I don’t know what your fuel capacity is but I do know every diesel I ever drove pulled fuel from both tank’s I have never seen one with a tank selecter switch as far as the foaming and cutting off do not stick the nossel in all the way to give room for
the air to escape.
I can hold the nozzle outside the truck and it foams up fast no matter how slow I pump. I’m this truck from what I understand. When the front tank is 2 gallons lower than the rear it pumps from the back to the front. The front is the only one that supplies the engine.
You may have a bad vent in the tank not letting the air out as far as the front tank supplying the engine you are right a fuel line between the tank’s so it can pull fuel from both you can check this if the fuel guage works when you get low on fuel just fill the back tank the guage will stay the same as when stopped but it will get higher as you drive till the tank’s level 0ff.
I hate to admit what it was but Chevrolet got me thinking. Both incidents happened at about the same mileage. So I discovered the fill tube for the front tank went up then down and up and down again.
I was never getting the front tank all the way full. The back tank was pumping to the front but because the gauge flops around it wasn’t doing it as it should.
While I did fix some things I had codes for essentially I ran the front tank out of fuel twice.
So next step is to fix the fuel balance / gauge issue.
I had filled up with diesel sitting at the top right under the caps. Waited a long while and it didnt go down. Drove 45 miles and since fixing the filler tube I just squeezed 18 more gallons in the front tank. Yippie
Let me know if you need to know the resistance values for the front and rear fuel sending units. If so, I’ll try to dig them up for you.
Thanks! I appreciate that. This is a link to a how to on it that I found. Couple posts in it gets pretty detailed. Hopefully this is correct.
Every time they called and said it was ready and I had them check more stuff and got to the next point.
I kept asking one question to the dealer. How does a truck that appears to be filled to the top with diesel run out in 200 miles. They couldn’t answer. Something so simple to cause such a headache. Good thing I like a good mystery
Had the technician taken the truck to a fuel station and tried to add 40 gallons of diesel fuel to the tanks he may have discovered problems, however they normally rely on input from the driver of the vehicle for what problems need to be addressed.
As far as the amount of fuel to travel 200 miles, expect 10 to 15 miles per gallon, depending on type of use, don’t expect the 20 MPG that some people boast about.
Isn’t it great though to have the problem figured out?
Heck ya it’s great! I’m not hating on the dealer. Their inability to answer the question put me on the right path. I haven’t used a repair shop in over 15 years. I fix things myself. I didn’t get it first go round
Glad you are back on the road with a reliable vehicle OP. My truck has two gas tanks. I have to move a lever to switch from one to the other. If the tank I have selected runs out of gas the engine will stall, even if the other tank is full. When the engine is running fuel is being pumped out of the selected tank by the fuel pump and whatever fuel isn’t needed at the carb flows back to the same tank in the return hose. I think that’s part of the reason why the tanks have to be manually switched rather than just drawing from both tanks. In my truck’s case the tanks are not at the same level. It seems like if two tanks are at the same level (height) and connected together at the bottom though they could be treated as a single tank.
OP’s truck doesn’t use a tank selector switch
Only the front tank feeds the engine
There is a rail-mounted transfer pump which moves fuel from the rear tank to the front tank
So I went over the diagnostic procedure. My truck is already on its 2nd balance module from the previous owner. I read how many people even after going to the dealer never got the system back to 100% perfect or if they did some darn part would go bad again after a couple years.
So I went a different route. A more manual setup.
I unplugged the balance module. Cut 2 wires from the harness and tied them together. Now the fuel gauge doesn’t flutter and reads right. It is only reading the front tank. Since that one feeds the engine that’s the one I care about.
I cut 2 wires from the fuel pump relay next to it and ran a wire up to a spare toggle switch on the dash. I can now manually operate the transfer pump. It’s no longer powered any other way.
So when the gauge reads half I will flip the switch and fill it up pumping diesel from the rear to the front. When it reads half again do the same. When it gets low this should be fill up time as the tanks are only a few (I think 4) gallons different in capacity.
This also makes any future problem in the system much easier and faster to diagnose.
You could use another toggle switch 3 way and flip the gauge to read the front or the rear tank in this setup… I wasn’t that bored today and didn’t see any point with the extra work.
I think somebody replaced the balance module, because their diagnostic skills were woefully inadequate
It’s almost always a defective sending unit, not the balance module
The rear sending unit was my conclusion. 30 minutes to simplify the system and spend no money won out. I already had a bit of unnecessary money in this project not to mention while this was going on I noticed the pulley on the vacuum pump intermittently not spinning. That was a few more bucks and 6 tires are going on this week, along with new oil cooler lines. All good I have a extra pmd and I feel good with knowing the lift pump is new.