At a loss with Fuel Gauge

[CBenZ71]

Hey everyone, I am stuck trying to fix my fuel gauge in my '99 K2500 7.4l.
Background: It has a slight hummingbird issue with it, but more important it only reads 3/4 at full. This has happened recently because it used to go to full. Last weekend I dropped the tank and replaced the pump and sending unit, checked the wiring, all good. Gauge did not improve at all.
This weekend, I went out and got a new cluster from a friend that is verified in good condition, and plugged it in and the gauge is doing the exact same as the original cluster...
I'm lost now. What else can I check? Is there another ground somewhere I can check? A voltage regulator that could be bad?
Anything you've got is greatly appreciated.

 

[delta_p]

There might be a problem with the wire that goes from the fuel gage pin at the cluster to the sender. That wire attaches to the sender then to ground. Usually when the sender registers 0 ohms, the gage reads empty and when the sender reads 90 ohms, the gage reads full. If the wire from the cluster to the sender has a short in it, but not to ground, but through some path of resistance then the gage will be off. Like maybe at the sender connector itself.

To check the cluster ground you could jump the ground pin on the cluster through a fused wire to a known good ground with the cluster connector plugged in. Then you would be more confident it's either the sender wire or the sender connector, given the gage itself is ok not sticking.

 

[AK49BWL]

98+ the sender runs to the PCM, the PCM then provides the fuel gauge signal to the cluster. That's why it does the hummingbird thing - you're literally seeing the Pulse-Width Modulated signal. Ground at the fuel sending unit is suspect, but since the PCM is in control of the gauge, it could be a number of different problems.

 

[CBenZ71]

98+ the sender runs to the PCM, the PCM then provides the fuel gauge signal to the cluster. That's why it does the hummingbird thing - you're literally seeing the Pulse-Width Modulated signal. Ground at the fuel sending unit is suspect, but since the PCM is in control of the gauge, it could be a number of different problems.

Ahh yes!! Thank you for reminding me. So I attached the 0411 wiring guide and Highlighted the three wires that may have something to do with this. Is is possible the fuel gauge got programmed incorrectly when the shop tuned my 0411?

You must be registered for see images attach

 

[AK49BWL]

LOL. You didn't mention being 0411 swapped

I actually have a thread about this. Depending on where the source tune came from, there's a good chance the calibration is wrong.

https://www.gmt400.com/threads/hooking-up-97-fuel-gauge-to-12200411-pcm.36855/

 

[CBenZ71]

LOL. You didn't mention being 0411 swapped

I actually have a thread about this. Depending on where the source tune came from, there's a good chance the calibration is wrong.

https://www.gmt400.com/threads/hooking-up-97-fuel-gauge-to-12200411-pcm.36855/

Thank you!! Yes I will almost guarantee that this is the issue. Now looking back on it, happened right after the swap!! I will call the shop and show them your table. Thanks again!!