midnightleadfoot

Any idea what would cause this..
Sometimes when I start the car it will peg the gauge full, Then after driving some it will read correctly.. Sometimes it won't do it..


No idea if what could be causing this, I'd think if the sender wire was shorting it do it randomly while you drive, it is only after cranking/starting, and only some of the time..
Anyone want to throw a dart at what it might be?

jaunty75

You have an intermittent ground problem. Check the wire from the sending unit to ground. You'll have to crawl under the car to find it. Make sure it is securely attached and that the attachment point is free of rust.

A pegged-to-full gauge means an open circuit (infinite resistance). If the ground is good and the problem persists, you'll have to do some troubleshooting to locate the point where there is an intermittent break in the wiring.

Fun71

My 71 and the 70 before it did a similar thing. I traced it to the brown sending unit wire that runs through the trunk, out a grommet above the license plate, and to the fuel tank sending unit. On the 70, the push-on bullet style connector was loose on the sending unit stud so I simply crimped it slightly with pliers and that solved the problem. On the 71, I am too old and lazy to drop the tank, so when it happens I reach under the bumper, grab the wire, and tug on it until the gauge starts reading correctly. it will work until I hit a bump then the needle goes back to pointing at the HOT light, then next bump it starts swings back to where it should be.

midnightleadfoot

If it did it randomly I could see it, but it can read correctly when you park it, and without moving the car, start it and it's pegged..
I guess closing the door could move the wire to the short, but
I'll trace the sender wire.. and see if it is grounding to the body somewhere.

Fun71

Yep, mine does that sometimes.

oldcutlass

As the others stated, you probably have an intermittent or corroded connection that's leading to an open circuit. Your going to have to troubleshoot by making sure all connections from the fuel tank to the gauge are clean and tight.