After installing a brand-new OEM pump the fuel gauge flucuates?

Tiny
RALPHP1254
  • MEMBER
  • 2003 OLDSMOBILE ALERO
  • 3.4L
  • V6
  • 2WD
  • AUTOMATIC
  • 192,195 MILES
Ever since I replaced my original pump with a brand-new OEM pump, my fuel gauge has been moving up and down sitting still and going down the road. I already checked the float arm, and everything appears to be fine. Not getting hung up anywhere.
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Friday, January 31st, 2025 AT 2:37 PM

20 Replies

Tiny
KEN L
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Thanks for the video, it helps. This happens when the small ground wire going to the fuel tank sender is not connected to ground. Can you confirm? Also, when you say the OEM pump was it the complete pump module with fuel level sender?
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Saturday, February 1st, 2025 AT 11:43 AM
Tiny
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How would I check the ground? It seems it’s a bad connection as it stays normal during the first few minutes of the drive and then it dances like crazy. Yes, it’s a complete assembly. Brand new Delco unit.
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Saturday, February 1st, 2025 AT 12:46 PM
Tiny
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I pulled my seat, and I saw these bunch load of wires. Which one would we need to check?
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Saturday, February 1st, 2025 AT 1:02 PM
Tiny
KEN L
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Did the new unit come with the sender as well? It should be blk or blk/wht wire. Also, there might be a ground wire at the fuel pump module as well, black signal wire.
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Sunday, February 2nd, 2025 AT 8:50 AM
Tiny
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Yes it did. It was a complete assembly. And what I found out is the back seat is causing it to go out of control. When it’s out, it stays fine. I wonder if a ground wire in that harness is being pinched.
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Sunday, February 2nd, 2025 AT 9:16 AM
Tiny
KEN L
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A pinched wire can cause this issue yes, also recheck the ground wires.
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+1
Sunday, February 2nd, 2025 AT 11:01 AM
Tiny
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Ground wires look good. No burns or splits on them.
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Sunday, February 2nd, 2025 AT 12:05 PM
Tiny
KEN L
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I am wondering if the fuel tank is not grounded. Did it have a small ground wire when you removed it? Can you rig a ground wire to the tank and recheck it?
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Monday, February 3rd, 2025 AT 8:06 AM
Tiny
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From what I can tell, there is only a small black/white ground wire in the tank harness. Should I check that one?
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Monday, February 3rd, 2025 AT 8:08 AM
Tiny
KEN L
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Yes, the sender has a ground that goes to the PCM, I would check this wire, I have a guide to help, and I included the fuel sender wiring diagrams for clarification.

https://www.2carpros.com/articles/how-to-check-wiring

Check out the images (below). Please let us know what happens.
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Tuesday, February 4th, 2025 AT 8:42 AM
Tiny
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It’s been a while, and I can confidently confirm the black ground is on the pump. It’s hooked on tight. With the car not even running, it fluctuates even with the harness unplugged from the car.
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Sunday, June 8th, 2025 AT 1:33 PM
Tiny
KEN L
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If the grounds and the wiring looks okay then I would say you got a defective fuel pump, I would swap it out, sorry.
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Sunday, June 8th, 2025 AT 2:03 PM
Tiny
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I actually have already replaced it after that last one you sent on the ground wire. And it still does the same even with a brand new OEM fuel pump. The only thing I can think of is a bad spot in the tank harness or bad spot in the harness in the car. Pump is brand new still. You can also unplug the whole thing, and it still does it too.
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Sunday, June 8th, 2025 AT 2:09 PM
Tiny
KEN L
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Yep, that would be an open wire, Let double check the blk/wht and purple wire from the sender to the PCM, here is the other wiring diagram you need besides the diagrams above, use the guide above as well. Pleas let me know how it goes. Check out the images (below).
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Sunday, June 8th, 2025 AT 2:36 PM
Tiny
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The wires under the car or the ones on the plug to the PCM?
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Sunday, June 8th, 2025 AT 2:54 PM
Tiny
KEN L
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Yes, from the fuel sender to the PCM.
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Sunday, June 8th, 2025 AT 3:03 PM
Tiny
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Ok. I’ll unplug the harness and check it out and report back what I find.
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Sunday, June 8th, 2025 AT 3:08 PM
Tiny
KEN L
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Thank you, have a good week!
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Monday, June 9th, 2025 AT 8:53 AM
Tiny
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Yes. It is indeed the harness that runs to the fuel tank and hooks up to the body harness. But instead of repairing it, I’m going a get known good harness since mine has been spliced so many times it doesn’t have any slack in it
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Saturday, June 14th, 2025 AT 12:50 PM
Tiny
KEN L
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Good call, sometimes it is best to do it that way. Let me know how it goes.
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Sunday, June 15th, 2025 AT 10:14 AM

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