dual fuel tanks

[Cwalt50]

Hi I got a 05 c&c 3500 dmax and I already replaced the rear tank sending unit and the the transfer pump because the gauge didn't work and they was bad. I cleared the codes and it read correct for a day or two and read empty again. Went to fill the tanks and the front tank was full and the back was about half and it keeps reading empty. Everytime I clear the codes it works for a little then stops again. I was looking and found that theres a tsb out for that problem and one of the things is it needs to be reproggrammed. My question is can I do the reprogramming needed with efi live? I have a v2.

Thanks,
Cliff

[Chavez91]

Go to GM TIS2Web and look up the vin for that truck. It will give you the proper updated OS # and segment #s. Find a stock file that has those and flash them in and you should be good to go.

[Cwalt50]

Thanks I just checked into it and I have all the most up to date os# and segments#s already

[THEFERMANATOR]

Sounds to me like your transfer pump is sticking on. Anytime the ECM sees fuel move when it thinks it shouldn't, or a change in the senders value that doesn't correspond with what it thinks should happen, it makes the gauge read empty, and disables the transfer pump. The ECM will take the value from both senders, and give 1 value to display on the gauge. Once the front tank gets to around 75% I believe is what testing from somebody else came up with, the ECM turns on the transfer pump to move fuel forward, and will stop the pump around 80% on the front tank. If the front level continues to rapidly drop, go up to quickly, or continue to rise after the pump is commanded off, it disables the pump and goes to E on the gauge. Also if it does not see the rear level drop accordingly to how much it expects it to after running the pump, or for it to continue to drop after the pump is commanded off, it will disable the system and send the gauge to E as well. It's a basic system, but has ALOT of safeties built into it.

[Cwalt50]

I put a new rear sending unit on and also a new transfer pump and fuel lines on too. The only thing that's still original on it is the front sending unit