1973-1991 Dual fuel tank systems theory of operation

[gmachinz]

A lot of times its just the simple things. The fuel sender has an arm attached to the float which makes contact with the resistance board as full levels move up and down. Throughout the full motion you get anywhere from 0-96 ohms on average. Most of the time if you have more than 50K miles on a stock sending unit, that resistance board will be worn enough that the gauge is off noticeably. Most worn units I’ve seen is from half tank and less-most people dont keep their tanks topped off while never dipping below a half tank for example. The high mileage resistance boards are always worn out at half tank and less which is why the gauge reads fine on full but near a half tank the gauge tends to wander all over the place. Quality of the sending units are worse with offshore replacements than GM or NOS ones as well.