Jump to content

Yukon XL aux. fuel tank operation

56napco

By 56napco
in Ask A GM Technician

 Share

Recommended Posts

56napco Enthusiast

56napco

Posted
Posted

My 2002 Yukon XL has dual fuel tanks and this is the first truck I've owned with this style of tank setup. I haven't been able to find anything on how these tanks work, there isn't anything in the factory repair manuals. When does the aux. tank pump turn on? Does it continuously fill the primary tank or when the primary tank reaches a specific level? Will the gauge move when the rear pump turns on or does the gauge stay in one spot until the rear tank is empty?

txab Senior Enthusiast

txab

Posted
Posted (edited)

My 2002 Yukon XL has dual fuel tanks and this is the first truck I've owned with this style of tank setup. I haven't been able to find anything on how these tanks work, there isn't anything in the factory repair manuals. When does the aux. tank pump turn on? Does it continuously fill the primary tank or when the primary tank reaches a specific level? Will the gauge move when the rear pump turns on or does the gauge stay in one spot until the rear tank is empty?

 

 

This was answered in your other thread.

 

http://www.gm-trucks...dpost&p=1235387

 

 

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.

 

 

BTW this comes straight from the GM FSM.

Edited by txab
56napco Enthusiast

56napco

Posted
  • Author
Posted

What is the predetermined level that the primary tank needs to reach before it will turn on the secondary tank pump? Will the secondary pump fill the primary tank fast enough to show on the gauge?

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted (edited)

predetermined means what ever the engineers decided while engineering the system,,,,,

 

you have factory svc manuals ,you need to read the description and operation in the apropiate section to understand the system,,its there ,if not ,let me know,i'll post it for you

Edited by govtech4
56napco Enthusiast

56napco

Posted
  • Author
Posted

Ok, so the manuals say exactly what is already posted. I understand what a predetermined value is... what no one can seem to tell me is what that acutal value is. Is it 1/4 tank, 1/2 tank, empty?

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted (edited)

the answer is no one knows ,!!!

 

from the service manual ....

 

 

 

Secondary Fuel Pump (Dual Tank Applications Only)

 

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.

 

good luck on your search for the answer

Edited by govtech4
txab Senior Enthusiast

txab

Posted
Posted

It's not designed to let the main tank get really low then fill it back up. At the predetermined level the rear tank will begin to fill the main tank, then shut off, until the main tank level drops again. The process begins again. It is designed, as it was explained to me, to keep the main tank at a fairly constant level until the aux tank is empty. Another words you're probably not going to see the gauge drop down and then begin to rise.

 

Why are you needing to know the exact point at which the transfer begins to take place? The systems work great, except in the case of a pump failure

56napco Enthusiast

56napco

Posted
  • Author
Posted

The main reason I wanted to know is so I know my fuel system is working correctly and what to expect. I'm not fully convinced it's working the way it should based on the gauge readings and number of gallons it will take to fill.

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

im real sure there are tests the system does and when it fails ,it puts on the SES light ,,

 

others can chime in to verify that ,i remember up north a 2 tank system had problems ,cant remember what model

  • 2 weeks later...
testdrive Enthusiast

testdrive

Posted
Posted

I had a dash mounted led light wired so it would turn on when the transfer pump would run. It would first come on about 2/3 tank and run for 5 minutes and then go off. Its time on cycles were between 2/3 and down to 1/2 tank. You never saw the gauge do anything except continue to drop in the normal 8.1L manner. :tear: My rear tank is 11 gallons, front is 26, total of 37. This method is used on all of the two tank Suburbans, Yukon, and medium duty 3500-5500 series trucks.

I studied this in preparation for my transition from the 8.1L to a LBZ Duramax in my 2003 2500 Suburban.

And the system will set a code if the sending units don't report readings properly.

  • 1 year later...
  • 1 year later...
72chevy72 New Member

72chevy72

Posted
Posted

I had a dash mounted led light wired so it would turn on when the transfer pump would run. It would first come on about 2/3 tank and run for 5 minutes and then go off. Its time on cycles were between 2/3 and down to 1/2 tank. You never saw the gauge do anything except continue to drop in the normal 8.1L manner. :tear: My rear tank is 11 gallons, front is 26, total of 37. This method is used on all of the two tank Suburbans, Yukon, and medium duty 3500-5500 series trucks.

