Fuel Gauge Problem

[Zhmurki]

The fuel gauge on my 91 Mercury Colony Park is acting up. It is probably unrelated, but I first noticed the problem after getting an emissions test. Following the test, the needle would always go to full, regardless of fuel level, once the car was started.

I went to the junk yard last weekend and picked up a sending unit, gauge, and chip (from the back of the speedo), and swapped all of the parts out. The tank was near empty at the time. Once I turned the car on, the needle moved to a quarter tank. I figured I would try filling the tank and see what happens. As soon as I turned the car on, the needle went to empty and the low fuel light came on. As I drove the car, the needle gradually went back up towards a quarter tank (once it passed an eighth of a tank, the indicator light went out).

Today, I decided to swap back to the original sending unit. Now, with an empty tank, the needle moves just past half a tank once the car is turned on.

Any ideas? Any other parts that I have not thought of?

[91waggin]

Sticky float. Use an ohmmeter to check resistance between the terminals on the sending unit. Resistance should be high (~80 ohms) when the tank is full, and low (~1.1 ohms) when the tank is empty. You can even play with the float and watch the gauge move. If the gauge moves properly when you move the float, but misbehaves when in the tank, you can bet that the float is sticky.

[Lincolnmania]

bad float maybe
did you get another sending unit out of a wagon? they are different than sedans

[91waggin]

bad float maybe
did you get another sending unit out of a wagon? they are different than sedans

oooh I had forgotten about that