Fuel gauge reading full with no gas in tank

[johnnystc]

I installed a new fuel tank float/sender in my 1966 Bird. As soon as I turn the key on the gauge goes to full with no gas in tank. Is this how it is suppose to work? Hate to put gas into tank and find out I have something wrong and have to remove the float/sender. BTW it is the standard sender w/o low fuel warning system and I replace the CVR behind the dash.

[jopizz]

It should not read full when the tank is empty. Remove the wire plug from the sender. If the gauge goes to empty then your problem is with the sender. If it stays at full then you have a wiring or gauge problem. Make sure the CVR is properly grounded.

John

[simplyconnected]

John is right. Gauges usually fail 'open'. Meaning, they simply don't respond. So, it looks to me like your gauge is ok.
Get your meter or test light out and test that wire on your fuel tank sender. You should see pulsing 12-volts to ground. If you see steady voltage with no pulsing, your CVR contacts are welded shut. Any short circuit to ground on that float wire will also cause your gauge to fail as you describe.

So, I would start at the fuel tank, disconnecting the wire. Then, look at your gauge. If no change, then as John said, check your CVR for proper ground to the steel case. An ungrounded case will also make your gauge read, 'full', just like stuck contacts.

Both (fuel & temp) gauges are fed from the same CVR. If one pegs the needle, then both should act the same. Follow these instructions without getting sidetracked and get back with us to report your findings.

BTW, I rebuild original CVRs with solid state components. - Dave

[johnnystc]

Thanks for info. Will try to get to it tomorrow. You guys are great resource

[johnnystc]

Ok removed the plug and fuel gauge is 0. Then tried to measure voltage with my cheap meter and all i get is about 5 volts. Seems constant but maybe a meter issue. Sounds like your note above leads to a bad new tank sensor???

[jopizz]

It definitely sounds like the sensor. I would remove it from the tank, connect the wire plug, turn the key on and test it by moving the float up and down and watch your gauge. Make sure you ground the sensor when you test it. Use a wire with a couple of alligator clips and solidly ground it to the car body or frame. If you get no gauge movement when you raise and lower the float then it's defective. A lot of the new reproduction parts are junk. It's a crap shoot whether you get a good one or not.

John

[johnnystc]

Ok will try it. Thanks

[simplyconnected]

The resistance values of your tank sending unit should range from 100-ohms (when empty) down to 10-ohms (when full). Do your resistance checks out of the tank with NO power.

The same holds true for the TEMP sending unit.

BTW, is your TEMP gauge working? If so, your CVR is ok.

[johnnystc]

Well I finally was able to get time to remove the tank float/sender and check it out with a few wires. Looks like it is bad even though it's new. Just does not read smoothly full to empty. Also ohms don't read correctly. I'll try a new one. Thanks everyone for suggestions and will update when I get a new one.

[johnnystc]

Well I got a new float/sensor and put it in yesterday. Same o same o. Still reading full when installed. Got it from Ecklers which I've had no problem with their products. I'm baffled.

[jopizz]

Once again check it outside of the tank. Don't assume anything. With the float at the very bottom of it's travel your gauge should read empty. Move the float to halfway and then full and check your gauge. If it's working fine outside the tank then your gas tank is probably not grounded well enough. Connect a wire to the tank flange and ground it to the frame of the car. The gas tank straps don't do a very good job of grounding the tank.

John

[simplyconnected]

What resistance readings are you getting with the new fuel sending units?
Ok, you already know that your gauge reads 'full' with the sending unit wire connected to ground.
If you want to prove your system, buy a 50-ohm, 1/4-watt resistor, and let it substitute your fuel sending unit. Your gauge should read '1/2' full. - Dave

[jopizz]

Be aware that your sender has a separate ground wire so it doesn't totally rely on the tank for a ground. I would trace the black wire from the sender plug and make sure it goes to a solid ground point.

John

[johnnystc]

OK more investigation follows. Thanks guys

[johnnystc]

Well I've checked the ground wire and it's fine. I'm thinking I'll pour 5 gallons of gas in and see what happens. I haven't started the car in years but ran fine before restoring. However, now my headlights and front park lights are not working????. I replaced the headlight switch months ago and they were working fine until last week. Tail light, brake lights and signal lights work fine.Inside lights also fine. What do you think.. Switch go bad or the 18 amp circuit breaker (which I don't know where it is).