I studied this in preparation for my transition from the 8.1L to a LBZ Duramax in my 2003 2500 Suburban.

And the system will set a code if the sending units don't report readings properly.

Old post, but I could use some info on this -

 

I have a similar swap - 2002 Yukon Xl - dual tank - with the LBZ - I have most everything sorted out, but the secondary fuel tank does not transfer to the primary.

 

Quick Question - do you have a wiring diagram for the secondary pump, or do you remember the wire colors for +/- to energize the pump - I will be installing a manual transfer switch.

 

Thanks!

  • Like 1
  • 3 years later...
superdeeduper New Member

superdeeduper

Posted
Posted

so the last post in this thread on 11/19/2014.  did you ever get it figured out? (reviving an old post but this is the problem i'm having.)  i've got an 08 suburban w/LMM.  i'm guessing my secondary tank is not working because my last 2 fill-ups have only taken 24-ish gallons (roughly the size of the primary tank only) AND gas won't run into the filler hole at anything but a painfully slow rate when i'm re-fueling so i'm guessing the secondary tank pump is not activating and the tank is staying full and also preventing normal filling.

  • Like 1
  • 5 weeks later...
swathdiver Senior Enthusiast

swathdiver

Posted
Posted
On 8/17/2018 at 6:43 PM, superdeeduper said:

so the last post in this thread on 11/19/2014.  did you ever get it figured out? (reviving an old post but this is the problem i'm having.)  i've got an 08 suburban w/LMM.  i'm guessing my secondary tank is not working because my last 2 fill-ups have only taken 24-ish gallons (roughly the size of the primary tank only) AND gas won't run into the filler hole at anything but a painfully slow rate when i'm re-fueling so i'm guessing the secondary tank pump is not activating and the tank is staying full and also preventing normal filling.

Is your Suburban on a 1500 or 2500 chassis?  

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.

  • Forum Statistics

    250.5k
    Total Topics
    2.7m
    Total Posts

  • Member Statistics

    342,914
    Total Members
    8,960
    Most Online
    AidenVorpagel
    Newest Member
    AidenVorpagel
    Joined

  • Who's Online   1 Member, 0 Anonymous, 545 Guests (See full list)

  • Latest Articles

  • Posts

    • Grumpy Bear
      Sugar Bears 2015 GMC Terrain SLE-2 2.4 AWD

      By Grumpy Bear · Posted

      286,740 Mile Services   8/6/2026   New AC Compressor. Refrigerant oil and dye, evacuate and charge system.  New exhaust system from cat back.  New Iridium plugs plus replace #3 coil Repair/rewire headlamp wiring (passenger side) and replace all forward bulbs. Polish lenses of both assemblies.  Pull rear rotors, clean and adjust parking assembly. Inspect, clean and grease front calipers. Check pads and shoes.  4 wheel power bleed of brake system. Dot 4 Reset idle speed 50 rpm higher New Serpentine belt.    Will need new pads in the rear in about 5K more miles.    Tax Title and License out the door just short of a grand.    AC clutch had bitten the dust. 1 year warranty on the pick and save replacement. Thing will make a Polar Bear cry Uncle.  He spent quite some time on the wiring. It was in the harness and he does nothing half. I got off cheap. I have considerable more light down the road. Sylvania Silver Star replacements.  Gas seal between the porcelain and shell of plug #3 was blown, cooked the coil. That was the cold miss.  Love the new exhaust. I can sneak into the neighborhood again.  Nice to have a working parking brake again. Belle Tire never got it done. That was disappointing.    This was one of her bigger bills and still way cheaper than a payment even given the oil consumption. This thing cost me under a hundred a month in repairs and normal routine costs. What is my incentive to replace it? 🤔           
    • AidenVorpagel
      cam upgrade in CA

      By AidenVorpagel · Posted

      hello I recently bought a 2012 gmc 1500 with a 5.3 and have a AFM disabler on it I'm interested in doing a cam but I'm worried if I remove the AFM system I will fail smog does anyone have info if they are able to detect that or a work around to it (not talking about hot smogging) please let me know thank you  
    • B14Sierra
      Noise after AFM delete

      By B14Sierra · Posted

      Did you figure it out?
    • B14Sierra
      Possible lifter tick after DOD delete

