Originally Posted by tdog114
my 2001 jimmy 4dr 4x4 i had to put a new fuel pump on 6mth ago now the fuel gauge started to give me problems, it stays on empty. in this model the sender units and fuel pump is all in one.
so i check out the wire to the sender unit and tested the purple wire which i,m told goes to the fuel level,
should there be power to the purple wire to the unit or not?
You can test the sending unit by removing the wire attached to the sending unit at the tank and ground or touch to the tank itself. If the needle on the gauge goes to full, the sending unit is registering properly. If it does not move it could also indicate the wire has been severed between the tank and the gauge. A fuel gauge reading of full generally indicates a problem with the tank unit, not the wiring.
Resistance in the sending unit decreases as the fuel level drops, and increases and the level goes up. When the tank is empty, the sending unit reads about zero ohms, and when the tank is full it reads about 90 ohms. Gauge operation is also the same with maximum needle deflection corresponding to minimum resistance in the sending unit. In this case, maximum deflection is required to move the needle all the way over to the empty mark.
A short in the sending unit or wiring on a GM system would cause the fuel gauge to read empty, therefore, while an open in the sending unit circuit would make the gauge read full.
If the fuel gauge does not change (always reads the same, always reads empty or full), or behaves erratically, the list of possible causes include a defective voltage supply to the gauge (instrument voltage regulator), a bad gauge, a defective sending unit, a wiring problem between the gauge and sending unit, or a poor ground connection.
Good luck and keep us posted.