Hi guys. I'm new here and just bought a 12 gmc 3500hd cab and chassis. one ton dump, Duramax, I immediately started having issues with the dual tank system. My problem is the rear tank is overflowing the front tank. the fuel gauge only reads from about 1/4 down. Would a bad fuel level sensor in the front tank cause the ecm to overfill the front tank? Also I'm having a hard time finding the correct part number for the front tank's pump, it's the 22/23-gal tank in front, 40 in the rear, anybody know the front pump part #, This morning was really cold, the truck started but would not go to high idle, then started dieseling and stalled and would not restart, A little later I primed the pump and it started, It went to high idle this time but stalled out shortly after, I don't hear the pump running. Any suggestions would be appreciated. Thanks
dual tank woes
- Thread starter steve12gmc
- Start date
Welcome.
Yes, a bad level sensor in the front tank can cause over filling. The rear doesn't know when the front is full so it keeps pumping
The LML doesn't have any lift pump in stop form so if your supply line has a leak, either at the hose, filter or fittings it can start sucking air and cause it to stall like you witnessed. I'd make sure to get that fixed as those CP4 pumps don't like to be starved of fuel or run dry
Also moved thread to fuel and exhaust
Yes, a bad level sensor in the front tank can cause over filling. The rear doesn't know when the front is full so it keeps pumping
The LML doesn't have any lift pump in stop form so if your supply line has a leak, either at the hose, filter or fittings it can start sucking air and cause it to stall like you witnessed. I'd make sure to get that fixed as those CP4 pumps don't like to be starved of fuel or run dry
Also moved thread to fuel and exhaust
Thanks, It looks like I have other problems now, It won't start at all, even after priming, it just cranks, and with the key in run, I have no power going to the pumps. The 2 fuses in the box under the hood are ok. I have 2 in tank pumps, (front & rear) and one inline pump, none have power. Any suggestions would be greatly appreciated. thanks
I could be wrong, but I'm pretty sure you only have a transfer pump to move the fuel from the back to the front tank. A transfer pump module and two senders.
The CP4 up at the engine sucks the fuel from the front tank. Under normal conditions you won't hear any pump running. I forgot the numbers, but I think it's something like, when the front gets down to 1/4 the transfer pump moves fuel from the rear to the front. I don't remember what level it stops at. Maybe 3/4. It will do this until the rear is empty
If there is any air leaks in the line running from the front tank to the CP4, it will make starting hard or not start at all. You can replace the fuel line after the filter housing with a clear line to see if it's sucking air or not. Some have been successful with pressuring the tank with a few PSI of air to force fuel up the line and push air out.
Do you have any scanner that can monitor fuel pressure? Without one we are all just guessing
Edit, this thread has some good information on the dual tanks:
www.duramaxdiesels.com
The CP4 up at the engine sucks the fuel from the front tank. Under normal conditions you won't hear any pump running. I forgot the numbers, but I think it's something like, when the front gets down to 1/4 the transfer pump moves fuel from the rear to the front. I don't remember what level it stops at. Maybe 3/4. It will do this until the rear is empty
If there is any air leaks in the line running from the front tank to the CP4, it will make starting hard or not start at all. You can replace the fuel line after the filter housing with a clear line to see if it's sucking air or not. Some have been successful with pressuring the tank with a few PSI of air to force fuel up the line and push air out.
Do you have any scanner that can monitor fuel pressure? Without one we are all just guessing
Edit, this thread has some good information on the dual tanks:
2016 C@C dual tank system help
Hello, I couldn't get my old login so I made a new one I'm formerly Catman3126 Okay I have 2016 C@C duramax that has the dual tank setup and he is having issue with it running out of fuel and the gauge dropping to zero randomly, does anyone have the GM Systems operation of how this system...
www.duramaxdiesels.com
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thanks, I read there are no in tank pumps in the dual tanks lml trucks, that would explain why each sender only has 2 wires at each plug. so the only pump is the inline pump in the rear left frame rail? I have no power at the inline pump or senders. can you run a jumper to the inline pump and crank to test?
There is only a transfer pump. If you jump out the relay it won't do anything to help get it started unless your front tank is empty.
If you want a lift pump you're going to have to install one. @Bdsankey is a vendor here and can help you select one if you desire
When you pump the primer, does it get hard before cranking?
If you want a lift pump you're going to have to install one. @Bdsankey is a vendor here and can help you select one if you desire
When you pump the primer, does it get hard before cranking?