Fuel pump fault
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Laughing Gas
Joined: Jul 2023
Posts: 991
Likes: 317
Fuel pump fault
94 F150 (specs under sig) Out of the blue when I went to go start my truck it would fire up and then immediately fall flat on its face and then snap right out of it so today I checked for codes and got code 543 on the KOEO test. According to my book it's for the fuel pump secondary circuit but I was not able to find much an explanation online. Not sure if it's related or not but also had some surging issues when I started the truck this morning but as soon as I bumped the throttle it came out of it. Truck also feels like it's slightly down on power and the only things I have replaced recently are the MLPS and TFI module. I am unsure where to start but if someone could point me in the right direction that would be great. I will add some short vids down below here shortly if anyone wishes to see what I mean about the falling on its face thing or surging. Thanks for your help in advance.
I apologize about the inconvenience but I will have to upload vids later. For some reason my phone is not letting me so I will try on my computer in awhile.
I apologize about the inconvenience but I will have to upload vids later. For some reason my phone is not letting me so I will try on my computer in awhile.
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Laughing Gas
Joined: Jul 2023
Posts: 991
Likes: 317
It will not let me upload a video for some reason but I think I'm on the right track. If I'm understanding correctly this code comes up when there is a signal issue between the engine and PCM or fuel pump and PCM which means I probably have a broken wire or a corroded connection somewhere. Truck now seems to be running fine but when I was running the KOEO test it was not kicking the fuel pump on and immediately brought up the 543 code but I unplugged it all and then tried the test again and it worked fine with a 111 system pass but the 543 code would pop up after the 10 comes up once the pass code had showed.
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Laughing Gas
Joined: Jul 2023
Posts: 991
Likes: 317
I did try clearing codes but it immediately comes back. Because there is so much wiring I would have to check with little information on the problem I suppose leaving it until it becomes a major problem is my only choice.
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Laughing Gas
Joined: Jul 2023
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Does this affect both tanks or just one? I only use the front one because the back pump last time I used it was on its way to seizing up. Been trying to find a diagram on the wiring for the fuel pump but no luck so far.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
Depends on where the break in the supply voltage is.
Easy button:
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Laughing Gas
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Thanks! I will investigate deeper and report back once I get more info and see how the truck does.
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Laughing Gas
Joined: Jul 2023
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I just thought I would share something I found if anyone ever stumbles across this thread someday with the same problem.
https://stangnet.com/mustang-forums/...tc-543.477626/
I know it's for the Mustang but looks very similar and can be applied to F-Series I think.
No change with the truck except maybe a light stumble resting my foot on the throttle to maintain speed. Still starts fine so because there are so many places it could be I will probably wait until the problem becomes a major issue. I have taken a look at the wires and shaken some connectors and truck hasn't fussed once. Anyone else have or had this code present before and never have any issues? Just confusing the truck throws a fit once and now it's back to normal...for the most part on mine anyway.
https://stangnet.com/mustang-forums/...tc-543.477626/
I know it's for the Mustang but looks very similar and can be applied to F-Series I think.
No change with the truck except maybe a light stumble resting my foot on the throttle to maintain speed. Still starts fine so because there are so many places it could be I will probably wait until the problem becomes a major issue. I have taken a look at the wires and shaken some connectors and truck hasn't fussed once. Anyone else have or had this code present before and never have any issues? Just confusing the truck throws a fit once and now it's back to normal...for the most part on mine anyway.
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