Fuel level gauge goes UP not down?
12-29-2017, 11:10 AM
#21
Le Mans Master
Back in the day we had analog fuel gauges where more current thru it meant more deflection of the needle. Maximum current was a full indication. The sending unit was set up so when the tank was full and the float was at the top, there was minimum resistance from the variable resistance unit (rheostat or potentiometer depending how its wired). Zero resistance meant maximum current for the fuel gauge and a full indication.
With a empty tank the sending unit had more or maximum resistance so minimum current for the fuel gauge which gave an indication of lower fuel or empty.
In today's world of digital electronics and digital indicators, you can invert digital logic and use it the way you want to fit your needs. So in the corvette GM made the decision to give a full tank indication using maximum resistance. This is the reverse of old school operation and just decided to do it that way for reasons we don’t know.
Here is an interesting piece of information I have had personal experience with which makes no sense and probably not known. At the senders position of full the resistance should be about 110 ohms (+/- 10 ohms) and the fuel gauge should read full. But if the fuel sending unit is old or defective (dead spots) where the resistance goes way high above the 110 ohms, you would think it would still read full but it does not. It reads anywhere on the fuel gauge and is a meaningless indication. The digital circuits does not like to see a high resistance and then just goes off into left field to indicate anything.
If you missed it, read my post #8 for specific details.
With a empty tank the sending unit had more or maximum resistance so minimum current for the fuel gauge which gave an indication of lower fuel or empty.
In today's world of digital electronics and digital indicators, you can invert digital logic and use it the way you want to fit your needs. So in the corvette GM made the decision to give a full tank indication using maximum resistance. This is the reverse of old school operation and just decided to do it that way for reasons we don’t know.
Here is an interesting piece of information I have had personal experience with which makes no sense and probably not known. At the senders position of full the resistance should be about 110 ohms (+/- 10 ohms) and the fuel gauge should read full. But if the fuel sending unit is old or defective (dead spots) where the resistance goes way high above the 110 ohms, you would think it would still read full but it does not. It reads anywhere on the fuel gauge and is a meaningless indication. The digital circuits does not like to see a high resistance and then just goes off into left field to indicate anything.
If you missed it, read my post #8 for specific details.
