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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1667
Experience:  GM Grand Master Technician 2007. 14 year experience.
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I have a 96 GMC 3500HD dump truck with a 7.4L gas engine

Customer Question

I have a 96 GMC 3500HD dump truck with a 7.4L gas engine that has gas guage problems. I understand the principals and components of the dual system tanks. When the truck is first started the gas gauge needle will move to about 3/4 empty, and wiggle for about 10 seconds. After that the needle falls below empty and does not come back on until the engine is shut off, then the cycle starts again. I've checked all the grounds and connections and all seems tight and secure. Where should I look now to get my fuel gauge working correctly again.
JA: Has the vehicle turned into a gas hog? And how does it start -- same as usual?
Customer: starts normally, and doesn't seem to be a gas hog. although its hard to tell
JA: What is the model of your '1500 GMC?
Customer: 1996 3500HD 7.4L Gas
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: yes, checked fuses, grounds and connections
JA: Anything else you think the mechanic should know?
Customer: not that I'm aware of
Submitted: 3 months ago.
Category: GMC
Expert:  Kevin Bourcier replied 3 months ago.

hello . I can assist you with this . Your truck has a single tank ?

Customer: replied 3 months ago.
No, dual tanks
Customer: replied 3 months ago.
the main tank, which feeds the FI and is located inside the left frame rail. the auxiliary tank is located behind the rear axle and feeds the main tank or is suppose to when its working correctly.
Expert:  Kevin Bourcier replied 3 months ago.

the fuel gauge operates that way regardless of which tank you are using ?

Customer: replied 3 months ago.
The fuel gauge is only connected to the fuel pump balance module. The auxiliary tank feeds the main tank when the fuel level in the main tank falls.
There is no switch which allows me to choose which tank I use.
Expert:  Kevin Bourcier replied 3 months ago.

okay . Hmm . I need to double check the schematic . the one I was shown shows a manual tank selector switch .