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SOLVED - No fuel pumping!

Adam Robert

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I recently purchased a 2002 Sport Trac as a project. It had sat for some time and could not start. I knew I would need to take the engine out, but I did some work first and was able to get it to fire (though only for a moment before shutting it off).

NOW I have taken the engine out, made repairs and ensured the timing was correct. Put it all together and back in but… now it will crank but not fire. I have worked my way through figuring out that the cause seems to be because there is no fuel getting pumped.

Everything looks right and the fuses/ relays seem fine. The inertia switch is down and I even knocked it loose and reset it. Can anyone think of a sensor plug I may have missed that could cause the pump not to run? I feel like it almost certainly has to be something stupid and small, but cannot figure out what that could be. Surely if it fired before the engine came out, the pump itself would not be the issue.

Please help, thanks in advance.
 



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Fix4Dirt

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if it fired for a moment, that doesnt garuntee long term functionality, how old is it? fuel pump relay good? no pats issue (light on dash), if you turn the key to the run pos, do you hear it prime? is everything grounded properly? thanks!
 






Adam Robert

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if it fired for a moment, that doesnt garuntee long term functionality, how old is it? fuel pump relay good? no pats issue (light on dash), if you turn the key to the run pos, do you hear it prime? can you test rail pressure? thanks!
Hey buddy, I appreciate you hopping on to help another one of my many issues.

- No confirmation on the pump itself. It does not prime when I turn the key to the ON position. Since I was able to get it to fire prior to taking the engine out, I’d have to believe it works and would like replacement to be a for sure final step.
- The fuse is good. I swapped relays and no change. I used a test light on the relay inputs and all inputs appear to be functioning correctly.
- I can tell there’s no rail pressure. I discovered this as the problem when I first disconnected the fuel line to the engine discovering it was dry as a bone.


Tomorrow morning I’m going to get a test light long enough to reach the inertia switch. Looking at the wiring harness, it seems that is the last line of power going directly to the pump. If it has power and the switch works, I may have to bite the bullet on a pump. If it has no power, there must be another issue.
 






Fix4Dirt

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no problem, thats what we are all here for!!! if it doesnt prime, then makes sense why theres no press at the rail. give me till tomorrow to think of the reasons why the pump A. could have failed B. isnt getting no power... i wonder can you "jump" the pump w 12v from the obd port... like if you give 12v to the positive lead, i wonder if it would pump. if so, that would lead me to believe bad gound or something leading up to the pump, and would eliminate pump issues. not too sure on this one, and if this would even work! just thinkin out loud here! can you put a voltmeter somewhere up to the harness that goes onto the pup? should b able to telll if it gets 12v...
 






Fix4Dirt

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also, just to confirm- the theft light aint flashing right? just ruing out a pats issue.
 












Fix4Dirt

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alright, ruled that out, thanks! just making sure it wasnt an extent of a prev issue i believe you had mentioned. yeah, jsut let me know if you can test power at the pump, power at relay, and see if you can "jump" the pump (not too sure on this one, maybe someone can confirm if this is safe or not!)
 






410Fortune

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Here is what I would do
Unplug the fuel tank wire if connectoryou can remove it from its clip on the frame rail which gives you enough room to unplug it
Now using battery power or jumper
Box or whatever send 12v+ and a ground directly to the pump
Can you hear it run?

The two largest wires are the pump power and ground

Now check the signal on the truck side with a. Voltage meter.
When key is turned does it try to prime the pump (test for battery power)

Now it should be clear if it is an issue with the truck pcm side or the pump tank side

This has saved me from dropping quite a few tanks finding out the pump is fine and the issue is with the fuse/relay/wiring or ignitions switch/ computer

Let us know what you find

Also check your battery connections check the ground wires make sure they are all hooked up especially the engine /
Frame battery ground connections since you had the engine out
 






Adam Robert

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ST Fuel Wiring.jpg

Update from this morning's test. I was able to get proper ground from the inertia plug. When I put the key in the ON position, I did get power to the switch, but only for maybe 1/2 to 1 second, then it was gone. I believe this needs to be a constant flow when the key is in on or run. I can't for the life of me understand why it would only be there for a moment like that.