      By B14Sierra · Posted

      Update. I started chasing down my symptoms. Started first with pulling valve covers and looked at everything. Everything looked good and couldn't hear or feel anything different. Then a compression test. 240 psi or really close on each cylinder. I was worried I was a tooth off of timing. Not bad for an engine with 173,000. Granted I did put new heads on. I sprayed water around the injector area to see if I could hear a change. Nothing. I hooked up my new hp tuner which I should have done in the first place but I don't really know what I'm looking at just yet but am learning. I noticed the fuel trims were way off so that told me I have to have either a bad injector or exhaust leak. New injectors, so I did the shop vac on blower and in the tail pipe. Sprayed soapy water and found the exhaust flange on the drivers side was leaking. I didn't think it would be that considereding I pulled the heads and left the manifolds attached. I did have the transmission replaced not long ago. They must have not seated them properly but I guess I didn't notice. I put in new gaskets on both sides. Which by the way isn't a bad job but I had a hard time getting them to seal right. Took two attempts. Reset the fuel trims and the ticking is gone, engine runs smooth and acceleration has improved. Got to feel the real difference with that stage 1 cam. It's not that big of a difference but it does add a little more. It feels like how the truck should have been from the factory.
    • Grumpy Bear
      Some Assembly is Required

      By Grumpy Bear · Posted

      Can it still be Assembled I?    Stribeck says that we need a certain amount of viscosity under conditions of load and velocity to prevent two surfaces of a know roughness from tearing each other asunder. And we have marketing trying to tell the masses that those two surfaced require less of that commodity due to more exact limits being placed on the same old clearances. We also know that there are limits to how hard something can before it becomes to brittle to be viable and to smooth to 'wet' the surface and that both of those conditions have been known and met since about the Second World War.    That viscosity value shook out at 10 centistokes at 212 F just under a hundred years ago.  Give this a look: [Anton Parr]     What is advertised is the Kinematic viscosity (mm2/s) or that which has been density adjusted but the value we are after is the dynamic viscosity (mPa.s) or true viscosity. You can see that this number is dependent on density thus base stock and temperature. You can also see that an SAE 30 doesn't reach that value in this example. However an SAE 30 that is at the upper end of the SAE 30 range; 12.5 cSt (mm2/s), might. 12.5 * .83 = 10.375 (mm2/s). If you could find an SAE 30 at the upper end these days.   Then there is the complication of viscosity modifiers or VII or VM, whatever you wish to call them. Polymers added to very thin base oils, perhaps 3 to 6 cP oils, that will meet the SAE *W30 spec at 'tested' shear rates and 100 C/212F  target temperature. So a polymer fortified base that is a fraction of the 10 cP requirement Stribeck insist upon.   This could be all well and good if those polymers didn't have two very problematic 'features'. They shear or loose viscosity both 1.) permanently and 2.) temporality. And they do both omitted in the advertised data with the distinct  purpose of deceiving the consumer of the actual operating state of the fluid. I've shown the example of Warren Oils COSTCO 10.91 cSt 5W30 formuation several times where the 100 C HTHS value is 6.9 cP!! That's the temporary shear down and with and SSI or shear stability index of 9.4 cSt. Note the intentional deception in using mixed units?    After a short while that 9.4 cSt oil has a viscosity corrected dynamic value of 7.8 cP. But as the SSI is still within the range of an SAE *W30 whose lower value is 9.3 cSt.    This allows them to continue to call this SAE 16 weight oil a 30 weight, the cake, and still meet the API requirements for fuel efficiency IMPROVEMENT mandated by the EPA. The eating of the cake. By the time you've worn out your motor doing the responsible thing by adhering to the warranty requirements, (the stick), you get deprived of the carrot, wear control. So sad, to bad.   So what can be done? Do I need actually say? [Anton Parr]       Even this must be monitored if the oil is on the low side and the VII an organic or you opt for a 0W40 with an even lighter base oil and more / higher MW VII. (Note the lower density of the 40 weight versus the SAE 30 mono-weight?)    There is another workaround. Temperature. An SAE *W30 run at a bulk temperature of between 180 and 195 F.    Being the belt and suspenders sort I am I do both. Run it cook and run it heavy.    In Part II I'll work the AW package. 

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...