Do we even know what type of meter is involved?

Good point! I'm more familiar with old style fuel gauges but I've just tested the gauge taken from a 2005 Mazda MX-5 (Miata) and it has coils which look like it may be an air core meter, a resistance of 120R and two series resistors which each are 65R and 55R meaning the coil resistance is low.

I connected 12V across it and it took 80 seconds to go from E to F. I removed the power and the needle stayed at full. So I reversed the polarity and it took around 80 seconds to go back to Empty. It does the same but slower if I use 3V instead of 12V. I'm wondering if the electronics simply drives it with a positive voltage then reverses polarity and the expected position is determined by the ratio of times spent positive and negative? Maybe I'll try this with an Arduino although an additional resistor would be necessary to bring the current down to 20mA, or an H bridge.

Because it stays in position when power is removed (or even shorted across the inputs) I'm thinking it can respond very slowly because unless someone has syphoned off fuel it will start in the correct position next time the car is started, but how does the sensor (whatever it is) know where the needle is pointing?

But I'm stumped, how does this meter work?

 

But I'm stumped, how does this meter work?

Stepper motor?

 

Stepper motor?

Nice thought, got me thinking. The resistance between the two terminals is 122R, the resistance from one terminal to the ground terminal is 220R and the other is 98R so I suspect it's an air-core meter where different voltages applied to the two terminals would determine the pointer direction and it maybe has some kind of dashpot inside so it stays wherever it is when there is no power. Or maybe the just the same voltage applied to both terminals? I need to get my head around the probable schematic and try it....

Given the TS was seeing a similar problem maybe his gauge is the same technology.

 

But I'm stumped, how does this meter work?

Like a stepper motor.
It has two coils at right angles, the magnetic field generated by the two perpendicular coils sets the angle of the pointer.

 

It has two coils at right angles, the magnetic field generated by the two perpendicular coils sets the angle of the pointer.

Understood. Ages ago I used an arduino to drive an MX5 tachometer, I'll dig out that sketch and give it go. Clearly, it doesn't need to rotate more than about 90 degrees whilst the tacho needed 270 degrees

 

Understood. Ages ago I used an arduino to drive an MX5 tachometer, I'll dig out that sketch and give it go. Clearly, it doesn't need to rotate more than about 90 degrees whilst the tacho needed 270 degrees

The tacho needs to respond a tad quicker as well!
Tachos are generally moving coil.

 

Well, we do have one poster who says he tried that and it was unworkable. I have no experience with them, so the best I can do is approximate what the resistive sensor was doing. I would be nice to know at least the range of resistance of the sensor and the range of currents as it varies. Someone said 10s of milliamps, so we know the order of magnitude.

My impression, after reading the poster's description, is that only different frequencies were tried, assuming that it was pulse width and not duty cycle that had the effect. Insufficient knowledge is often rather dangerous.
At least some of the gages in the past were bimetal, heated devices . If it is a dual coil gage it is not at all like a stepper motor gage, which is far to expensive for an automotive application.

 

My impression, after reading the poster's description, is that only different frequencies were tried, assuming that it was pulse width and not duty cycle that had the effect. Insufficient knowledge is often rather dangerous.
At least some of the gages in the past were bimetal, heated devices . If it is a dual coil gage it is not at all like a stepper motor gage, which is far to expensive for an automotive application.

And I replied stating that I had tried both frequencies and duty cycle. I know perfectly well how a PWM works as I have used it on numerous occasions to power RGB LEDs to change colors.

It may have very well been the gauge I tried was junk and I should have just not responded in the first place. It was out of a 76 Ford truck that the original owner had removed the fan shroud, overheated the engine, and blew both head gaskets. The only electrical wiring in the truck that worked was between the ignition and the Duraspark system. For some stupid reason I thought I needed another project (money pit).

 

OK! That was not clear to me from the post.