Replace 31 gallon tank with 39 gallon tank from 2500 series Suburban?

[strutaeng]

what is Tech-2?

Is like the factory/dealership scanner/diagnostics tool.

 

[gooffeyguy]

My low fuel warning light will usually come on when the gauge is almost on the last mark. When I fill up it will take 25-26 gallons, so I know I have about 5 gallons left. The "Fuel Used" info on the DIC is pretty accurate with this on my vehicle, usually only a tenth or two off. For example, it'll say 26.3 gallons used and a fill will take 26.1 gallons. Only time it's been like a gallon or two off is that first tank if I switch from filling up with E85 or 93 or back

 

[petethepug]

That’s how mine was when purchased in 2020. Accurate enough to get me through AZ desert with needing a 30 gal fill up at an oasis gas station. Then it slowly got worse as carbon pellets invaded the tank.

With the pellets run out like a bad mouse infestation, I can cram almost 32 gal in the tank (not recommended) because the low fuel warning properly alerts at about <2 gal left and stalls truck if parked on steep downhill.

GM OEM stuff is pretty impressive. My daughter’s 01 s10 with 36k orig miles finally has the fuel sender off by a 1/4 tank. The pump is still ok.

 

[swathdiver]

what is Tech-2?

It's the dealer level scan tool that these trucks were designed to be worked on with. It was replaced in 2014 with the MDI and later the MDI2 but still works on our cars, not the new ones.

 

[swathdiver]

From the shop manual for the long body 1500 GMT900s:

 

[petethepug]

Low fuel on (<3.8gal) goes really fast when using e85. Only ran out once. It was corn gas and I had hoped to avoid replacing the f/p after the carbon pellet contamination.

Waiting 90 min for AAA to bring fuel sucks. That was the deciding factor to get a new f/p and pull the tank. Can not have the wifey & kids getting stuck like I was because of an inaccurate sender.

BTW I also called OnStar for fuel to see if their road service would get it faster than AAA. Nope. 3 hour wait with o/s. Apparently when you call o/s for fuel they send out a call to all participating service contractors. The only one that answered the call was 30 miles away through rush hour traffic. Just say’n, you get what you pay for because I was on a free trial with o/s at the time

 

[strutaeng]

The 2500 Suburbans have a dual tank setup (with a fuel pump/sender in each tank). The auxiliary tank is like 7 gallons, and main tank is 30 gallons(?)

The system is kinda more complicated because you have an extra relay for the auxiliary tank, there's extra wiring and it's tied into the cluster for the fuel level (via the Class 2 data bus system or whatever that thing is called?)

If you study the wiring diagrams, I'm sure it's possible to swap the dual tank setup. I can't remember if HP Tuners has any sort of settings to enable dual tanks on the ECU side of things...I can check.

I'm looking to see if an 8.1/Allison 5 speed can be swapped into my 04 project Suburban 2500...

I was looking at my Suburban's HP Tuners tune and it looks like this for the dual tank setup. I'm not sure what all these numbers are TBH.

I'm gonna power up the 04 8.1 engine's ECU and see if I can replicate this information on that tune. It'll have to look at the wiring diagrams again, but I seem to recall the secondary tank fuel pump has it's own relay and it's all tied to the serial data somehow. But there IS an additional connector on the ECU.

 

[t_bergman]

The one other item to consider is the fill time for the two tanks; when the pump clicks off and I give it another one minute to rest I can get another 3-4 gallons in the tanks which means that there's some sort of air release process which needs to occur. Happened in my 09 and also in my 2013. I'm assuming this process needs to be engineered right and would be hesitant in a non OEM solution.

The 39 gallons is handy though; back when I was in college and could withstand the longer drive without stopping I had a 700 miles drive between my apartment and home, setting the cruise to 65 mph got me 19mpg and could do the whole drive in 11 hours without stopping.

 

[Geotrash]

The one other item to consider is the fill time for the two tanks; when the pump clicks off and I give it another one minute to rest I can get another 3-4 gallons in the tanks which means that there's some sort of air release process which needs to occur. Happened in my 09 and also in my 2013. I'm assuming this process needs to be engineered right and would be hesitant in a non OEM solution.

The 39 gallons is handy though; back when I was in college and could withstand the longer drive without stopping I had a 700 miles drive between my apartment and home, setting the cruise to 65 mph got me 19mpg and could do the whole drive in 11 hours without stopping.

I used to have a BMW diesel that would go 650 on a tank. Never made it that far because it exceeded my bladder range. But I used to drive Boston to Denver and back fairly often, and it was 3 fuel stops and less than $200 in diesel, and I’d arrive home in Denver with almost a full tank.

 

[KidWgn]

I used to have a BMW diesel that would go 650 on a tank. Never made it that far because it exceeded my bladder range. But I used to drive Boston to Denver and back fairly often, and it was 3 fuel stops and less than $200 in diesel, and I’d arrive home in Denver with almost a full tank.

Hold on..................does your sig say THIRTY FIVE HUNDRED!? Where the hell did you find one!? Is it an armored variant?!