I have included a screen shot of the wiring diagram I am working with. I have added quick notes in red to explain where these wires lead to next. Electrical is easily my weakest strength with auto repair, so making some of this make sense for me it likely a bit more difficult than others. I hope this helps someone else to explain it to me.
 






410Fortune

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It only primes the pump when you turn the key to run
When the engine starts the pcm will enable the fuel pump full time
 






Adam Robert

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It only primes the pump when you turn the key to run
When the engine starts the pcm will enable the fuel pump full time
There is only one source of power to the fuel pump and it runs directly through the inertia switch. What could be telling the PCM to shut that power off? Could it be an issue with the evap canister or vent? Maybe an issue with the O2 sensors? The DK GRN/YEL wire also goes to the PCM fuel pump monitoring system, if the pump was bad or some other issue, would the monitor stop sending power to the fuel pump relay, which would shut the power off?
Screen Shot 2022-05-11 at 10.04.21 AM.png
 






Fix4Dirt

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afaik when you primenit only pressurizes for about a second just to build enough pressure just to begin syarting, at which point then pump then shuts off and the system is pressurized and ready to start. i believe the module knows that the vehicle isnt actively running, so then it only primes the system. if its runninng, then the pump is pumping :D this is my understanding ag least!
 






Adam Robert

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afaik when you primenit only pressurizes for about a second just to build enough pressure just to begin syarting, at which point then pump then shuts off and the system is pressurized and ready to start. i believe the module knows that the vehicle isnt actively running, so then it only primes the system. if its runninng, then the pump is pumping :D this is my understanding ag least!

Well.... I just tested the very same concept on my other ST and it acted the same way, so it appears you are right. Moreover, I think I have proven that the pump is indeed getting power, but is not running. This was no doubt an unexpected expense, but it appears I will need to bite the bullet on a new pump.

As one final test, are either of you two who are responding able to tell me how to safely do that 12V jump test?
 






Fix4Dirt

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im not too sure. however, if you can find which pins on the relay get the 12v, maybe you can give it power. or 410, would just giving it generic 12v not from the relay work? i dont see why not, but i feel like the relay is afer, but what do you think?
 






Adam Robert

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im not too sure. however, if you can find which pins on the relay get the 12v, maybe you can give it power. or 410, would just giving it generic 12v not from the relay work? i dont see why not, but i feel like the relay is afer, but what do you think?
I'm really not sure. With as inexperienced and not knowledgeable as I am with electricity, I am super unsure about hooking power up directly to anything and particularly so when its near fuel. I plan on dropping the tank after work and perhaps the final test I could do would be with the safety of a test light. I can make sure there is power and ground at the pump connector and this should ensure that it is a bad pump (or not).
 






Fix4Dirt

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alright! imo, i wouldnt run the pump when its dry though, as the fuel lubricates the pump to keep temps down. aso, do you plan to repace the whole sender or just the pump? at 320k i did the whole sender, but prior just the pump and the sock lookin thing at the bottom.
 






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Beware sending 12v straight to the pump might make a weak pump seem normal. I believe the PCM sends a lower voltage. The 12v might just wake it up.

Fuel pump failure is much more likely than wiring failure.
 






Fix4Dirt

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in that case then can one send power from the relay straight to the pump to rule out any wiring failure?
 






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in that case then can one send power from the relay straight to the pump to rule out any wiring failure?
Applying 12v from the battery to the fuel pump power socket in relay board would do it. If nothing heard then run 12v battery jumper to the fuel pump + in connector in frame rail. Assuming ground is good the pump should run
 



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Fix4Dirt

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Applying 12v from the battery to the fuel pump power socket in relay board would do it. If nothing heard then run 12v battery jumper to the fuel pump + in connector in frame rail. Assuming ground is good the pump should run
thanks! good to know! hopefully also OP can measure pressure too!
 






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