Ford Bronco One of the original SUVs, offered in both a full size Bronco, or the more compact Bronco II.

96 Bronco fuel issue

  #1  
Old 03-02-2019, 07:30 PM
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Default 96 Bronco fuel issue

Ok. So I just got a 96 Bronco with a bad fuel pump. I dropped the tank, pulled the pump, confirmed it was bad. It sucked up a deteriorated sock and burned the pump up.
I replaced the fuel filter. Added gas. When I turned the key the pump doesnít do itís 2 second prime. I checked all the fuses and tested the relays for the PCM and fuel pump. All good. I jumped the fuel relay and the pump runs. So everything from the relay back is good. With the key on I have power to the light blue/orange, red, and yellow wires but not the dark green/yellow wire. So at this point I suspect itís the computer. I pulled it out and found a good amount of Rust on the case. The wiring connection is good and clean. I replaced the PCM. And still not getting power to the pump. What am I missing? Iíve checked every ground I can find visually and with a power probe and ohm meter. Any help is appreciated!
 
  #2  
Old 03-02-2019, 08:00 PM
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There is a power relay within the PCM that has to work before anything else the PCM controls can work. The PCM via the power relay does control the grounding of the fuel pump relay pick circuit.
You said you checked all the fuses, the ones in the Power Distribution Panel under the hood also? Any corrosion on the PCM plugs? Pins look OK?
Can we inquire where you obtained the replacement PCM?
A reminder, just looking at ground connections or checking with an ohmmeter is not very reliable. The connections have to be removed , cleaned and reinstalled to be done correctly. If not careful, when using a power probe with computer circuits sometimes can get you into trouble. Even test lights and computers don't like one another very much. A lot of PCM circuits work on millivolts and are extremely sensitive to excess voltages.
 
  #3  
Old 03-02-2019, 08:56 PM
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I checked the fuses under the hood. All good. I even pulled up the panel and back probed to check it out. As far as I can tell the pcm relay is powering up. I ordered a refurbished pcm from fs1inc.com. All the pcm pins looked very good, no debris or corrosion.I didnít use the power probe to apply power anywhere on the pcm wiring. And the wiring diagram I have shows that the pcm controls the power to the fuel pump not the ground.
as for the grounds, I checked for resistance from the ground spots I could find. High resistance equals bad ground. Didnít see that at any ground I checked.
 
  #4  
Old 03-03-2019, 03:42 AM
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Something to keep in mind.,
One single strand of wire will read 0 ohms and yet not carry enough current to operate a circuit. If you want to use a meter to check connections you need to load the circuit and do voltage drop tests.
 
  #5  
Old 03-03-2019, 04:15 PM
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I did some voltage drop tests today. Thanks for the advice.
Still canít find an issue. But, as I was hiding from the cold and wind in the truck, I thought to put the trans in neutral and turn the key. So I did... and I heard the pump kick on for about two seconds. Iím guessing that itís a park/neutral safety switch?
Any advice on testing it?
 
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