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Fuel Gauge - new thread

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JPSmit

JPSmit

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Didn't want to hijack the other thread on the gauge running empty. but, this was posted there

<span style="font-style: italic"><span style="font-weight: bold">"First, that gauge has to be grounded or it will always read empty. If it goes to hard full and the tank is not then that suggests a break or bad connection in the wire between the gauge and the sender. A bad ground at the sender will do the same. If it goes to hard empty then that suggests a short in that same wire. I really don't think the lights are related. Be sure you have a green wire to the B post of the gauge and a green/black to the T post. The case must be grounded. If you remove the green/black from the T post and check its resistance, it should be somewhere between 0 (empty) and 70 (full)." </span></span>

I run our of gas when the gauge shows 1/4 tank. it is a new tank and a new gauge (VB) what should I be thinking of doing?
 
If this is for your '76 1500 it will use a different gauge system than the Bugeye in the other thread. The later gauge system was implemented in the early to mid-1960s and is based on resistance heating of a bimetallic element in the gauge. None of the comments in the other thread will apply to your car.

You stated above that you run out of gas at 1/4 tank. I assume since you mentioned no other problems that a full gas tank results in a gauge that shows "full". If that's true, it would appear that you have a gauge calibration issue.

I have not found a definitive web reference for the steps to use when calibrating the bimetallic gauges. At this time all I can say is that on the back of the gauge you will either find two small screwdriver looking slots in small holes... or two screwdriver slots in small holes that are plugged with tiny cork disks. Remove the disks as necessary and you can use those two screwdriver slots to tweak the zero and span of the gauge. To do this you really need to be working on the workbench and you need the sending unit out of the tank... and all wired/powered up so you can make the gauge match the sending unit.

Regularman (a.k.a. Kim) on this forum is the Spridget gauge guy. He may have a procedure for making these adjustments quickly and properly. If he doesn't post to this thread you may want to send him a PM to see what advice he can offer.
 
Check to make sure the voltage stabilizer is pulsing on and off; if it is stuck on, it might be making your gauge read high. A multimeter should show it turning on and off a few times each second. It's on the bulkhead inside and above the glove box, and I believe the output side is the green and purple wire.
 
What is the right output voltage from the stabilizer? It would be a lot easier to check that than the on/off cycles.
 
The nominal output of the stabilizer is 10V but it's an average of 10V since the unit switches on and off. You must use an analog meter to measure it as a digital meter is likely to randomly catch an on or off cycle as it updates its display.

A general second sanity check for the bimetallic gauge system is to look at what the temperature gauge is doing as it is also connected to the voltage stabilizer. If your temp gauge is reading high as well as the fuel, it could be that your stabilizer has failed with its contacts closed OR lost its ground connection. The stabilizer must be grounded through its case to work.
 
You might want to also have a mechanical look at your sender. Some of them have a little metal tab that keeps the slider over against the sender wire wound resistor and if there is wear in there then the slider might be moving back and forth sideways and moving completely off the wire and making the gauge jump back and forth, also some of the replacement senders are way off the resistance they should be at for a given tank level.
 
First off, let me say thanks and that this might be a good winter project. That being said,

Kim, thanks for your advice - it is a brand new sender so I'm hoping it isn't worn.

The gauge does indeed read full when it is full.

The temp gauge (which is mechanical) does not read high - it reads fine. However, it seems to jump occasionally. Everything else works perfectly.

I'll check the stabilizer though likely later as I don't really want to pull the glove box.

I presume if it isn't working I won't do any damage will it?
 
The only thing in my midget that uses the stabilizer is the fuel gauge, the temp is purely a mechanical bourbon tube type. I replaced my stabilizer with a solid state mod diy project that I am sure someone on here has the plans for. For testing purposes you can use batteries to get the 10v.
 
regularman said:
The only thing in my midget that uses the stabilizer is the fuel gauge, the temp is purely a mechanical bourbon tube type. I replaced my stabilizer with a solid state mod diy project that I am sure someone on here has the plans for. For testing purposes you can use batteries to get the 10v.
Click to expand...

Not sure I understand - OK, I'm positive I don't understand - I hook up the fuel gauge to 10v? then it should read accurately?
 
JPSmit said:
regularman said:
The only thing in my midget that uses the stabilizer is the fuel gauge, the temp is purely a mechanical bourbon tube type. I replaced my stabilizer with a solid state mod diy project that I am sure someone on here has the plans for. For testing purposes you can use batteries to get the 10v.
Click to expand...

Not sure I understand - OK, I'm positive I don't understand - I hook up the fuel gauge to 10v? then it should read accurately?
Click to expand...
No, what I meant was that you can use 10v from batteries to test your system without using the stabilizer and then see if it reads accurately. If you have the correct gauge then it was meant to operate off of 10v from the stabilizer, reason being is the generator output was weak with the headlights and heater blower on and the system voltage would drop down low at stop lights and if the gauge was made for 12v then it would not read correctly. The system would almost stay above 10v, so they came up with the stabilizer to keep it at a constant 10v average.
 
The very simplest version of the solid-state stabilizer replacement can be found in this JPG link from my friend Wes.
https://www.adocars.com/elf-ado/elf/elfimages/v-reg.jpg

If you want to try a more packaged arrangement or use components from Radio Shack, you can follow the steps in my PDF.
https://home.mindspring.com/~purlawson/files/SmithsVoltageStabilizer.pdf

If you don't want to make your own (and the chips are available from Mouser.com), Moss now sells solid-state stabilizers for under $20 in both positive and negative ground.

As Kim said, supplying the gauge with 10V directly (instead of off the car's wiring) is a good test to see if the stabilizer is working. As a footnote to this, the project Spitfire I'm working on came to me with a new radiator and electric radiator fans. When I started poking around I found a previous owner "dismounted" the voltage stabilizer so it was hanging by its wires without an earth connection. To them, the car ran hot (hence the new parts). Once the stabilizer got its ground back the gauge indicated the real temperature... about 30% cooler.
 
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