LLY: LLY Cab+Chassis fuel tank issues

[dirtymax36]

Currently dealing with not having a fuel guage. Truck came in with the rear fuel tank and transfer pump locked up with 3 year old diesel in it. I did away with the secondary tank and such and just ran one tank. The ecm is now tuned accordingly like any ol 3500 single tank truck.

Theres currently 2 wires (purple+black) on the first larger tank sending unit and then 2 wires (blue+black) that go to the secondary sending unit tank. Do i need to wire any of these wires together on the rear tank or put a resistor in it ? Im getting 0% fuel level according to my V2. No codes either, I also have 5 volts constant to both tank sending unit power wires. If i tie both of them together my V2 says its 100% full with 68 gallon remaining. Any ideas? Trying to avoid putting a new second tank back in it since it was pointless..

 

[clrussell]

Does the truck have a non cab and chassis tune in it? Code in the ecm for fuel transfer pump?

 

[dirtymax36]

The truck has just a modified dsp5 version of the stock file. Secondary tank voltages are all set to 0 now and secondary fuel tank capacity is set to 0 as well now.

Can I switch a stock tune but different OS on this and not have any issues ?

 

[dirtymax36]

My current OS is 0516005. Can't seem to find anything else with that OS

 

[clrussell]

If your using a modded stock file for that truck that's your issue I bet.. if it's not seeing transfer pump it'll throw a code and default to empty on the gauge

 

[loganater]

if it were me i would zero out F0102 in efi live and leave the blue+black wires open. ecm is not going to look for a value above 0 on the second tank. then go to f0301 and put in the main tank gallon size. if you have a 5 volt refrence on one side of the level guage then you should at least have some kind of return voltage that the v2 should see on the main tank

 

[clrussell]

Flash a 3/4 ton os in it and see what your gauge does

 

[loganater]

*level sender not guage

 

[THEFERMANATOR]

Your cab and chassis stock file will never work correctly with just 1 tank. The correct fix is to take your stock file and do a segment swap with an OS from a truck with a single tank, then go in and input the correct single tank size and voltages for each voltage step in the level chart for the primary tank(leave the secondary zero'd out), disconnect the rear tank sender wires, then you will have your gauge back. Even if you zero out the rear tank size, the ecm will still look for voltage movement on the rear sender. If it doesn't see it, it will revert the gauge to empty. And your os number has nothing to do with this, it's the fuel system segment that deals with the fuel gauge and tank arrangement.

 

[clrussell]

Your cab and chassis stock file will never work correctly with just 1 tank. The correct fix is to take your stock file and do a segment swap with an OS from a truck with a single tank, then go in and input the correct single tank size and voltages for each voltage step in the level chart for the primary tank(leave the secondary zero'd out), disconnect the rear tank sender wires, then you will have your gauge back. Even if you zero out the rear tank size, the ecm will still look for voltage movement on the rear sender. If it doesn't see it, it will revert the gauge to empty. And your os number has nothing to do with this, it's the fuel system segment that deals with the fuel gauge and tank arrangement.

Thanks ferm.. that's whst I was trying to say butbwithout the exact reason lol.. because I didn't know why

 

[mamumtsllc]

I did the same thing with my dad's 02. Pulled the back tank. Went in and changed the fuel capacity to just the front tank and killed the codes for the 2nd sender. His gauge works fine. You may have a sender problem. I've replaced a bunch of them acting like yours. Hopefully not tho.

Sent from my SAMSUNG-SM-G891A using Tapatalk

 

[dirtymax36]

Correct. Forgot to post my results but other than in EFI changing it to the capacity of one tank and shutting off the codes to the second tank and then wiring the female truck side plug on the tank sending unit to match. Been working with no issues since August, thanks guys!