(ECU was replaced recently with a reman and ran like new)

I knew the JY fuel pump I put in when I got it was on its way out and I thought it finally quit in the driveway the day after I drove it far since the next day it was crank with no start but I could still hear it barely running past the 30 sec prime time, I bought another lower mileage oem motorcraft to put in and it doesn't turn on, I had old short bed fuel pumps that were cheap no brand and motorcraft that I tested on the connector and the other motorcraft doesn't turn on but the no brand one does the same as the pump in the truck (seems to make a prime noise and then has a weak buzz that stays on with key)

I read into it and online is saying a bad ECU causes this and I did replace my bad original ecu with a newer remanufactured one from rockauto and I'm ready to give up on the truck after the amount of work and money I put into it right when it's running like new something else goes 😡

any help appreciated I can still return the rockauto ecu if that's the problem but it was their last in stock so I'm screwed if that's the fuel pump problem (everything else works like new)

 

1993 4.0l?

Computer primes for 2 seconds only, each time key is turned from off to on

If its a 1993 then its OBD1 so it will have a bypass you can use to test fuel pump relay or computer issue

Next to the engine bay fuse box will be the OBD1 test connector, may have a cover that says EEC on it

Looks like this: https://www.therangerstation.com/tec...v_testing2.gif
Fuel pump slot is labelled in drawing

If that slot is GROUNDED it will bypass computers control and close the fuel pump relay, but only with Key ON

So use a jumper wire in that slot and to battery negative or a good ground point
Turn key on
You should now have 12volts at the fuel pump's wire at the tank connector, should be the pink/black wire
Fuel pump also has a Black ground wire on same connector, it needs to be a good ground or pump will barely run

1993 engine fuse box diagram below
You can pull out fuel pump relay and check for corrossion
Also fuel pump fuse

If you pull out the jumper on OBD1 connector, key still ON, you should hear fuel pump relay "click" off, put jumper back and it should "click" on again

There is an inertia switch in the cab, passenger side footwell on firewall, looks like this: https://static.cargurus.com/images/s...1600x1200.jpeg
You can see the green/yellow wire from the relay and the Pink/black wire OUT to pump in the picture
This is an ON/OFF switch, so unless its highly corroded it can't just reduce voltage at pump

 

Yes 1993 4.0L, I tried the jumper wire to the battery ground and a clean body ground and nothing happened when I turned the key on and while it was on I tried taking the wire on and off to hear a click and nothing... so I pulled the fuel pump fuse and relay and they looked like they're original but they arent blown or corroded. I found the inertia switch and tried pressing it but it was already pressed in so does this mean the reman computer works but some fuel pump circuit decided to quit?

thanks for the help so far

 

Does the CEL(check engine light) come on with key on?
If so skip the next bit
If not then test PCM relay

EEC/PCM relay powers the Fuel Pump relay with key on
If you have a helper have them turn on the key while your finger is on the PCM relay, you should feel it click closed, if not swap it and retest

If you don't have a helper disconnect one battery cable and turn key on, connect cable with finger on PCM relay



PCM relay powers the "ECU"/PCM, along with fuel pump relay, all the injectors, EVAP system, and MAF sensor
PCM turns on the CEL when it has booted up
It also has a fuse in engine fuse box you should check

 

Yes it definitely clicks and the CEL is on, I had a helper turn the key and the fuel pump relay and the PCM power relay click so I took the fuel pump relay out to make sure the pcm relay was the one clicking and it was so right now I'm working on taking the new computer out to try my old one to see if the fuel pump can prime and start the truck because the old computer would always start the truck it just had stalling issues so anyways I'm starting to think maybe it's something else causing the computer to burn up since it ran and drove great when it was first put in and then after it cooled down and got messed up? I'm not sure I just want to do the computer swap test while there's daylight and if you approve of me returning the new computer to get another working ford one or reman then I will return it

​​​​UPDATE: I put my old computer back in just now and nothing changed, just clicks the two relays and cranks but no pump so it's not computer related apparently

EDIT: I also noticed my ignition switch is a little sloppy than usual and its hard to take the key out I have to wiggle the metal wing nut looking part back and fourth while holding the key and I read an ignition switch short could cause this, what do you think?

 

Well ignition switch is under steering column above brake pedal, the key just turns a gear that slides a rod inside steering column that moves ignition switch in to one of its 4 positions
ACC OFF RUN START

Problem with ignition switch itself could maybe cause the issue, but not specifically related to just fuel pump power

You know which one is Fuel Pump relay, so pull it out
Ford used two different styles of relays, Micro and Mini

Micro seen here: https://www.gtsparkplugs.com/images/...lay-wiring.jpg

Mini seen here: https://www.gtsparkplugs.com/images/...iring-840x.jpg

Pin/slot layouts are different but pin/slot numbering was the same

30 and 87 are the Load, when these tow slot are connected the Device gets power/12volts in this case

85 and 86 are the coil, when one is 12v and the other a ground, relay activates and 30 and 87 are connected

87A is not used in this application so may or may not be there

With Fuel pump relay out use a Jumper wire to connect 30 and 87, fuel pump should now have 12volts, key on or off doesn't matter
If no 12v then wire to fuel pump is broken


If you are wondering about the odd numbering, its from early days in the first vehicles to use Relays In Germany, these relays were made by Bosch
DIN is an automotive engineer group in Germany, you may have heard of DIN and double DIN Radio sizes, this is from that group, as are the relays numbering standard
Why they picked these number was because of circuit drawings/schematics, the numbers were unused at the time, well 30 was used but as Voltage pin/slot which is what it is on relays

