How do Yukon XL dual fuel tanks work?

[56napco]

So my '02 Yukon XL 2500 is the first truck I've had with these dual tanks. I would like to know how they work. Does the rear pump into the front tank when the front reaches a certain level or does the rear pump into the front continuously?

[txab]

On dual tank applications, The secondary fuel pump is located in the secondary fuel tank. The secondary fuel pump is powered by a secondary fuel pump relay when the fuel level drops below a predetermined value. Fuel is transferred from the secondary fuel tank to the primary fuel tank in order to ensure all of the usable fuel volume is available to the primary fuel pump. The secondary fuel pump relay supply voltage is received from the primary fuel pump relay when the primary fuel pump is energized.

[Morgan1986]

would suck if something broke down . I know the older fords it was just a switch and it would switch over to the other tank.

[MikeNH]

would suck if something broke down . I know the older fords it was just a switch and it would switch over to the other tank.

 

 

The F-150 I had in highschool was like that- 42 gallons I think! Thank god it was like $1/gallon back then.

[56napco]

alright, thanks. Just made me wonder when I put on over 300 miles and the lowest the guage went was 3/4 tank. My '74 pickup has separate tanks, with separate sending units, just switch between them. The new dual tank setups had me confused. Is there anyway to know what that predetermined level in the primary tank is that tells the secondary pump to kick in? The gauge never shows it's filling, so it won't go to 1/2 tank and then head back to full when the secondary pump turns on. Makes ya nervous when the gauge never seems to go below 3/4 and you don't know if the gauge is right or the secondary tank is keeping the level in the primary tank constant until it runs out.

[56napco]

Ok, back to this topic. Last week the fuel pump failed and I had the local GM dealer install a new one. Now the gauge does not read correctly and I've actually had the gauge go from 3/4 tank, to E then back to 3/4 while driving. Also, I'm convinced the gauge does not read correctly. When the gauge reads between 1/2 and 1/4 tank and it only takes 18 gallons to fill. Does anyone know the correct part number pump/sending unit for a Yukon XL with the 6.0 and dual tanks?

[chipjumper]

Sorry to wake up this sleeping bear but I just had to:

 

Here is a link to a thread that has photos of the GM parts manual that shows the part numbers. Of course these could be superceded by now but they will get you in the correct direction.