Fuel gauge issue?

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.

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
48,571 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

BULLITT1939

MEMBER
35 POSTS

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

KEN L

MASTER CERTIFIED MECHANIC
48,571 POSTS

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

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