Fuel gauge or sending unit ??

So, I'm trying to get my fuel gauge to operate correctly. I'm working on the 50' Chevy. When I got the car the gauge powered up to a full tank every time regardless of the level in the tank. I traced the wire back to the sending unit and noticed that when the car was converted to 12 volts they used a ceramic voltage reducer. The round one typically used for heater motors. I was told that can damage the gauge. Thinking that was the problem I cut it out and installed a Runtz reducer at the gauge. When I powered it back up the needle went right back to full. Now, the the needle moves down to empty with the amount of ground ohms right? So, anyone have an idea if the motor reducer fried the gauge, or could the sending unit not be operating correctly? Any help would be appreciated before I have to drop the tank. Is there a way to test the sending unit?

 

by your description the voltage reducer was installed in the wire going to the sender...correct? where do you have this runtz installed?

 

It's installed on the positive side. I just checked it.....t reads 7.25 volts when I turn the key.

 

Just took the sending wire off the unit and ground it to the frame with a jumper. When I power it up it reads empty. I cleaned all the connections at the sending unit and hooked it back up and........same thing.....It reads full. I'm guessing I have a bad sending unit, or its stuck or something.

 

Make sure the sender is grounded! There should be a tab for a ground wire on the mounting flange, that needs to go to a good chassis ground.

 

What WALDO53 said...

 

not sure if the 50 is the same as the 54, but i had the same problem as you described . The previous owner had some sort of resistor wired from ignition straight to the gauge....my gauge was working then all of a sudden quit on me and read FULL. on the driver side right below the A pillar there is a connector that leads up the A pillar and back to the sending unit...mine got disconnected.

i know you were saying you took off the sending wire from the "unit" and grounded it ...went to EMPTY . By unit i'm not to sure if you meant from the gauge or from the tank. If it was from the gauge side disregard my post.

 

When you ground the sender wire with the key on I think it should show full.

 

I had that thought. There's no tab on the sending unit flange, but I did run a lead from one of the hold down screws to inside the trunk pan. Still no luck....the needle races up to full as soon as I hit the switch. Doesn't the sending unit ground itself to the tank though?

 

Can't remember on your car but some are isolated from the tank and have to be grounded with a wire.

Now, you said you took the wire off (was this at the sender?) and grounded it and the guage went to empty. O.K. that prooves the guage and all the wiring back to the sender is GOOD, that's exactly what should happen. SO, you've either got a bad sender (went open) or it's stuck on full. Sounds like you've got a good ground so I'm betting it's one of the two things I mentioned. Stay with it, you're getting close.

 

The old GM tanks get the ground thru the tank being held in place with the tanks straps. Unless you put rubber are something between the trunk pan and the tank are the tank and the straps you will have a ground.

 

I had to ground out my 53 chev tank for the gauge to work properly. I had the same problem as you described. My guage kept reading "full" untl I grounded the Tank to the body then worked fine.

 

Your sender is shot, check it with an ohms meter it should run from 0 to 30 more or less empty to full, if the ga goes to full with key on its ok, chevys don't go to full when you run the sender wire to ground.