fuel gauge to empty 2020 Silverado Duramax Allison Crew Cab SB

[Coop]

I installed a transfer tank in my truck for extended range. I can transfer fuel into the factory tank without an issue but at some point after the transfer, I'm talking hundreds of miles, the truck goes to "empty" on the fuel gauge. Service writers at two different dealerships are telling me that the program in my truck is the same as a dual tank cab/chassis. My computer is seeing the factory tank filling when is should be using fuel so it "shuts of the nonexistent transfer pump and has the gauge go to empty." They say there is not a fix for this. Pretty much defeated the transfer tank install.

Is there a fix?? Ideas??

Thanks,
Mike

 

[Chevy1925]

Lol they are kinda right. It’s not a dual tank issue, gm doesn’t flash calibrations in trucks like that. It either gets the segments for dual tanks in the operating system or it doesn’t. EPA wouldn’t approve of it.

That said, it’s going to go to empty if you are filling while moving and not letting fuel drain down in the main tank. The computer and self checks see a climbing fuel gauge as the vehicle is consuming fuel as an issue and can throw codes/kill the gauge from it. It may work if you allow a bigger swing of full to empty to full again to happen.

Are you only letting it go to like, 3/4 full then filling it? Try going to 1/4 tank and then filling.

 

[2004LB7]

As James said. If the ECM doesn't see the fuel level sensor move for x number of miles then it assumes its bad and puts it on empty. But once it sees movement then it will put it back to the correct position. Some have had luck with efi live or HP tuners and adjusting the tank size

 

[Trimox]

Put an electric valve on your transfer tank, don't just let it stay full till transfer it empty. Let the fuel gauge move some. I never shut my truck off when I stop for fuel and it never goes to empty.

About to do something similar. Just a thought.

 

[Coop]

My tank is a Titan Trekker 50 gallon, it transfers 5 gallons at a time, nothing happens automatically.

Is it possible to change things over so that the transfer tank is wired and plumbed in like the second tank on the cab/chassis trucks?

 

[2004LB7]

My tank is a Titan Trekker 50 gallon, it transfers 5 gallons at a time, nothing happens automatically.

Is it possible to change things over so that the transfer tank is wired and plumbed in like the second tank on the cab/chassis trucks?

Yes. You'd need to hook up to the pins on the ECM to power the transfer pump relay along with the, i believe, second fuel level sender. Then get the dual tank calibration loaded up

 

[Chevy1925]

Dealer will not load the dual tank calibration. You will have to have that done via HP tuners or another source. Then if you want warranty work done, they will not touch anything as the calibration flashed in will not match the gm one.

So, pick your battles. If you still have a warranty and like having it, don’t flash the computer

Also, I’d bet the dual tank is not a transfer style. Instead both tanks will drop level equally. This way the fuel needle moves accurately to the amount of fuel left. Otherwise you have no way to monitor how much fuel is in the rear tank. Engineers don’t like seeing the fuel gauge stay pegged full for 500 miles before it will finally start to move cause the rear tank is finally empty

 

[Coop]

Dealer will not load the dual tank calibration. You will have to have that done via HP tuners or another source. Then if you want warranty work done, they will not touch anything as the calibration flashed in will not match the gm one.

So, pick your battles. If you still have a warranty and like having it, don’t flash the computer

Also, I’d bet the dual tank is not a transfer style. Instead both tanks will drop level equally. This way the fuel needle moves accurately to the amount of fuel left. Otherwise you have no way to monitor how much fuel is in the rear tank. Engineers don’t like seeing the fuel gauge stay pegged full for 500 miles before it will finally start to move cause the rear tank is finally empty

Which tank is not a transfer style?? Mine or the factory GM tank?

 

[Chevy1925]

Which tank is not a transfer style?? Mine or the factory GM tank?

the factory dual tank does not transfer fuel like your current one does

 

[2004LB7]

the factory dual tank does not transfer fuel like your current one does

I thought the dual tank (cab and chassis) trucks had a transfer pump to move fuel from the rear tank to the front. All controlled by the ECM. Am I mistaken?

 

[JoshH]

I thought the dual tank (cab and chassis) trucks had a transfer pump to move fuel from the rear tank to the front. All controlled by the ECM. Am I mistaken?

The factory dual tank setup does operate like that. The thing is both tanks have a sending unit. The ECM looks at the fuel level in both tanks and makes the gauge read accordingly. What I'm not sure about is how it transfers fuel. I assume it tries to keep the tanks close to the same level, but I don't know if it does it in large increments or small. It could very well keep the front tank full and keep pumping out of the rear tank when the front drops to a certain level. I've worked on several, but I've never driven one enough to know if one tank runs out before the other or if they stay pretty even.

