• If you currently own, previously owned or want to own an Avalanche, we welcome you to become a member today. Membership is FREE, register now!

2500 Fuel System Question

Wingo said:
The rear tank is pretty easy. You'll have to drop the tire, remove the spare tire bracket, then the two tank strap bolts. When disconnecting the fuel filler hoses, I found it easier to remove them from the big tank side, and then just unbolt the fuel filler neck and ground strap from the filler door, it's only three small bolts- easier to get to. Then of course unhook your fuel pump wires and fuel lines when you can lower it enough. Also, while you are at it. I recommend removing the anti siphon flapper valve from the plastic T fitting on top of the little tank, it's the one both filler hoses attach to, you'll see it wobbling in there. It's easy to over tighten those hose clamps and deform it. Do that and filling that thing up will be a nightmare. Ask how I know, had to drop the tank a bit to get that thing out again. I slid the whole flapper assembly out, removed the metal pin and flapper- it's about the size of a quarter, and put the rest back in the T fitting- I felt the T was kinda flimsy without it.

I'm not sure about the gauge reading. There is a float and sender on that pump, I don't know if it is only to shut the pump off when it's empty, or if the truck uses that reading to calculate remaining fuel. I really have no idea.
Click to expand...
I can provide some first hand experience with how the fuel gauge in the dash reads and how large each tank is. I recently bought an 04’ 2500 and the neck of the rear fuel tank was cracked. My first fuel up attempt lead to gasoline just dumping on the ground instead of going into the truck. I ended up cutting the hose leading to that tank and plugging it off so I could at least put gas in the truck. So now I just have the main/front tank operational only.

When I fill the truck up all the way the fuel gauge in the dash only reads 3/4. To verify the main tank was actually filling 100% I fueled up until gas overflowed out of the filler neck. The truck definitely calculates how much fuel is in each tank and then displays a single reading on the dash. Furthermore, I have HPtuners and licensed the truck. The PCM file shows the main tank is 25 gallons and the rear tank is 13 (38 total). Additionally, 25 is 65% of 38 which closely matched my dash read out. Even further I “tuned out”/deleted my rear fuel tank in the PCM file to see if I could get my fuel gauge to read correctly for only using the main tank. I was successful and now when I gas up I have an accurate fuel reading. I usually fill up at a 1/2 tank and I routinely put in 12-13 gallons.

Summary: fuel gauge takes a reading from both tanks and a single reading is calculated by the PCM. The main tank appears to be 25 gallons and rear appears to be 13 gallons.

I will be attempting to replace my fuel lines and the rear tank in the next few days. I’ve found full replacement fuel line kits for 02-03 trucks but not 04 and newer. Does anyone know if the 02-03 kit would work? I reached out to fine lines / sstubes.com and they didn’t think their 02-03 kit would work on an 04 because the evap and emissions systems allegedly were changed in 04. Any insight would be helpful. Thanks
 
Last edited:
8100Avy said:
I can provide some first hand experience with how the fuel gauge in the dash reads and how large each tank is. I recently bought an 04’ 2500 and the neck of the rear fuel tank was cracked. My first fuel up attempt lead to gasoline just dumping on the ground instead of going into the truck. I ended up cutting the hose leading to that tank and plugging it off so I could at least put gas in the truck. So now I just have the main/front tank operational only.

When I fill the truck up all the way the fuel gauge in the dash only reads 3/4. To verify the main tank was actually filling 100% I fueled up until gas overflowed out of the filler neck. The truck definitely calculates how much fuel is in each tank and then displays a single reading on the dash. Furthermore, I have HPtuners and licensed the truck. The PCM file shows the main tank is 25 gallons and the rear tank is 13 (38 total). Additionally, 25 is 65% of 38 which closely matched my dash read out. Even further I “tuned out”/deleted my rear fuel tank in the PCM file to see if I could get my fuel gauge to read correctly for only using the main tank. I was successful and now when I gas up I have an accurate fuel reading. I usually fill up at a 1/2 tank and I routinely put in 12-13 gallons.

