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2500 Fuel System Question

M

Meatsaw

Full Member
Joined
Nov 28, 2020
Messages
38
So I am having issue with fuel level sensor in my 05 2500. 100k miles, great shape original owner. It is not showing full when full, range calculation is inconsistent. Dash cluster has been rebuilt with new stepper motors. I am considering changing out the entire fuel pump/sender assembly due to mileage anyway. A couple of questions:
1-Is sensing only done at the main tank?
2-Are both tanks pumps running high pressure?
I am the type that changes thing before you have trouble, but kinds hoping I don't need to do both pump assembly's to get there.
 
I would try running a couple of tanks of a good fuel system cleaner before swapping parts, it's not uncommon for the fuel level sensor to get hung up due to deposits on the on the variable resistor where the wiper makes contact.

This is how I understand the 2500 Fuel system on my 2002 2500, your 2005 2500 may be different.

When you fill up the fuel goes down the fill tube to a Tee at the top of the rear tank and when that's full the fuel goes to the main tank. When the tank hits a certain level, the pump in the rear tank moves the fuel to the main tank. So, unless you're having trouble with short fill ups or all of a sudden, you're on empty sooner than normal it's probably a sticky level sensor. The rear pump rarely has problems, I don't remember anyone here with a 2500 ever having problems with the rear pump, someone may jump in and tell us different.

If you still need to replace the pump you only need to worry about the main tank, it supplies the high pressure to the rails (approx. 58psi) there are many threads here on changing fuel pumps by dropping the tank and also how to put in an access panel under the rear passenger seat to allow easy and quick access to change the pump. Dealers have been known to charge anywhere from $750 to $1,500 to change them. If your mechanically inclined, you can pick up just the pump for under $50 or a complete module for $75 to $250 depending on if it's aftermarket or OEM.

Good luck
 

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Randy said:
I would try running a couple of tanks of a good fuel system cleaner before swapping parts, it's not uncommon for the fuel level sensor to get hung up due to deposits on the on the variable resistor where the wiper makes contact.

This is how I understand the 2500 Fuel system on my 2002 2500, your 2005 2500 may be different.

When you fill up the fuel goes down the fill tube to a Tee at the top of the rear tank and when that's full the fuel goes to the main tank. When the tank hits a certain level, the pump in the rear tank moves the fuel to the main tank. So, unless you're having trouble with short fill ups or all of a sudden, you're on empty sooner than normal it's probably a sticky level sensor. The rear pump rarely has problems, I don't remember anyone here with a 2500 ever having problems with the rear pump, someone may jump in and tell us different.

If you still need to replace the pump you only need to worry about the main tank, it supplies the high pressure to the rails (approx. 58psi) there are many threads here on changing fuel pumps by dropping the tank and also how to put in an access panel under the rear passenger seat to allow easy and quick access to change the pump. Dealers have been known to charge anywhere from $750 to $1,500 to change them. If your mechanically inclined, you can pick up just the pump for under $50 or a complete module for $75 to $250 depending on if it's aftermarket or OEM.

Good luck
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Man thanks so much for the info! I will try some cleaner for now, but I think a front pump is prolly a good idea. I had it changed under warranty at around 10k, I kinda feel like these things are on borrowed time anywhere over 80k, at least her in the Vegas heat. I will look into how tough it is to locate and cut an access panel. It seems like it would be pretty hard to do without hacking it up but man it would be nice.
 
Take a look here...


How to change the Fuel Pump.

OK, I search a bit before I started this and didn't really find any how to info. Alaska AV posted up some pictures once, but forgot the how to part. :E: Lets see how this thread works out. First, here is the photo of the AV on the ramps, I also had to use a floor jack to lift the rear a...
www.chevyavalanchefanclub.com www.chevyavalanchefanclub.com
 
Randy said:
Take a look here...


How to change the Fuel Pump.

