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Calibrating My Fuel Gauge #447494
08/23/09 08:52 PM
08/23/09 08:52 PM
Joined: Aug 2009
Posts: 2
North Carolina
6
68HemiRoadrunner Offline OP
member
68HemiRoadrunner  Offline OP
member
6

Joined: Aug 2009
Posts: 2
North Carolina
Hi All, first time posting ...

I just replaced the fuel tank sending unit and now the fuel gauge doesn't seem to be working.

I read on here about calibrating the fuel gauge. I've never done that before. Does anybody know where i can find step-by-step instructions on how to calibrate the fuel gauge?

Paul

Re: Calibrating My Fuel Gauge [Re: 68HemiRoadrunner] #447495
08/23/09 09:04 PM
08/23/09 09:04 PM
Joined: Jan 2003
Posts: 32,883
Grand Prairie,Texas
stumpy Offline
I Win
stumpy  Offline
I Win

Joined: Jan 2003
Posts: 32,883
Grand Prairie,Texas
If it's a stock gauge and sending unit then the most you would have to do is bend the float arm to read right. Do you mean the gauge did work and now it won't? Did you ground the sending unit? Have you checked to see if you have a flashing power source at the sending unit wire?

Re: Calibrating My Fuel Gauge [Re: 68HemiRoadrunner] #447496
08/23/09 09:32 PM
08/23/09 09:32 PM
Joined: Sep 2005
Posts: 12,481
Chino Valley
RodStRace Offline
I Live Here
RodStRace  Offline
I Live Here

Joined: Sep 2005
Posts: 12,481
Chino Valley
Fixing a non-working gauge is different than calibrating one.

To diagnose, determine if there is a problem in front or back.

First, do the other gauges work? If not, check the fuses and the voltage limiter on the back of the cluster. Repair as needed.

If the other gauges work, disconnect the wire from the sending unit. Have a helper turn on the ignition (Run). Touch the end of the connector to a good ground. The helper should see movement of the gauge. The gauge is damped, meaning it doesn't react quickly, but you should not leave the wire touching ground for very long, less than a minute should do.
If the gauge moved, you know that the power to the instrument panel is good, the gauge is good and the wire back to the tank is good.
If only the gas gauge doesn't work, even when the sending unit wire is grounded, it's going to be the gauge or the circuit between there and where you grounded it.


Visually inspect the wire, making sure there are no bare spots or broken areas.
You can also carefully ground the same wire at the back of the cluster. This will be a tight, dark, difficult area, so leave the jumper wire disconnected until it is firmly connected to the right wire ONLY. Then turn on the ignition and ground the wire. If this works, the gauge works and there is a problem in the circuit. If it doesn't, it's probably the gauge.

If grounding the sending unit connector makes the gauge work, but it does not when connected to the sending unit, it's either the sending unit or a poor ground. Using a jumper wire, connect one end to the sending unit, and the other to a good ground. Reconnect the gauge wire, and check the gauge. If this makes it work, the sending unit needs to be grounded. There is a little strap that connects to the metal line on the sending unit and the line on the body, right next to the rubber hose.

If the gauge works, but the sending unit will not cause any movement even when grounded, the sending unit is probably bad. Remove it from the tank and repeat the test with the sending unit wire and ground connected, and the key on. You should be able to move the float arm and change the gauge. There will be a lag time. Replace if it does not respond.

To calibrate, You want the gauge to read the float level accurately. However, most people don't want to run out of gas EXACTLY on E. So most cars are set up to have 2-3 galons left in the tank when it reads E. You also have a pickup that isn't on the bottom, and sloshing that can uncover the pickup. So the best way to check for a sending unit that reads where you want is to have the empty tank out of the car. Install the sending unit in the tank, and connect jumper wires to the circuit and ground the tank. Turn the key on, and it should read below empty with the tank in it's normal position. Turn it upside down, and it should read full or over full.
If it doesn't, you can take the sending unit out and try bending the arm.
To speed this process and avoid constantly removing and installing, here's a tip; If it is not reading right, turn off the ignition and disconnect the wires. Using an Ohmmmeter, measure the resistance in the normal and upside down positions. Remove the sending unit from the tank, and reconnect the ohmmeter. Move the float arm until it reads the same as before. Lay the sending unit on your work bench and mark the location of the float in each position, so you know the range of the swing inside the tank.

Re: Calibrating My Fuel Gauge [Re: RodStRace] #447497
08/23/09 09:33 PM
08/23/09 09:33 PM
Joined: Sep 2005
Posts: 12,481
Chino Valley
RodStRace Offline
I Live Here
RodStRace  Offline
I Live Here

Joined: Sep 2005
Posts: 12,481
Chino Valley
Oh, and Welcome!







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