Summary: fuel gauge takes a reading from both tanks and a single reading is calculated by the PCM. The main tank appears to be 25 gallons and rear appears to be 13 gallons.

I will be attempting to replace my fuel lines and the rear tank in the next few days. I’ve found full replacement fuel line kits for 02-03 trucks but not 04 and newer. Does anyone know if the 02-03 kit would work? I reached out to fine lines / sstubes.com and they didn’t think their 02-03 kit would work on an 04 because the evap and emissions systems allegedly were changed in 04. Any insight would be helpful. Thanks
Click to expand...
So if I can get someone with HP tuner to delete the rear tank I shouldn't have a problem? It should read right?
 
8100Avy said:
I can provide some first hand experience with how the fuel gauge in the dash reads and how large each tank is. I recently bought an 04’ 2500 and the neck of the rear fuel tank was cracked. My first fuel up attempt lead to gasoline just dumping on the ground instead of going into the truck. I ended up cutting the hose leading to that tank and plugging it off so I could at least put gas in the truck. So now I just have the main/front tank operational only.

When I fill the truck up all the way the fuel gauge in the dash only reads 3/4. To verify the main tank was actually filling 100% I fueled up until gas overflowed out of the filler neck. The truck definitely calculates how much fuel is in each tank and then displays a single reading on the dash. Furthermore, I have HPtuners and licensed the truck. The PCM file shows the main tank is 25 gallons and the rear tank is 13 (38 total). Additionally, 25 is 65% of 38 which closely matched my dash read out. Even further I “tuned out”/deleted my rear fuel tank in the PCM file to see if I could get my fuel gauge to read correctly for only using the main tank. I was successful and now when I gas up I have an accurate fuel reading. I usually fill up at a 1/2 tank and I routinely put in 12-13 gallons.

Summary: fuel gauge takes a reading from both tanks and a single reading is calculated by the PCM. The main tank appears to be 25 gallons and rear appears to be 13 gallons.

I will be attempting to replace my fuel lines and the rear tank in the next few days. I’ve found full replacement fuel line kits for 02-03 trucks but not 04 and newer. Does anyone know if the 02-03 kit would work? I reached out to fine lines / sstubes.com and they didn’t think their 02-03 kit would work on an 04 because the evap and emissions systems allegedly were changed in 04. Any insight would be helpful. Thanks
Click to expand...
2004 has a return less fuel system. MAY be the same fuel lines but just missing the return line.

I need to dig into mine. When I fill the tank I get a gas smell until I use up enough gas so it doesn't. It only happens when I have a full tank.
 
Sstevieboy0208 said:
So if I can get someone with HP tuner to delete the rear tank I shouldn't have a problem? It should read right?
Click to expand...
If you have a similar issue as me and you’re not using the rear tank, HPtuners can get your dash to read just the main tank correctly. It was a simple fix and you don’t need to be a tuner to do it. Instead of paying a couple hundred bucks for someone to do it you could purchase an HPtuners device and license the truck yourself if you’re up for it. HPtuners is a good scan tool to diagnose any future problems, can delete/erase nonsense check engine lights, etc. I also use mine for any used cars the family purchases so I can see the DTC history of the car. Just something to consider. I’d be willing to assist you if needed.

To delete the rear tank with HPtuners….Under the main fuel tab, you can find values for both tanks as well as total combined volume. I changed the rear tank volume to zero in all fields and changed the combined volume to the same value as the main tank. I did not modify the main tank values. The truck out no longer accounts for the rear tank and operates as if the main tank is the only fuel tank. It took me a few mouse clicks and 5 minutes tops.
 
redheadedrod said:
2004 has a return less fuel system. MAY be the same fuel lines but just missing the return line.

I need to dig into mine. When I fill the tank I get a gas smell until I use up enough gas so it doesn't. It only happens when I have a full tank.
Click to expand...
Appreciate the insight. I’ll try to call some other businesses today and see if I can find a solution. Good luck with your project.
 