OK, I search a bit before I started this and didn't really find any how to info. Alaska AV posted up some pictures once, but forgot the how to part. :E: Lets see how this thread works out. First, here is the photo of the AV on the ramps, I also had to use a floor jack to lift the rear a...
www.chevyavalanchefanclub.com www.chevyavalanchefanclub.com
Click to expand...
Thanks a bunch! I think I may do the floor cut method. I saw a drawing you did back then, you still think those are the best measurements?
 
I did not put any measurements in my post on page 7 other that the size of the opening because things could be different from year to year on 2500's and definitely different from a 1500. I just said to look between the frame and floor, you can see the top of the pump module, measure and then transfer the measurement to the inside. I used a hole saw and metal snips to make my cuts not a Sawzall or cut off wheel which to me can throw a lot of sparks. Also, I slid a piece of cardboard between the top of the pump/fuel lines when I used the hole saw in the four corners so if there were any sparks, they would not fall on top of the pump module and a little more protection for the wires and hoses. Some have had the top of the pump module and/or lines rusted out and leaking fuel so another reason to keep the sparks to a minimum.

If you look at the opening I cut it is slightly offset from the top because if I would have centered the opening above the pump I would have had to cut though a double layer of sheet metal that looked to be part of a bracket for mounting, I don't remember exactly it's been more than 10 years. Also I made a panel to cover the opening out of a piece of floor from a junk yard Avalanche. I didn't want there to be chance of fumes or water coming into the passenger area.
 
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When I changed my fuel pump (with a lifetime one) I removed the rear seat and cut a square opening in the floor to gain access. It wasn't a butcher job as I did it cleanly and precisely. I bent the floorpan cut piece back down and pop-rivited a piece of aluminum over the hole. Caulked as well.
 
I'm not sure about cutting an access hole in floor since it may allow easy access to pump but you can't inspect fuel lines for wear and tear and if a line breaks you would still need to drop tank to fix. Just my .02 but i would just do it the recommended way and drop the tank so you can thoroughly inspect fuel and electrical lines etc. for corrosion in these older vehicles.
 
Vaeagleav said:
I'm not sure about cutting an access hole in floor since it may allow easy access to pump but you can't inspect fuel lines for wear and tear and if a line breaks you would still need to drop tank to fix. Just my .02 but i would just do it the recommended way and drop the tank so you can thoroughly inspect fuel and electrical lines etc. for corrosion in these older vehicles.
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I have to agree with this, especially if you live in the rust belt. I had to drop the tank on my Z-71 a couple years ago. It really wasn't that bad. I'm glad I dropped it vs. doing the hatch because I found I had to replace the lines on top in addition to just the fuel pump.
 
I don't live in the rust belt so no worriers, this is what mine looked like when I replaced the fuel pump.. I little paint and it was good as new..
 

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Randy said:
I don't live in the rust belt so no worriers, this is what mine looked like when I replaced the fuel pump.. I little paint and it was good as new..
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I'm so jealous....

sincerely, guy with rust breaking through on both rear quarters, under one door and on another... And suspension parts that fuse together...
 
I feel for you, living on the West coast vehicles last forever. My AV is 20+ years old with almost zero rust, just some surface rust on the rear end housing. I think the car manufactures should add an option for vehicles and can be ordered with extra protection. It would cost more but it could mean your 5-year-old vehicle wouldn't have holes rusting through. But then they wouldn't sell as many cars.
 
BainMan said:
I'm so jealous....

sincerely, guy with rust breaking through on both rear quarters, under one door and on another... And suspension parts that fuse together...
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I feel your pain man. I need to save some serious coin for a major rust repair and paint.
 
Or in the immortal words of Sam Kinison, you could, MOOOOOOVE..
 
