I bought a 1980 CJ 7 and the fuel gauge doesn't work. Long story short the tank was bad and I figured so was the sending unit. I now have brand a brand new tank & sending unit and hoses clamps etc. Everything is disassembled and off of the vehicle. I noticed during the tear out portion that there were two wire coming off the old sending unit I assumed one was a ground because it was grounded to the frame, the other lead must be low voltage or positive lead that goes all the way to the dash gauge??? I didn't find anything that it would have been connected to? I know the dash gauge must have some lead going to it from the sending unit?? I am better off jut running a brand new single lead all the way up front? Is there a lead that goes all they way up front and I am not seeing it?
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it is probably the sending unit. to fix this you will need to have the sending unit replaced.
You can purchase the sending unit from an auto parts store such as advance or oreilly's. you will need to drop your tank to do the replacement. I did my wife's minivan and it wasn't too bad.
We put the rear wheels up on ramps and blocked the tires as well as set the brake. We used a floor jack with some plywood and blocks to brace the tank. We disconnected the battery, removed the tank bands, lowered the tank, disconnected the wiring and fuel lines as needed, slid the tank out from under the car, removed the fuel pump/sending assy, installed the new assy and reassembled everything. Took about an hour. and it cost about 110 + tax for parts. you may find detailed instructions at autozone.com for your vehicle that will explain this completely. If you aren't up for doing the work yourself, buy the part and take it to a trusted mechanic. i would recommend replacing the pump and sending unit as the trouble of removing the tank is enough that it would be worth your while to do it while you have things apart. This should fix your problem unless it is actually a wiring issue or a guage issue. you will have to do some investigating to see if wiggling wires and checking fuse connections makes any difference. short circuits and bad connections can cause symptoms you are describing but if you find no evidence of if go ahead with the sending unit/fuel pump replacement. Hope this helps.
Most of the time it is the sending unit in the fuel tank.Remove the connection from the fuel tank,and using a test light,test the wires that you removed from the fuel tank. Clip the alligator clip on the test light to a good known ground,and use the probe on the test light to touch the terminals in the connector you unplugged.Make sure the ignition key is turned to the on position,right before start position.Have someone to watch the gauge.At this point the gauge should be showing past the full position.When touching the right terminal in the connector you removed from the tank,the fuel gauge should move down toward the empty mark.If this fuel gauge doe do this when you are testing it,then the gauge in the dash is good and the sending unit is bad.
there is always a small percentage that you have a electrical short, but 90% of the time it will be a FUEL SENDING UNIT, not to be confused with the fuel pump. Check your electrical, Especially the ground wire near; on top of the fuel sending unit which is conviently located on the TOP of your fuel tank, Sorry for the bad news, but you're going to have to drop the tank. Since yo're down there, best to replace the fuel pump since it's all right there in front of you.
Talking about fuel gauge issues and how do you how do you diagnose, ... is the dash unit right here, and obviously the gauge doesn't read correctly. ... to fix the fuel gauge, so you can actually fix the fuel gauge electronically by reflashing the program. ... How to Troubleshoot a Malibu Fuel Gauge & Dash Light Not Working...Could be a bad fuse - fuse # 17 is a 15 amp fuse for the fuel gaugeCould be a bad float on the fuel gauge sending unit inside the gas tank (
it's with your electric fuel pump ) If the float gets a pinhole or
crack in it , the float fills with gas and sinks so the gas guage reads
empty all the time Could be a wiring problem
You definitely have two different issues as the fuel gauge and radio are on different circuits. The radio could be a blown fuse, which would require finding a short circuit. The fuel gauge could be as simple as a bad connection at the sending unit or a lost ground on the fuel tank. Disconnect the fuel gauge at the tank and with a twelve volt test light well grounded probe the harness terminals with the key on (engine off). The fuel gauge should move when the sending unit wire is probed, and the test light should light dimly. Other terminals are a ground for the sending unit, a ground for the fuel pump, and power for the fuel pump. If the gauge moves when the sending unit wire is probed the problem is either the sending unit or a bad harness connection. If the gauge doesn't move during the probe there is a wiring problem (open circuit) or a bad dash gauge. Hope this helps.
you should be able to find the fuel tank harness under the car near the fuel tank. If you look just in front of the rear axle on the drivers side you will see two connectors Unplug the connector with the grey, purple, black, and black/white wires.
Ground the purple wire. Turn the key to the run position. The gauge should read full. If it does you have a bad sending unit (the part in the tank that tells the gauge what the fuel level is at).
If the gauge still reads empty you have a bad gauge.
The computer does a sweep test everytime it senses power. Check it next time you turn the key to run the gages do a little self test. However the fuse and gage won't be your problem. They are very bad for the fuel level sensor in the tank getting corrupted or dirty and doesn't read properly. You can try to add port fuel injector cleaner to the tank, but problem will usually reoccur. You will need the fuel tank dropped and the level sensor replaced.
Most of the time its is the sending unit in the fuel tank. The test for it is to use a variable resistor that is hooked up to the wiring at the fuel tank and watch the fuel gauge if the gauge works ok thats makes 100% sure its the sending unit. At 245 ohms the gauge should read full, 180 ohms for 3/4 full, 160 ohms for 1/2 tank, 100 ohms for 1/4 tank and 42 ohms for empty. The color of wires at the fuel tank is purple wire and black wire. You can also use fixed value resisters. If the fuel gauge the wires from the sending unit to computer then to gauge for bad connections, shorts, broken wire and bad grounds. If the wires test ok that only leaves insterrment cluster or computer which even most dealers can't test eather one but the insterment cluster would be a more common problem then the computer. But about 95% of the time it will be the fuel level sensor in the gas tank that causes the problem. Good luck.
The fuel gauge sending unit which sends a signal to the gauge is stuck or defective. It’s in the fuel tank.
Buy 2 containers of Chevron Techron at Wal-Mart and add to the fuel tank. Sulfur deposits build up on the sending unit. I own a Corvette and many of us owners have had to add the Techron to cure the fuel gauge problem.
If that doesn’t take care of it, more than likely the fuel level sending unit has gone bad, it is inside the tank and is a variable resistor connected to a float. Chevy and GMC trucks in the 99-2003 era have had a bad problem with this. The sending unit can be replaced apart from the pump but this is not a job for a beginner.
It’s best to replace pump and sending unit at the same time. If you only replace sending unit, pump will usually fail soon after that creating extra expense