8100Avy said:
If you have a similar issue as me and you’re not using the rear tank, HPtuners can get your dash to read just the main tank correctly. It was a simple fix and you don’t need to be a tuner to do it. Instead of paying a couple hundred bucks for someone to do it you could purchase an HPtuners device and license the truck yourself if you’re up for it. HPtuners is a good scan tool to diagnose any future problems, can delete/erase nonsense check engine lights, etc. I also use mine for any used cars the family purchases so I can see the DTC history of the car. Just something to consider. I’d be willing to assist you if needed.

To delete the rear tank with HPtuners….Under the main fuel tab, you can find values for both tanks as well as total combined volume. I changed the rear tank volume to zero in all fields and changed the combined volume to the same value as the main tank. I did not modify the main tank values. The truck out no longer accounts for the rear tank and operates as if the main tank is the only fuel tank. It took me a few mouse clicks and 5 minutes tops.
Click to expand...
My issue is the rear pump not reading right and throwing a code for it. Where are you located
 
Why delete it you can buy a new pump for around $60, it comes with a new fuel level sender..
Just drop the tank and replace it... What am I missing? No skills to do it?
 
Randy said:
Why delete it you can buy a new pump for around $60, it comes with a new fuel level sender..
Just drop the tank and replace it... What am I missing? No skills to do it?
Click to expand...
Where did you find it for 60 brother ? I can actually do it myself
 
ebay.. you'll have to verify the PN.. If I was closer, I'd help you..

www.ebay.com

04 chevy avalanche 2500 rear fuel pump for sale | eBay

Get the best deals for 04 chevy avalanche 2500 rear fuel pump at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!
www.ebay.com
 
Reno Nevada...
 
Randy said:
Reno Nevada...
Click to expand...
A little far for me. Anyway I looked up the code I'm getting and found a service bulletin about that code with a hose that balances both tanks and looking under my truck found a skinny hose coming from the rear tank just hanging there. So tomorrow I'm going to look into it and will keep you guys posted.
 
redheadedrod said:
2004 has a return less fuel system. MAY be the same fuel lines but just missing the return line.

I need to dig into mine. When I fill the tank I get a gas smell until I use up enough gas so it doesn't. It only happens when I have a full tank.
Click to expand...
My 04’ 2500 did in fact have a return less setup. I only had 2 metal lines (supply and vapor/purge) running from the motor to the main tank. The rest of the tubing for the evap system and the tubing that connects the gas tanks together were rubber/nylon or a similar material. I only replaced the metal lines.

I used the linestogo.com fuel line kit that included both metal lines and they were correct. Both lines were 3/8”. This is different than the inlinetube.com lines I found. I don’t think inlinetubes.com is aware the 04’s switched to a return less setup. Their lines are sold individually and are labeled for years 00-04. Then for the years 05 and 06 they don’t appear to have fuel lines for 8.1 equipped vehicles. I’m guessing the “dual tank” fuel lines they offer are only appropriate for 02’-03’ 2500 Avalanches. The sizes for the 00-04 labeled lines inlinetubes.com offers are: The vapor line is 1/4, the supply line is 3/8 and the return is 5/16. Inline tubes.com lines are $220 each and have a 4 week turn around time as well. I paid about $250 with tax for the linestogo.com kit and it included free 1 day shipping.

Additionally sstubes.com only sells a fuel lines for 02’-03’ Avalanches (they offer a stainless steel kit for about $500). They do not stock fuel lines for 04-06, however, they did say if you ship your fuel lines to them they can build a new set from your old lines. I was told they could build 2 new lines in stainless steel for $250-$300.

Summary: If you have an Avalanche 2500 model years 04-06 you’re very limited on fuel line options. I only found one company (linestogo.com) that had the correct lines in stock. The linestogo.com lines are galfan coated steel and not stainless steel. I had my lines sprayed with an undercoat when they were installed. The shop said it took them nearly a full day to install the 2 lines FYI

Another fun fact: if you’re looking for acquire a replacement fuel tank from a junkyard…UPS does not ship items that previously contained a fluid. So you have to get the tank freighted on a semi truck as your shipment which is at least $250 from what I was told. I got lucky and found a tank within driving distance.
 
You must log in or register to reply here.
Back
Top