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2001 GMC Flat bed 6500 Gas

Rick Ortega

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Hi i have a 2001 GMC flat bed truck 6500 with duel tanks ,my right works my left does not work . i change the fuel pump, fuel relay, and a square box above the relay still does not transfur over fuel
 

Jaryd

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there have been a couple different threads pop up recently with this kind of problem. Might can do a search and find them and see if there is anything in them that can help you out.

@THEFERMANATOR has helped out with a couple different duel tank problems
 

THEFERMANATOR

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I'm not familiar at all with the 6500 chassis and my manual only goes up to the 3500hd. Most of the time on the ones I've dealt with, the left/drivers side tank is the main, and the right side is the transfer tank. Is this a dual tank system with a switching valve, or is it a dual tank transfer system? Does it have 1 fuel gauge that shows the level in both tanks at the same time, or does it read each tank independently? Just trying to figure out what system you're working with.
 

THEFERMANATOR

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I just looked on rockauto and they spec the high pressure pump for the left side tank to run the engine, and the right side tank uses a low pressure transfer pump to move fuel over from the right to the left. I'm guessing both senders are wired into the PCM, and it controls the engine fuel pump to run the engine, the transfer pump to move fuel over, and then outputs the signal for the fuel gauge as this is how GM does it on all there other trucks in 01 with an 0411 PCM.
 

Rick Ortega

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I'm not familiar at all with the 6500 chassis and my manual only goes up to the 3500hd. Most of the time on the ones I've dealt with, the left/drivers side tank is the main, and the right side is the transfer tank. Is this a dual tank system with a switching valve, or is it a dual tank transfer system? Does it have 1 fuel gauge that shows the level in both tanks at the same time, or does it read each tank independently? Just trying to figure out what system you're working with.
I'm not familiar at all with the 6500 chassis and my manual only goes up to the 3500hd. Most of the time on the ones I've dealt with, the left/drivers side tank is the main, and the right side is the transfer tank. Is this a dual tank system with a switching valve, or is it a dual tank transfer system? Does it have 1 fuel gauge that shows the level in both tanks at the same time, or does it read each tank independently? Just trying to figure out what system you're working with.
Yes thanks for your reply: I found out thru GM that the main tanks sending unit has to be working so that it can send a signal to the other tank to Transfer fuel over. Thanks
 

THEFERMANATOR

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Yes thanks for your reply: I found out thru GM that the main tanks sending unit has to be working so that it can send a signal to the other tank to Transfer fuel over. Thanks
BOTH senders MUST work and send fuel level signals to the PCM. It monitors the main tank, as it drops, it turns on the transfer pump to move fuel over from the right tank to the left, and if it doesn't see the levels change in each tank accordingly, it assumes there is a problem, and disables the whole system and defaults the fuel gauge to empty.
 

Rick Ortega

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BOTH senders MUST work and send fuel level signals to the PCM. It monitors the main tank, as it drops, it turns on the transfer pump to move fuel over from the right tank to the left, and if it doesn't see the levels change in each tank accordingly, it assumes there is a problem, and disables the whole system and defaults the fuel gauge to empty.
thank you, for your help.
 
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