So i bought this 91 blazer couple days ago. I turn the key and turn the blazer on and the gas gauge reads past full. Then when i turn the key off if slowly comes down to 3/4 a tank. Does anyone know what is wrong please help me. Thank YOU!

 

nothing should be wrong i dont think as long as it reads right when running i had a 89 ford f-250 that did that but read right when runing

 

Does the gauge work properly from full to empty while the truck is being driven? If so, don't worry about what it does after the key is turned off.

 

It always reads past full when I turn it on and drive it around..

 

I have a similiar trouble. I have an 2001 s10 Blazer. And I ran out of gas on the highway because of this. Decided to drop the tank and pull out the pump and the sensor, I clean the sensor and play a little with the level it registered so I can measure if the resistance changes with the level, it went from 50 to 255 ohms...

I didn't really knew what to do next, so I start reading this forum. I found info about the Black wire with the white stripe that needed to be grounded (mine is indeed grounded).

Then I read about the purple wire, who I understand is the sender of the sensor unit of the gauge... I located the wire in the plug that goes to the pump. But I don't really know where's the other end of this wire. I located 2 wires in the cluster of the Blazer that seems to be connected with black/white wire and with the fuel gauge. The fuel gauge have 3 wires... I think the third one should be conected with the purple one from the tank, but it doesn't seem like it when I tested... So I don't know what to do next...

Note: After I droped the tank the gauge now reads only empty no matter what I do

 

frandcv, Check out the thread linked to below:
98+ Fuel Gauge Diagnosis

 

Thanks! I'll performe all those tests tomorrow and I'll let you know if I manage to find the problem