 

[2004LB7]

The factory dual tank setup does operate like that. The thing is both tanks have a sending unit. The ECM looks at the fuel level in both tanks and makes the gauge read accordingly. What I'm not sure about is how it transfers fuel. I assume it tries to keep the tanks close to the same level, but I don't know if it does it in large increments or small. It could very well keep the front tank full and keep pumping out of the rear tank when the front drops to a certain level. I've worked on several, but I've never driven one enough to know if one tank runs out before the other or if they stay pretty even.

I think it's something like when the first tank drops to 75% it turns on the transfer pump and then turns it off at 80%. If it sees the level rise above 80% while driving then it disables the transfer pump. I think it averages the gauge from both tanks

And since the ECM is just cycling a relay, one could hook any pump up to that to transfer fuel from an in bed tank. Just need to wire in the relay and sender to the ECM and program it with the dual tank tune

From what I've noticed, when using the bidirectional tools on EFI live, if you turn on the transfer pump relay on a non dual tank tune, the engine stalls. Weird

 

[Chevy1925]

the factory dual tank does not transfer fuel like your current one does

I’ll have to eat my words, after some research, it does work like this.

On the CC trucks, the rear tank is used first as it continually fills the front tank and the front tank supplies the engine. Front tank is 23 gal, rear is 49 gal. The gauge is setup to read the rear tank for the first 2/3 and the front take for the last 1/3. Obviously with some give or take there and not going into full detail about jt (I’ve not dug much farther). GM also requires you to fill the front tank first, then the rear which would make sense for the way they set it up

Regardless, I don’t even see a CC OS being flashed in fixing the OP’s issue. I see many other people have his same problem…

 

[Coop]

I think it's something like when the first tank drops to 75% it turns on the transfer pump and then turns it off at 80%. If it sees the level rise above 80% while driving then it disables the transfer pump. I think it averages the gauge from both tanks

And since the ECM is just cycling a relay, one could hook any pump up to that to transfer fuel from an in bed tank. Just need to wire in the relay and sender to the ECM and program it with the dual tank tune

From what I've noticed, when using the bidirectional tools on EFI live, if you turn on the transfer pump relay on a non dual tank tune, the engine stalls. Weird

I’m wondering if I could avoid this issue by only transferring fuel when the factory tank is pretty low and never transferring enough in to go to 3/4 or more?

 

[2004LB7]

I’m wondering if I could avoid this issue by only transferring fuel when the factory tank is pretty low and never transferring enough in to go to 3/4 or more?

More than likely

 

[Chevy1925]

I’m wondering if I could avoid this issue by only transferring fuel when the factory tank is pretty low and never transferring enough in to go to 3/4 or more?

Thats what i was explaining earlier. i would say, as long as you are putting in 10 gal at a time or more, you should be fine. there needs to be a decent swing of the needle so the bcm sees it like a fill up. the only other possible issue is if the truck has a problem with the fuel level increasing as the vehicle is moving. chances are low but possible.

 

[Dozerboy]

On my 2006 this problem only happens when the gauge stays at full for like you said 100s of miles. Mine is gravity feed so if I'm unloaded I have to wait until I'm down to 1/4 of a tank to open the valve. If I'm towing heavy I can open it at 3/4s because it fills the tank as fast as I burn it just about.

 

[2004LB7]

Thats what i was explaining earlier. i would say, as long as you are putting in 10 gal at a time or more, you should be fine. there needs to be a decent swing of the needle so the bcm sees it like a fill up. the only other possible issue is if the truck has a problem with the fuel level increasing as the vehicle is moving. chances are low but possible.

With the regulator OS I don't think it cares if the needle goes up while driving. At least it didn't with my LMM. I could go from empty to full by opening up the valve and filling from the in bed tank. But as dozer said it would go back to empty if it stays at full for too long

 

[Chevy1925]

With the regulator OS I don't think it cares if the needle goes up while driving. At least it didn't with my LMM. I could go from empty to full by opening up the valve and filling from the in bed tank. But as dozer said it would go back to empty if it stays at full for too long

2020 infrastructure is far more advance and has far more safetys in it. the fact you cant put a heavier converter in these trucks on a stock tune without setting off injector codes is a testimate to it lol. having engineer friends in the field, ive learned alot about the advancement they put into newer vehicles, its ficken mind boggling what checks and measures are in place.

 

[Coop]

Needed to ask this sooner. If I have the truck scanned I'm presuming there's a code that can be cleared and I can try the above mentioned fuel transfer method to try and avoid the issue in the future.