Fuel Gauge issue...TBI

If you have been keeping up with the Ruby build thread, you know we swapped in a 9C1 digital cluster. Well now the fuel gauge doesn't wanna work right.

Key off the gauge goes to about half. Turn the key on and it drops to Empty. Adding gas didn't seem to help (per my son).
I know the harness plug is by the rear DS bumper and as I'm typing this recall he hit my wife's car with same said bumper. Guess he's checking that first thing....

I was posting to see what kind of voltage I could put on the pin to see if it's a cluster issue or sending unit issue.

On the LT1 cars, unplug the fuel pump harness from the car, then ground the purple wire on the vehicle side of the harness. That should make the gauge go to empty with the key on. Leave the wire alone and it should go to full. Maybe the TBI cars work the same way? Never toyed with them.

The gauge reads resistance. The low end is 0 ohms, and the high end is 95 ohms. You can put a variable resistor (or potentiometer center lead to one end) in series to ground with the lead to the gauge, and vary the position of the pointer by changing the resistance.

thanks guys, gives me a starting point.

Here's what you need to dial in the tank gauge from radio shack. The purple wire runs next to your left foot under the carpet.
Ground one end of the resistor to the chassis. It doesn't matter which end. The middle connection gets tied into the purple wire.
When dialing it in, it is very sensitive to change, and thus easy to dial right past. Make small changes and WAIT SEVERAL SECONDS

Why wait? The circuit is designed to be slow to respond and ignore fast changes like when gas sloshes when going around corners or hitting bumps.


http://www.radioshack.com/product/index.jsp?productId=2062308

I may give that pot a try. When I fill up the gauge reads 125% full and it's about empty at an indicated 1/4 tank.

You can dial it down. Keep in mind it is by far more important that it reads EMPTY accurately than FULL.

Well I took jr's car to the liquor store as my wife parked behind me.
Funny thing about fuel gauges. They tend to move when you put gas in the tank.

He had been telling me it would drop to E when he turned the key on and go back to half when you turned it off. OK, I got in started the car and it stayed on half. Started driving and had to stop short on a yellow (Johnny Law at the intersection) and noticed the fuel gauge dive to quarter then roll back up as I sat there. Johnny left and on the green I punched it. As expected as the fuel slosh back, the gauge pushed up. Mystery solved!

Hooray one less project this weekend. Anyway, I have an extra sending unit in the garage and was gonna plug it in and play with it while he watched the gauge.