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Hi, I am typing this while staring at this bronco that has stumped me. I just acquired it from a family member and it has been sitting for a while. While trying to get the thing started it wouldn’t turn over and I soon realized I didn’t hear the pump priming. I checked the relay - has power, Inertia switch - working, and the plug itself to the pump has power. We pulled the old pump out and replaced with a new one that kicked on when it was hard wired to a battery. My question is that the plug has power and the pump works but when it’s plugged into it neither seem to work at all and i’m just stumped. If anyone has a clue that would be great. Thanks in advance! photo of our work so far
Chris, i'm not the expert and hopefully the experts will chime in! But since i have had similar issues-
What year is this? makes a difference 84-85, 86-88 and 89-90
You stated you don't hear the initial cycle up 2 second fuel prime up. I found that in my 86 that the only pump you really can hear is the Hpump (hi pres pump on rail) it's wierd that you have power at the low pres pump but plugged in you say not working however the relay does work.
I think you should check the Hpump and it's connections (that is if you have 86-88) 86-88 There is a plug under the apron under the master cyclinder that has 1 hot wire in and 2 hot wires out - splits the power to both pumps (that plug gets greened out)
You might have to learn how to ground out pin#6 on the ODB1 so you can turn key and fuel pumps will stay on so you can wiggle wires etc etc.
Otherwise, here is some more info about troubleshooting that i found and copied long ago:
Yellow/white is voltage from the fuel gauge. The sender in the tank varies the resistance on this wire.
Once you have your jumper connected & the key on see if you have 12 volts at the inertia switch.
Heres how it's wired:
Pump relay to inertia switch on orange/light blue
Inertia switch to connector C160 on pink/black
Connector C160 to C161 & on to the pumps on black/pink.
Solid black is pump grounds
Solid orange is the fuel gauge ground.
BTW, the pump circuit only stays hot for 2 seconds each time you turn the key. Kinda hard to test in only 2 seconds. Thats why you need to see the link and run the jumper.
When you turn the ignition to Run, the fuel pumps should run for about 2 seconds and then shut off because no ignition reference pulses will be found because the engine is not running or cranking.
With the ignition key in Run, at the Fuel Pump Relay you should measure 12 volts on the small Red wire. This 12 volts comes from the ECC Power Relay.
On the Large Yellow wire you should measure 12 volts at all times. It comes from a fusible link that is attached to the starter solenoid lug on the battery side.
The EEC energizes the Fuel Pump Relay by grounding the small Tan/Light Green wire. When the relay energizes, 12 volts from the Large Yellow wire passes thru the relay to the Large Brown wire and then 12 volts is applied to the fuel pumps.
So if you ground the Tan/Light Green wire and start the engine and it runs, I'd say the computer is bad.
If you triggered the FP relay, and didn't hear the in tank pump run, then the problem is between the in line pump, and the in tank pump. Broken wire, crappy connection, or bad pump.
If your in-tank fuel pump is not running:
To rule that in or out, with the key ON/RUN jumper the DTC as you did before, and with a test light check for power at the in tank fuel pump. If you have power there, then your pump will need to be replaced. If you don't have power there, then you'll have to track back to the inertia switch and in between, to find a broken wire or bad connection.
Got some other input from the old heads at work and they think it could literally just be a bad ground, it’s an 88 if that helps. I appreciate the help and i’ll take a look at it when I get home from work.
When we were testing we had a light tester and it was in fact no light, had no idea that the ground was supposed to light up so good to know. I appreciate the help!
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