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Discussion Starter #1
I have an aux tank that is wired into the fuel gaging system. The fuel low light has worked fine on both tanks until recently. I could let the light come on and then switch tanks and never miss a beat. When on the aux tank the tank ran dry with no low level indicator on two occassions. The gage was indicating low but not totally empty. The engine began to shutdown and that ain't good. I have not tried to check it on the OEM tank but since it worked OK before I assume the gaging system is OK.


Does the low light get all of its input from the gage wiring and if so how can it not work and the gage work OK? What do I check to isolate this problem? I feel like that the problem is in the light activation circuit.


Tom
 

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What are you using for a sending unit in the aux tank? I believe the low light comes on after seeing a signal from the pcm when it see's below a certain percentage of fuel level.


I have to be honest with you all, I have never messed with adding tanks/valves so I really only have suggestions. I appreciate other people helping me out with these.. Thanks


Eric
 

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I have an aux tank plumbed with a fuel switch that selects which tank as well as switch the sending unit the OEM gauge is reading from. As far as I know, the voltage sent to the gauge from the tank's sending unit is what signals the Low Fuel light to come on.


I have had to adjust my sending unit's float arm in order to get it to read more accurately. If your light came on at one time and now does not, it is my opinion your sending unit float arm needs to have a minor adjustment.
 

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Discussion Starter #4
dmaxalliTech


I have the float unit. Since it is wired into the truck system (spliced in) I would think it should work just like the OEM since the OEM is also a float sending unit. I think you are saying it goes into the computer to turn on the low level light.


I am going to tinker with the aux tank float adjustment like RV Guy suggested. My son has a new Blazer that was getting a low fuel light prematurely and he took it for service and they had to reprogram the computer. They indicated that it was known problem. His is an 03 and mine is 01 so I suspect the two are not related but thought it might be possible.


I may have to put fuel in the aux and run the OEM tank down until it comes on but down don't want to chance running the engine out of fuel.


Tom
 

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Tom,


I believe you are correct in that the voltage from the sending unit is being read and light turned on at a specific voltage. Problem is they are obviously different sending units and need to be aligned voltage wise for the light to turn on at the appropriate time.


I think I finally have mine adjusted where I want it. Took several adjustments over a long period of time. Finally, this weekend, on a long trip I intentionally ran the aux tank down toward the "E" gritting my teeth hoping the light would come on before it ran out of fuel.


With the needle reading one mark above Empty, the light came on. Now I want to refill and determine exactly how much fuel was left in the tank. I tow our RV trailer allot and get about 10 mpg towing. So I want to have about 7 - 8 gallons left in it when the light comes on.
 

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Discussion Starter #6
RV Guy


Mine used to come on at the same point yours does. I add some fuel to the aux tank tonight and am going to let the OEM tank get down low where it is suppose to come on. If it does not then I know it is the truck system and not the gage system in the aux tank.


I always switched my tanks when the light came on and every time I refueled it had about 3-4 gal left in the tank. That is pretty thin on the bottom considering the surface area of the tank. I was in the mountains with my TT one time and it ran out before the light came on but I know it was because of going up and down hill. The engine sensed a massive fuel leak and went into limp mode. I limped up a two mile long 5-6% grade in first gear. It finally got rid of the air and ran OK but the SES light stayed on until it was cycled 5-6 times and turned the light off. The code stayed. That's how I knew what it set.


That senario didn't happen the last two times this occured with the light not coming on. I guess I need to readjust the float but don't want to fool with it until I get an answer on the light even working or not.


I also get an average towing of 10.5 MPG over a trip and not just one tank full.


Thanks for your reply.


Tom
 
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