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Does anyone know exactly how the MPG is calculated, is it metered through the injection as used, or "Old school" (engine vaccum and or fuel level remaining) or..........

I am getting a 91 gallon bed mounted fuel cell/toolbox, total fuel 125 gal that used a ballcheck tube as perpetual feed to the main tank till drained.

Anyone else done this and will the onboard computer get as confused as I am?????



07 2500HD LBZ, LT3, Hypertech III
 

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The onboard wont recognize the new tank. It'll just show the original tank as Full because it will be getting refilled automatically while driving.
It wont account for the new 125 gallons under miles remaining or anything.
I think it calculates gallons used divided by miles driven...
 

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Talked with my dealer tech about this same addition. He informed me that the setup your getting will cause the truck to have DTC come up and the fuel gauge will stop working when the ECL comes on. I am having a 45 gal. Box/Tank combo installed this Wednesday. It is made by American Tank Co. and it works as a seperate fuel tank with its own float. The OEM gauge will read each tank and the tanks are switched by a dash mounted switch. When a auxillary tank is used as a transfer supply the ECM reads that no fuel is being used and it throws a DTC.
The tank combo I'm having installed runs around $1800 installed.
 

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You will have no problems. My 91 gal combo is gravity fed and been like that for 200,000 miles. The fuel gauge will go to empty (when you leave your valve open on the aux tank)and the low fuel light will come on because the truck thinks the sender is stuck. But once you run the aux tank out the gauge will return to the full mark and show the level in the oem tank.
 
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