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Replacing fuel sender in a '04 Avalanche 1500

BAS-Sr

Full Member
Joined
Sep 11, 2015
Messages
66
Location
Millstone Township, New Jersey
My wife's '04 Avalanche fuel gauge has been whacky for a couple of years, does not show full when the tank is full, only goes up to just below the full line and goes down to completely empty when it has about a 1/4 tank of gas. Was fine when we bought it 13 years ago and my wife just can't tell how to compare MPG and miles driven so she knows how many more miles she can drive!

I have a new GM sending unit, about to change it out, have done this on several other vehicles so I am not a novice! Last one I did on a full size truck was a '97 K-1500 extended cab. Did my '95 Suburban too with the 42 gallon tank. Easiest one was when I swapped the tank in my '87 el Camino puttin a '96 Buick Roadmaster tank in when I changed the motor to FI.

Searched the forum and saw a couple of posts, most interesting one was very well documented about how the guy cut the floor to get to the top of the tank, seemed like a possible way to do this rather than drop the tank? Only issues I had with this was figuring where to cut the floor and getting the sender out with the hole that is cut? When I have done this before always dropped the tank and even then getting the ring out of the top of the tank was a challenge!

Would like some opinions from those of you have done this, pros and cons of cutting the floor versus dropping the tank (obviously as close to empty as possible).

Anyone have or seen any videos (or pic's) on doing this by dropping the tank?
 
You'll get varying responses here. Some will swear by cutting the hole while others prefer to keep the integrity of their floorboard in check. Living in the rust belt, I fall into the latter category. I replaced my fuel pump last year by dropping it. It wasn't really a big deal to so as I didn't have much gas in it and what gas I had I was able to siphon out. My ring was rusted to heck and back and I can't imagine having any luck getting it off in the small confines of a hole in the floor.

As it turned out, my nylon lines needed replacing as well which was much easier with the tank on the ground.
 
Yeah, that pretty much sums it up and looks to be the one I used for the job. He just doesn't have the rust issues I have. I had a devil of a time undoing my nylon lines he shows at the 3:10 mark. I'm not exaggerating, it took me a day and tons of spray to undo them. Had I know I'd have to replace them I would have just snipped them from the get go. Whatever you do, make sure to remove the wires prior to dropping them. You don't want to be like this guy:



I used three ratchet straps to drop mine. You can see in the pictures how rusty mine was. Fuel pump or keep digging?
 
Fuel gauges are not like they used to be. PCM reads signal from fuel sender and interprets - then sends digital data to the instrument cluster where that is decoded and used to run a stepper motor on the fuel gauge.

So is your problem with the fuel sender to PCM side, or is the problem with the instrument cluster to PCM side? I would figure this out before I changed a sending unit. Hint..... a capable (simple) scanner for your Android like Car Diagnostic Pro (used to be Gar Gauge Pro) with the GM Enhanced PID set enabled can monitor fuel level % as determined by the PCM before it sends any digital data to the instrument cluster. See photos below - mine KOEO.

Note that the scanner (PCM reading) matches the actual gauge. If it didn't, then the instrument cluster would be to blame. Stepper motors in instrument cluster are notorious for being off.

Also attached is the factory diagnostic info. A 5.3 in 2002-2007 Avalanche is a L59.
 

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  • 2004FuelLevel.pdf
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  • 2004FuelGaugeSchematic.pdf
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Sorry for the delayed response, power was out since last Tuesday and no internet!

Thanks for the replies, decided to just drop the tank, pretty sure the it is the sender just by the symptoms and that is has progressively gotten worse over time.
 
Replacing the old OEM fuel pump with a new ACDelco unit fixed the issue I was having with an wonky fuel gauge.
 
I replaced the unit on my 2003 Avalanche around 2010. I used the through the floor method. No issues. I sold vehicle in 2018. So 8 years strong. No visible rust issues on panel I cut (I live in New England).
 
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