 

Thats interesting about the numbers I'm into car audio so Ive heard the double and single din stuff, Yes it's the mini relay. I was excited to try this but today I connected the jumper wire to 30 and 87 with key off and nothing happens

 

Then wire from relay to pump is bad


With jumper in place, use a volt meter or test light at inertia switch first to see if you have 12volts there, if so then wire from inertia switch to pump is bad, usually a pink/black wire

If no 12v at inertia switch then green/yellow wire from relay to inertia switch is bad

 

Thanks, hate to repeat myself but again what I don't understand is that the wiring is able to power certain pumps with a prime and low voltage but not ones that fit in that tank to start the truck. that sucks I don't know how it was working and the wiring quit overnight.

 

Maybe the pumps that don't work have a diode in them so only work with + and - connected a certain way, some do so they turn the correct direction to pump fuel OUT, not suck fuel in, lol

Take non-working pump to battery and test it
Reverse polarity on the 2 wires, won't hurt anything to test it that way, to see if it works one way but not the other, kinda like LED lights have a + and - and won't work if reversed

And if a wire is corroded some fuel pump need more amps than others, so if you see that big of a voltage drop, as said, then a wire is corroded
All fuel pumps are not created equal in Amp draw

 

That would make sense except for the fact the original pump out of the truck (that works) and the replacement are literally made for it and the ones that arent barely work (must be a lower draw for 4 cyl shortbed rangers etc) but ill still test the replacement pump, also theres crusty original dielectric greese on the replacement pumps connector and the harness that clips to it and that's the only voltage drop related thing I can think of but obviously that wouldn't effect it as I've seen people pack way more in things in hopes to waterproof etc. also you're saying the connector off the pump goes directly to the inertia switch and from there to the fuse box? if you know where it leads to and what color wiring does what, if I get desperate enough I might hardwire an auxiliary switch to the positive and negative going to the cab direct (fused) 12v from the battery without any relays or computer but I probably wont because that's sketchy unless you could think of another work around to skip the factory wiring (It doesn't matter if it's pretty I just need it to run and be reliable and not burn down and not continue to pay shops more than the truck is worth)

EDIT: Ebay sells the connector with wires on it just cut halfway that came off another ranger for dirt cheap so I would have a secure connection to the pump atleast without cutting mine also the reason Im not testing the factory wiring like you said to is because my multimeter broke and I'm trying not to completely rage working with electrical wiring thinking of semi temporary work arounds

 

Yes the pink/black wire at the tank is from inertia switch, fuel pump power
Black wire is fuel pump ground at the tank

Yellow/white wire is for sender, fuel gauge, 5volts
Black/white or black/yellow is sender ground


Heads up on "new" parts
New used to mean "tested and working"
New now means "YOU TEST IT, and we will replace it if it doesn't work"

In a "good ol' days" parts were expensive to make but labor was cheap, so there were Quality Control Departments, parts were test by workers before being boxed and shipped
Now, parts are cheap and labor is expensive, so no more Quality Control, we get cheaper parts cost but have to test it ourselves and the parts maker will exchange it if it doesn't work

"New" means UNTESTED, so grain of salt

 

Right I agree, that's why I only replace parts I want to work and be reliable with ones that are from a junkyard or a jy online dealer even though its controversial and I get it but I trust motorcraft back then instead of pure china with zero quality control. anyways I'll be out of town for a couple days thanks so much for your help, when I'm back working on the truck I'll either update you here or start a new post

 

alright heres the update; I tested everything you said to check and more reading other people's posts having this issue and everything was getting proper voltage I even checked the fuse box terminals at relays. it used to prime 8 volts to the pump harness so I unplugged the inertia switch and the switch itself looked pretty moist as it gets really humid in the cab after it rains for a while for some reason so I tested the connector but I didn't know if it would be bad for the computer turning the key while its unplugged so I put it back and the jumper wire actually worked this time with leaving the pump on (the plug on inertia switch looked brand new, no melting or corrosion) so after it got the 2 sec of 12 point something volts on a wrong size pump I put it on the new pump in tank and nothing... I tried three others and only two of three rando worked properly this time so I thought it was picky untill I hotwired them directly to the battery to see if they work and come to find out the only ones that worked on the trucks wiring were really the only working ones to my surprise, the thing I needed to ask was that after it does a 12v prime it drops down to 6 point something volts? is this normal? it does a strong prime and then quickly cuts off after the 2 seconds (no weird low voltage buzz this time even tho its still getting 6v) so my best confused guess why it works is that the pump I bought never worked out the box and that current going to a seized pump messed with it so after using the jumper on a different pump and unplugging and plugging the inertia switch in it works? not sure I'm just very happy it is, because I could technically drive it today without a fuel level but I'm going to wait for the proper pump to come in and return the broken one obviously

I'll attach pictures just because I wanted you to get a visual on it

Heres what the pump gets with everything put back and from the key prime

you never mentioned pink and green, only pink and black so I thought id show mine

as you can see the button is pressed in

heres the three prong two wire connector

 

Yes, it should have 12v for just 2 seconds and then drop to 5-8volt, thats the fuel pump relay activating and deactivating
The 5-8volts has no AMPS just volts, its from the computers Monitor Circuit
Computer controls the fuel pump relay so it monitors if fuel pump gets 12volts with Fuel Pump relay on, if not it will set a code