Gas gage suddenly stopped working?

[tkelley72]

Need some more expertise from the experts please. Got in my car today and noticed that my gas gage has stopped working. It worked fine two days ago. The only thing that I have done is put my "Battery Tender" on the car for a few hours. I did notice while in the initial charging phase that the charger got very hot so I'm wondering if maybe somehow this could have put a load on the system and blown a fuse? Unfortunately, I'm too old and broken to crawl under the dash and be able to see the fuse panel so I'll have to go somewhere and have someone more limber to do it for me. If it is a fuse, can someone tell me the fuse location in the holder and what size it is, physically and amperage wise? If not a fuse, what would the next steps to take? The sending unit was replaced a few years ago so I am assuming that it is still good. Like I said, all was well until I put a charger on the car. Thanks for your help guys.

 

[RD-72]

A good YouTube video by mustang restorations inc.
“Chris the doc ingrassis - fix those faulty classic car gauges”

the video showas how to diagnose your problem (the demo is on an older mustang but the principal is still the same with our years)

if all you other gauges are working properly, my guess is that you might need a new sending unit in your gas tank (Else a bad wire)
I recognize your mobility issues, but at least if you understand what might be your issue, you are better off.

 

[midlife]

No fuses for the dash gauges. Are you out of gas by any chance?

 

[tkelley72]

I do have plenty of gas, at least 1/2 tank as the gage was working up until yesterday and I had put gas in it a couple of days ago. I'll check out the YouTube video, should have done that first. All other gages working fine. Good to know it's not a fuse issue though, don't think I could ever get my old butt under there. Thank you guys, always great input.

 

[tkelley72]

One last question. If it turns out to be a defective sending unit, who sells the most reliable product? The one that's in there is only about 5 years old. Should last longer than that. Thanks again

 

[Paul M]

I do have plenty of gas, at least 1/2 tank as the gage was working up until yesterday and I had put gas in it a couple of days ago. I'll check out the YouTube video, should have done that first. All other gages working fine. Good to know it's not a fuse issue though, don't think I could ever get my old butt under there. Thank you guys, always great input.

You can do a quick gauge check by pulling the wire off the sender and grounding it to a clean metal surface.
Turn the ignition key to the “on” position and watch the fuel gauge. If it moves to the “full” position, then the gauge is working correctly. If it doesn't move, there may be a problem with the gauge or wiring to that point.

 

[rcadd1ct]

One last question. If it turns out to be a defective sending unit, who sells the most reliable product? The one that's in there is only about 5 years old. Should last longer than that. Thanks again

I don’t know if any better than others.

Most likely due to the ethanol in the fuel as they were never designed for it.

 

[midlife]

You can do a quick gauge check by pulling the wire off the sender and grounding it to a clean metal surface.
Turn the ignition key to the “on” position and watch the fuel gauge. If it moves to the “full” position, then the gauge is working correctly. If it doesn't move, there may be a problem with the gauge or wiring to that point.

Better to move the key to ACC. When the key is in RUN or ON position, power is applied to the points and you can burn them up if they are in the right/wrong position. ACC key position provides power to everything ON position does except RUN-only power (e.g. coil, points)

 

[Hemikiller]

I bought a replacement sender from NPD and it's been working well for a couple years now. Can't tell you which of the four senders they offer is the one I bought. You do need to calibrate them before installation.

 

[giantpune]

You do need to calibrate them before installation.

How does one do this? I need to work on diagnosing and fixing one of mine.
When I fill the tank, the needle goes way past F and stays pegged there. Then after I drive through 10 gallons of gas, the needle finally moves down below the F. So the full range of my gas gauge is the other 5 gallons.

 

[73pony]

How does one do this? I need to work on diagnosing and fixing one of mine.
When I fill the tank, the needle goes way past F and stays pegged there. Then after I drive through 10 gallons of gas, the needle finally moves down below the F. So the full range of my gas gauge is the other 5 gallons.

Same here. I figured it was just normal.

 

[Hemikiller]

Procedure is in the shop manual, screenshots below. You'll need a couple resistors to test the guage without pulling the sending unit.



Fuel sending unit test below. If it falls outside of the range, then you bend the arm between the pivot and the stops on the bracket. There's also a spec in the assembly manual where the fuel gauge should read with a specific amount of fuel in the tank.

 

[giantpune]

Procedure is in the shop manual, screenshots below. You'll need a couple resistors to test the guage without pulling the sending unit.

View attachment 81342

Fuel sending unit test below. If it falls outside of the range, then you bend the arm between the pivot and the stops on the bracket. There's also a spec in the assembly manual where the fuel gauge should read with a specific amount of fuel in the tank.

So there is not a calibration procedure? The parts are tested and are either working correctly or they are not. And if they are not, something needs replaced?

 

[midlife]

Fuel sending units can be refurbished and calibrated at: https://desertclassicparts.com/prod...ng-unit-rebuilding-service-send-us-your-core/
I can personally vouch for this guy's work to be excellent. He also has a tool to test your gauges.

 

[Hemikiller]

So there is not a calibration procedure? The parts are tested and are either working correctly or they are not. And if they are not, something needs replaced?

The manual doesn't have a step by step process, but you can infer what needs to be done. Remember that these manuals were written with the dealer service department in mind, where new parts were on the shelf. These were simple yes/no diagnostics. Does the gauge read correctly with the specified resistance? Yes - go to the sending unit. Does the sending unit read correctly - no. Bin it and install a new one.

By moving the float arm through it's range, you can verify that it's within spec. If not, you can tweak the inner portion of the arm to get it within range. The only caveat is you need to record where the float rests at the full and empty positions prior. Once you get the readings in spec, you adjust the outer arm to get the float back to it's original positions.

 

[Paul M]

Better to move the key to ACC. When the key is in RUN or ON position, power is applied to the points and you can burn them up if they are in the right/wrong position. ACC key position provides power to everything ON position does except RUN-only power (e.g. coil, points)

Or worse, forget you have the key on for over 5 min and burn up one of those $100 Pertronix modules. The money I spent on those Pertronix modules on my GTO I could have purchased a new MSD distributor.