odd voltage on gauges

Hi, I am having a problem with my fuel and temp gauges. The fuel sender is sending the correct resistance to the gauge but the gauge pegs full. The sender is at 77 ohms which should be empty. The problem is the power strap on the back is reading fluctuating voltage that's all over the place: 2v, 8v, 6v.... and so on(should be 5v). It never gets over about 9v. The temp gauge will not reach past about a fifth of its range(shows very cool even when completely warmed up.) I think the regulator in the fuel gauge is bad, any thoughts? Also, seems like I could just replace the fuel gauge since temp gauge shows all the correct resistances. I'm not quite sure why 4wd says must replace both gauges together. If anyone has any ideas on this I would be thankful. Rob

 

Oh Randy isn't this similar to what you were telling me yesterday?

 

I shake my jeep and listen for the gas level to clank around, thats my gas gauge.

 

first off, get a 18.5 inch piece of broomstick and keep behind your seat so you can tell how much gas you have.

actually the regulator in the fuel guage is a set of points with a heating element wrapped around one arm (much like the vibrator in the old car tube radios). when power is put to the guage, the element heats up and makes the arm of the points (a bi-metal strip) deflect breaking the points. this also breaks contact so the element begins to cool and brings the points back together. this happens several times a second. the net result is a fluctuating voltage that is supposed to average 5 volts.

the guage elements in both the fuel and temp guages use the same type of bi-metal strip with a heating element wrapped around. as they heat up with the changing resistance of the sender the bi-metal arm deflects and moves the needle of the guage. these guages are adjustable on the back with a small screwdriver. they never were intended to give you an accurate temp reading, just give you a norm on the guage so you could tell when things were "not normal". nothing wrong with your guages, you should be happy they move.

I have been working on a solid state regulator conversion for the fuel guage but am having a few difficultys with it.


HTH

 

Ahh, I actually repaired the fuel gauge windings very carefully, however, I had to unwrap about 1.5 turns of the winding to make the connection. I guess that is what is causing the higher voltage swing.

 

that will make some difference, but you should be able to adjust the guage to compensate. it will take a couple of tries but there are 2 small slots in the back of the fuel guage. one adjusts the regulator and the other adjusts the guage it's self. if you remove the face you can tell which one. if you have a way to reproduce the resistance of the sender at different levels and a 12 volt source, you should be able to get it pretty close to accurate.

adjust the regulator so that if fluctuates right around 5 volts give or take. the setup relies on the slow response time of the guage needle to dampen the voltage fluctuations of the regulator.

HTH