Randy said:
Or in the immortal words of Sam Kinison, you could, MOOOOOOVE..
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Nah, I love the cold and the snow. I just finished cutting the grass for the first time this season and I would much rather shovel snow. What we need is for all the pansies who are afraid of the snow to move and let us snow living folk get back to simply plowing and dropping sand instead of salt and brine.😁🛷🏒⛸️❄️
 
I wonder how long it will take for the ambulance chasing lawyers to figure out they could sue the states for "destroying their client's vehicle with chemicals". Boy that would sure clog up the court system! :)
 
Meatsaw said:
Man thanks so much for the info! I will try some cleaner for now, but I think a front pump is prolly a good idea. I had it changed under warranty at around 10k, I kinda feel like these things are on borrowed time anywhere over 80k, at least her in the Vegas heat. I will look into how tough it is to locate and cut an access panel. It seems like it would be pretty hard to do without hacking it up but man it would be nice.
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did the cleaner work for you ?
i am having the same exact issue on my 2500 and not looking forward to replacing the pump , in my case i am getting a code every once in a while for insufficient fuel pressure , P1172
 
You have hit a GM specific code, that code for the rear fuel pump. How it works is when you reach a certain fuel level the PCM turns on the rear fuel pump to transfer the fuel out of the rear tank to the front fuel tank. If it does not sense the level in the front tank go up it set that code,

check your fuel pressure at the rail it should be around 45+ ish, it's probably time to change your fuel filter also.
 
MS03 2500 said:
You have hit a GM specific code, that code for the rear fuel pump. How it works is when you reach a certain fuel level the PCM turns on the rear fuel pump to transfer the fuel out of the rear tank to the front fuel tank. If it does not sense the level in the front tank go up it set that code,

check your fuel pressure at the rail it should be around 45+ ish, it's probably time to change your fuel filter also.
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So fuel pump and the filter ? It doesn't throw that code all the time. It's every once in a while. And also did you drop the tank or cut an access hole. Of so can you send me the measurements and how far from the door and all of that ? I would truly appreciate it
 
Remember, 2500s have 2 gas tanks and pumps the second is above the spare tire so no need to cut a hole, it only holds 6 gallons.
But yeah I did cut a hole around 10 years ago for changing the front pump but my original pump is still good, I used to travel a lot with it, and it would cost a fortune to pay somebody to change it. Much less find a fuel pump for a 2500.

If you look at the inside of the frame rail in front of the abs module you will see the fuel filter. I'm pretty sure all 2500s had a external fuel filter.
 
MS03 2500 said:
Remember, 2500s have 2 gas tanks and pumps the second is above the spare tire so no need to cut a hole, it only holds 6 gallons.
But yeah I did cut a hole around 10 years ago for changing the front pump but my original pump is still good, I used to travel a lot with it, and it would cost a fortune to pay somebody to change it. Much less find a fuel pump for a 2500.

If you look at the inside of the frame rail in front of the abs module you will see the fuel filter. I'm pretty sure all 2500s had a external fuel filter.
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I will look tomorrow. Thank you for all the help. So the rear tank is easy to drop and replace that pump ? And yes it does have an external fuel filter. And also one more question. If it is the rear pump. Could it cause faulty fuel level reading on the dash ? I truly appreciate all the help. Just don't want to replace only one if I need both.
 
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Sstevieboy0208 said:
I will look tomorrow. Thank you for all the help. So the rear tank is easy to drop and replace that pump ? And yes it does have an external fuel filter. And also one more question. If it is the rear pump. Could it cause faulty fuel level reading on the dash ? I truly appreciate all the help. Just don't want to replace only one if I need both.
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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.
 
Sstevieboy0208 said:
did the cleaner work for you ?
i am having the same exact issue on my 2500 and not looking forward to replacing the pump , in my case i am getting a code every once in a while for insufficient fuel pressure , P1172
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I ended up replacing the main pump. I took it to a buddys house and did it on a lift. Only thing I regret is I forgot to mark a spot from underneath in case I want to cut a hole in the floor in the future. Also FYI sometime prior to 2005, they got rid of the external filter mounted on the frame. The only filter on mine is the one in the tank.
 
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