Fuel gauge issue?

Tiny
BULLITT1939
  • MEMBER
  • 2008 FORD MUSTANG
  • 5.4L
  • V8
  • 2WD
  • MANUAL
  • 2,500 MILES
Have a 2008 GT500 with about 2,500 miles. I have several code issues, which I have resolved. We have brand new fuel pumps, assembly, checked sending units. Everything checks out. The car runs fine, but as soon as the car starts or turn the key gas gauge goes to empty. It also says zero miles to E. For a brief second it went to 1/2 full then E. Both sides of the tank are full as we just had to pull both sides under the rear seat! Any ideas on this fuel issue? Currently no codes right now.
Saturday, December 28th, 2024 AT 6:14 PM

7 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 POSTS
When you installed the new fuel pumps did you use OEM parts? I have seen the level sensors have an intermittent bad connection and have this problem, can I ask if you had the problem before the pump replacement? If not, then this is the first place I would look. While the pump is out turn the key on without cranking the engine over to work the sender by hand to watch the gauge readings.
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Monday, December 30th, 2024 AT 10:17 AM
Tiny
BULLITT1939
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This problem has been gone on for a while now. It was doing it with original pumps. I have replaced it with upgraded deatschwerks pumps and a new assembly since I think it might have been an issue with sending unit. Everything on the driver’s side is brand new. I also checked passenger side sending unit. It was reading correctly on a voltmeter. I drove it a few miles yesterday. It went to 1/2 tank then E. After a few minutes it went to holding right about 1/2 tank. I will order a new passenger side sending unit. That’s the only thing I haven’t changed in the tank yet.
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Monday, December 30th, 2024 AT 10:57 AM
Tiny
KEN L
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It looks like the wiring for the fuel senders goes through the SJB and then to the cluster. We should do a CAN scan to see if these components have any codes. You can get a CAN scanner (Controller Area Network) which will work on most cars from Amazon.

Here is a video to show you how:

https://youtu.be/u-4syLc-ifQ

Here are the fuel gauge wiring diagrams so you can see how the system works; it sounds like we have a connection problem or the circuit board in either the smart junction box or the cluster is bad.

Here is a guide to help you test the wiring:

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, December 31st, 2024 AT 10:58 AM
Tiny
BULLITT1939
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  • 37 POSTS
Okay, this issue is still going on. I have bought Ford originals for both the driver’s side and passenger’s side. When I turn the key sometimes it reads 1/2 a tank for a split second then goes to E immediately. Gauge cluster checks out okay. No codes given and no check engine light. Car starts and runs fine. Both sides of the tank are full. Any suggestions? I have tried a number of things, but this has me stumped.
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Thursday, February 27th, 2025 AT 7:22 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 POSTS
I see that both of the fuel level senders go through the SJB which is at the right-side kick panel, I would remove it to check the connections for corrosion which is common when the car is in wet weather. The only thing between the senders and the gauge is the wiring and the SJB. Here is the location of the SJB so you can check it out. If everything looks okay and the wiring is good, I would replace the SJB. Check out the images (below). Please let us know what happens.
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Friday, February 28th, 2025 AT 5:50 PM
Tiny
BULLITT1939
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  • 37 POSTS
Everything looked good in that SJB and all fuses were good as well. Car stays indoors and has no water issues. We checked that not long ago. Also put the scanner on it and cluster checks out fine. Only other thing we can figure out is a short/wiring issue. However, we don’t see any visible issues. Thanks for the reply.
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Friday, February 28th, 2025 AT 7:07 PM
Tiny
KEN L
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The SJB has circuit boards/processors inside of it. You can check the wiring between the level sensors and the SJB by following the post above.
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Saturday, March 1st, 2025 AT 10:38 AM

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