Gas Gauge Issue

[JMM1997]

I recently purchased a 1997 Tahoe that is in excellent condition. The one known issue it had was a gas gauge that would bounce around erratically and get worse as the tank has less gas in it. I have had the fuel pump and sending unit replaced as well as all the wiring checked. Everything seems good there.

I have had the cluster out and replaced the stepper with no luck. Finally after this last trip to the garage and they could find nothing, I replaced the entire cluster. No change whatsoever. I am totally banging my head. In my troubleshooting, I had a meter on the gas gauge pin on the cluster bulkhead measuring resistance and it is erratic when you lurch or move the truck around. Two different mechanics are insistent that this is not a fuel pump or sending unit issue, but I tend to disagree.

When the tank is full, the gauge is rock solid. When it drops to around 3/4 tank is when the erratic behavior starts and it just gets worse as you burn off gas. Anyone ever see anything like this? This is not a complex design so it is so frustrating that no one can find an issue.

 

[Marky Dissod]

Willing to bet money I don't have that the problem is by / near the floater, closer to the fuel tank.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

What brand of fuel pump and sending unit did you install?

 

[Fless]

Agree with @Marky Dissod that the float might be getting caught on something in the tank (pump mis-clocked if that's even possible, or wrong pump, bent float arm, compromised float, etc.) or intermittent resistance in the contacts that the float controls. In that case you may want to pull the pump and measure that resistance over several sweeps of the float, and inspect for interference inside the tank.

The resistance sweep is best done with an analog ohm meter or a scope. Digital displays may not show dropouts our anomalies.

 

[strutaeng]

It's called the "hummingbird fuel guage".

My 00 K3500 beater has that, but i've never messed with it. The OBS cluster guages are horribly inaccurate (in my case, speedo, temperature are way off, and I also have that hummingbird fuel guage and the level sometime goes from 3/4 to 1/4 within a few minutes, LOL). But here's how go about trying to fix it: https://www.gmt400.com/threads/how-to-fix-bouncy-hummingbird-fuel-gauge-needle.15139/page-7

 

[Eman85]

From your diagnosis I'd say it's time to drop the tank and have a look see. I'm old and have CRS but I do remember a tank I dropped had a plastic baffle come loose in the tank, can't remember if it was a Tahoe or a PU. I can't remember if those tanks have a baffle, do you know if the tank has been replaced? Either way I'd drop the tank and at the least use the sending unit as your tester and move the float slowly and have someone watch the gauge. Be sure to check the ground wire attachment. Last one of those I did I replaced the fuel line with plastic line as they tend to rust and the rubber lines at the sending unit are a pain if rusty.
This is why they went to buffers on the fuel gauge, don't think 97 had one but check the wiring schematic.

 

[exp500]

Simple check/test is another ground wire to pump/guage. Or a cleanup of original.

 

[LsHart]

I've always known that when the gauge starts going crazy, update the fuel sending unit. In those years.