Hey guys, I’ve recently replaced the fuel pump and fuel tank pressure sensor in my 99 ranger with 2.5 L engine. Still cranks but no start. No fuel is being pumped from the fuel pump. When testing power to the fuel pump with a meter and considering the proper wiring diagram, the meter read -144mV. It seems kind of odd to me and it wasn’t just an erroneous reading because it read exactly that much everytime I cranked it over then went back to jumping around 20-50 mV like every meter does. I’m wondering if a particular sensor could have failed and is causing the engine control unit to electronically deactivate the fuel pump. I’ve checked the inertia switch, fuse and relay for proper functionality.

 

Welcome to the forum

Fuel pump is only powered for 2 SECONDS when key is turned on, just 2 seconds, but it does this EACH TIME key is turned from OFF to ON

Power path:
Battery(positive)------------------Fuse------------FP Relay----------------------inertia switch-----------------------------fuel pump

The computer(PCM) grounds(activates) the FP relay when it Boots up, but just for 2 seconds
PCM then waits for RPMs to be above 400(engine started) before it Grounds FP relay full time

PCM monitors FP voltage when key is on, that circuit will show 5-7volts on the FP wiring, AFTER initial 12volts for 2 seconds, the 5-7volts has NO AMPS so doesn't power Fuel pump, just PCM monitor voltage

If new fuel pump is not Motorcraft brand then it may be bad out of the box, test it by jumping 12volts and Ground to it

In the passenger side cab foot well, maybe behind kick panel, there is the inertia switch, it has fuel pump 12volts passing thru it, so you can test voltage there
It is a smaller black plastic box with a RED button on the top, button will POP UP in an accident cutting power to fuel pump

 

Okay this is the second fuel pump it’s had, the inertia switch isn’t triggered either but I will check power to it when I get home. What could be the issue if I am able to get the pump working by jumping it?

 

You hadn't mentioned "jumping" 12volts to the pump.

So explain, 12v from the battery positive terminal?
To Fuel pump connection on the gas tank?

Or from where to where?

 

Sorry, miscommunication. I meant, IF I am able to get the pump working by means of jumping it(I haven’t jumped it yet but I’m saying IF), then what else could be the issue? Also I failed to mention but one of the spark plug wires is missing as well so I’m not sure if the engine management can see that and isn’t activating the pump.

 

You know where inertia switch is

Pull off its connector, it will have a Pink/black stripe wire, this is the wire to the fuel pump, connect it to battery 12volts and you should hear pump come on, it is not quiet, makes an easy to hear HUMMMM

If so pump and Pink wire are OK
If not then you will need to lift the bed up, or back, to get to the pump



You can jumper at the fuel pump relay, but need to be careful of which terminals you jump
You need a Volt Meter or a 12v test light for this, no other option

Ford used 2 different relay types, a standard and micro

Standard 12volt relay pins look like this: https://i.pinimg.com/originals/30/8a...8e10c0c120.jpg

micro relays look like this: http://www.gtsparkplugs.com/images/m...lay-wiring.jpg

So easy to identify which is which

Slots 30 and 87 are what you want
With key OFF
Test 30 and 87 with grounded volt meter or test light, one will have 12volts, thats from the Fuel Pump Fuse, if no 12v then fuse is bad
The OTHER one will be connected to the wire going to inertia switch

Key is STILL OFF, put jumper between 30 and 87 and fuel pump should come on


No, missing spark plug wires or other engine parts wouldn't cause no fuel pump issues

 

Well the truck bed is off already since the pumps been replaced. I jumped the fuel pump right at the connected to the fuel pump and got nothing. Was jumping with jumpier cables and some thick wire. Power source was from the battery of my running car. No fuel, no noise. Guess I’ll be buying a motor craft pump and hangar assembly (the whole assembly since this new pump came as an assembly so it’s probably all screwed up). Any other regards you might have before I wrap this thing up?

 

If you have the bed off then just test the pink/black wire on the FP connector with a volt meter or test light, should have 12v for 2 seconds with key on and then 5-8volts after that, that means wiring is OK

Inspect filler tube for cracks, also any of the EVAP air/vacuum lines, these "rubber" hoses stay in one position for 20 years, so when you move them they can crack

 

That’s what I was saying in the original post, whenever turning the car on and cranking the engine over the meter said -144mV and when testing continuity to ground I had 4.5 ohms on the ground but this could be because I had the truck hooked up to my car via jumper cables. I didn’t understand that but at the same time when putting power straight to the fuel pump it’s not working when it should.

 

And meter is set for DC Volts?

 

Unless I made an amateur mistake lol I’ll have to check again I suppose. Between the truck needing to be jump started and the battery terminals needing replacement (they’re kind of loose) it takes three people just to hold the jumper cables, crank the truck over, and read the values with a meter.

 

I figured it out this weekend. Just started over in my diagnosis process. Had 0 volts to the pump but the ground was good. Checked fuel pump relay fuse and it was good. Wasn’t getting power to the control side of the fuel pump relay. As I was referring to the wiring diagram I saw what’s called the PCM power relay that send power to the control side of the fuel pump relay when activated. The control side of the relay also had no power. Sure enough there was another fuse for that particular relay and for some reason it was missing. Put the correct fuse in and my ole truck started right up. I’m ecstatic. Thanks for all your help RonD.

 

What fuse? -<><

 

its been a while since i repaired the truck, but i believe it was the fuse for the powertrain control module “main” relay. Pretty sure its referred to as the PCU main relay but i could be wrong. I hope i was able to help!