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HELP! 94 Ford Explorer won't start, no fuel pump sound, code 543

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Old 09-18-2011, 04:17 PM   #1
CTroxtell
High Point Area, NC
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HELP! 94 Ford Explorer won't start, no fuel pump sound, code 543

Well I was coming home from work last night and when I turned the corner my engine died. I turned the key off and back on and couldn't hear the fuel pump so I went and bought a new fuel pump and installed it. Needless to say it still won't start, I pulled the codes and I am getting a 543 Fuel Pump Circuit open - Battery to PCM.
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Old 09-18-2011, 05:03 PM   #2
MrShorty
Spanish Fork, UT
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Can I assume it is a KOEO code and not just a CM code?

Just reading the code description, KOEO 543 indicates a break in the fuel pump circuit between the battery and the point where the fuel pump monitor circuit branches off of the fuel pump circuit to the PCM (If memory serves, it goes to pin 8, but you'll want to verify that with a wiring diagram). Diagnostic steps: I'd start by getting a wiring diagram and a multimeter. Start at the battery and trace the fuel pump circuit until you find the break in the circuit.




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Old 09-18-2011, 06:06 PM   #3
CTroxtell
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Yes it is a KOEO code. The truck won't run because of whatever it is. Pin 87 on the relay is the only one that has battery voltage. 87 is the left pin I think, if I put voltage to the bottom pin 86 (bottom pin) pump runs but not sure how safe that is .
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Old 09-18-2011, 07:14 PM   #4
jt thomas
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check the inertia ss

every explorer i have had has done this at one time or another. usually hte inertia safety switch is in the passenger floorboard just below the dash but behind the carpet. usually once it goes bad thats it pump wont work and it just turns over. put another one in and it will most likely solve your problem. 75.00 from ford if advance auto or autozone can get them from doorman probably half that. hope this helps you out.
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Old 09-18-2011, 10:35 PM   #5
MrShorty
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if I put voltage to the bottom pin 86 (bottom pin) pump runs but not sure how safe that is .
I don't know which pin number goes to which wire. I'm guessing this means that pin 86 is for the green/yellow wire that goes to the pump. This also suggests that the pump itself and all of the wiring between the relay and the pump are good.

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Pin 87 on the relay is the only one that has battery voltage. 87 is the left pin I think,
Is pin 87 for the black/yellow wire that comes from the battery/fuse or is it for the red wire coming from the EEC relay? With the key on, there should be at least two leads at the fuel pump relay that have 12 V. If you've only got one, then we identify which one doesn't have power and we will know which way to go next.




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Old 09-19-2011, 08:03 AM   #6
CTroxtell
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Originally Posted by MrShorty View Post
Is pin 87 for the black/yellow wire that comes from the battery/fuse or is it for the red wire coming from the EEC relay? With the key on, there should be at least two leads at the fuel pump relay that have 12 V. If you've only got one, then we identify which one doesn't have power and we will know which way to go next.
Okay, the red wire has voltage. The black/yellow wire has nothing.
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Old 09-19-2011, 09:03 AM   #7
MrShorty
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So now you work back from the relay through the fuse to the battery until you find the break in the circuit.
As dumb as it sounds, have you checked the fuse to see if it has blown?




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Old 09-19-2011, 09:34 AM   #8
CTroxtell
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What fuse is associated with this?

EDIT: Well I found the bad 20 amp fuse, broke out the multimeter and started checking all the fuses for continuity . I never seen anything anywhere even in the books that mentioned a fuse. Someone should really list that kind of information. For anyone in the future it is the mini fuses in the power distribution box, the one of the bottom left. Well I got a new fuel pump out of this whole ordeal.

EDIT 2: I think the fuel pump was shorting out because the insulator on both of the wires leading to the fuel pump inside the tank had some how moved and allowed the wires to touch. Well now I just got to try to check my catalytic converter, I think it is stopped up because I have premature detonation in the cylinders I believe because of the back pressure.

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Old 09-20-2011, 05:17 PM   #9
pmcdon
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I am having a wiring short problem with my 97 explorer. The car died on my wife while driving it so she had it towed back. I checked the fuel pump and couldn't hear it running. So i swapped the relay with a known good one in the PCM and still nothing. Checked the fuse and sure enough, blown. So I swapped it with another one in the PCM and as soon and it made contact it arced. So I pulled the relay replaced the fuse and then put the relay back in and tried to start but nothing. Checked the fuse, and blown again. I traced the wireing haness from the PCM to the inertia switch back throught the firewall and then under the truck along the frame. couldn't find any evidence of wear or a short. I replaced it with my last fuse and it held out and the truck started just fine but started running a little rough. About a week has gone by and today it blew the fuse again. I tried swapping i out and it blew instantly. I climbed underneath and wiggled the wire along the rail and replaced the fuse and it started fine. Drove 3 miles and as I'm pulling into the driveway, it blew the fuse again. This time the first fuse replacement got it started again, but I tried to jiggle the wire along the frame to make it trip and it wouldn't.

I'm hoping that there is a common short in the wireing system for the fuel pump. Any help would be much appreciated as this is the only vehicle to transport my kids to school in.

Thank you
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