

i replaced the fuel pump relay and that did not fix the issue, i am thinking this is a grounding issue, where would the fuel pump be grounded, i am at my wits end with this truck, if anybody wants this truck let me know

 

[Earl43P]

I'd look all over the fenderwells, under the hood.

That's where Ford traditionally puts them. I don't know about 90.

To verify that your ground is the problem, check that same voltage at the fuel pump plug, but use a bright shiny scraped spot on the frame, then the chassis as your ground point. If at any other ground point, you get Battery voltage, your ground is bad.

It could be as simple as your engine to chassis or chassis to frame ground is bad. But I'd expect other stuff to not work, if that were so.

 

[naford]

Haven't i read in TRS where others have had a bad inertia switch? I'd check for voltage there.

 

[90rangersuper]

still dont have the fuel pump humming, i have replaced the pump and relay, i have 12 volts at the fuse and 12 volts present at the relay however after the relay at the inertia switch there is only 2 volts present when i kick the key on and at the fuel pump there is 1.7 volts constant with the key turned on, no voltage with key off, everything else works on the truck just the damn pump, ANY help would be great

 

[Psychopete]

still dont have the fuel pump humming, i have replaced the pump and relay, i have 12 volts at the fuse and 12 volts present at the relay however after the relay at the inertia switch there is only 2 volts present when i kick the key on and at the fuel pump there is 1.7 volts constant with the key turned on, no voltage with key off, everything else works on the truck just the damn pump, ANY help would be great

On the older OBD-I systems, there is a way to trip the fuel pump to run all of the time on the diagnostic connector. Please note that when the key is turned to 'Run' only, the fuel pump will turn on only twice for 2 seconds. It might be helpful to test w/ a test light as opposed to a DMM so that you can visually see when it's turning and not have to rely on actually looking at a small screen.

Are you sure you had a good ground inside of the cab to the chassis from the inertia switch? Were you able to verify 12 volts right after the relay? If you have 12 after the relay to the inertia switch, but not before the inertia switch, you might just have to run a new wire from the relay to the inertia switch (not unless you want to dig for it in the main harness). If you're not getting anything out of the relay, or it's not clicking, it's possible that the relay isn't getting grounded from the computer.

Just some thoughts..

Pete

 

[90rangersuper]

update

i was working on the truck and i tried a few things, first i bypassed the inertia switch, no luck, checked the grounds, all seemed good, then i bypassed the fuel relay, between the 12v and the line to the pump and guess what, the fuel pump came on. i though then the computer was bad so i put the old one i had from before i put the manual in there, nothing, the tan/green line i believe is the computer control for the relay, i checked that line for shorts - none hopefully somebody has seen this and can offer some more advise