I am going to test my fuel gauge, due to it is reading incorrectly (sits near empty when tank is full). What is the best way to do this? On the back og the gauge, there are 2 studs next to each other, and one stud on top. I am thinking use an ohmeter to test resistence. If the gauge is full, it should read 90 ohms, move the gauge to empty, it should read 0 ohms. Is this correct, and which studs on the back of the gauge should I be testing? Thanks for any and all help!

 

Moving the gauge will not change the resistance of anything. It is the sender in the gas tank that has a variable resistance. The gauge just consists of a couple electromagnetic coils that move the needle around depending on how much current passes through each one. That current is controlled by the resistance of the sender.

None of that really answered your question though... I would say that as with any coil it is probably good as long as its resistance is not too low and not too high. I.E. less than infinite and more than 0. On a gauge I have sitting around I measured ~40 ohms between the two terminals that are connected by the white and gray calibrating resistor, and either ~140 or ~90 ohms between either of those two and the third one. I wouldn't say that your gauge should match those values, due to manufacturing variances and changes over the years.

 

I tested 80 ohms between the two terminals with the calibrating resistor, and 100ohms or 180 ohms between either of those two and the third one.

 

Based on those numbers and how the ratios between them are reasonably close to what they are on mine, I'd probably say that your gauge is OK.

 

hook a variable resistor in line with it (i.e. a dash light dimmer switch) put power to it and play with the resistor. if ur gauge moves then its most likely fine and its ur sending unit.

 

oh ya dont forget to provide a ground for it too (ive seen people forget to do that)

 

Be careful when bench-testing gauges. I don't know about thirdgens, but in my experience (mostly with older cars) I learned that typical dash gauges are powered by a maximum of about 3V DC. One trick that we used to use to test them was to connect a 1.5V flashlight battery across the terminals. If we got a reading somewhere between 1/3 and 2/3 of the indication range, the gauge was considered OK. Testing a 3V gauge with a 12V power source may lead to undesired results.

Most of the time, when a fuel gauge does not read correctly, it is because the sender in the tank has failed. This happens because the sender is a variable resistor that is mechanically operated by a float in the tank. Sometimes the float fails, and other times the variable resistor just wears out.

 

I know its not the sending unit, I replaced it 2 weeks ago when I installed a new fuel pump. I did test it before installing, and it registered 90 ohms at full, 0 at empty (so it works properly). The gauge in the dash still is not reading correct, so now I trying to test the gauge. Thanks for the replies guys, keep your ideas comming!