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Old 01-19-2009, 04:48 PM   #1
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gas gauge stopped working! please help!

I have a 1990 mustang gt. and the gas gauge stopped working completely. when the car is off the neadle goes up to a quarter tank. but when I turn the key on it drops down below empty and stays untill I turn the car off. I really need to get it fixed! so any help would be great!

thanks scott
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Old 01-19-2009, 04:49 PM   #2
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Re: gas gauge stopped working! please help!

It's probably the sender unit in the gas tank.
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Old 01-19-2009, 04:56 PM   #3
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Re: gas gauge stopped working! please help!

Is there anyway i can check to see if it is bad?
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Old 01-20-2009, 07:28 AM   #4
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Re: gas gauge stopped working! please help!

might give ya a idea on how to do it Ford Mustang Fuel Sending Unit Replacement - Mustang Monthly

Somthing I came found

The red/yellow wire (power supply to gauge & sender) should have 12 volts when the ignition is in the start or Run position.

The next steps require dropping the fuel tank and removal of the fuel level sender. Here are some useful tips...

the main issues are getting the car up on jack stands and getting the gas out of the tank. DO NOT try to do this job without jack stands. Becoming a pancake is not part of the repair process.

Pumping out the old gas:
If the old pump still works, you can use it to pump the tank out.
1.) Separate the pressure line (the one with the Schrader valve on it) using the fuel line tools.
Look in the A/C repair section for the fuel line tools. They look like little plastic top hats. You will need the 1/2" & 5/8" ones. The hat shaped section goes on facing the large part of the coupling. Then you press hard on the brim until it forces the sleeve into the coupling and releases the spring. You may need someone to pull on the line while you press on the coupling.


Use a piece of garden hose to run from the pressure line to your bucket or gas can. Make sure it is as leak proof as you can make it. Fire and explosion are not part of the repair process...

2.) Jumper the fuel pump test point to ground.

Turn the ignition switch to the Run position. the fuel pump will pump the tank almost dry unless the battery runs down first.

Some 5 gallon paint pails lined with garbage bags are good to hold the gas. The garbage bags provide a clean liner for the pails and keep the loose trash out of the gas so you can reuse it. If you decide to use a siphon, a piece of 1/2" garden hose stuck down the filler neck will siphon all but a gallon or so of the gas.

Remove the filler neck bolts and put them in a zip bag. Disconnect the supply & return lines by removing the plastic clips from the metal tubing. If you damage the clips, you can get new ones form the auto part store for just a few dollars. I have used tie-wraps, but that is not the best choice. Then you remove the two 9/16" nuts that hold the T bolts to the straps. Put the nuts in the zip bag with the filler bolts. Pull the plastic shield down and away from the tank. Once the tank drops a little bit you can disconnect the wiring for the pump & fuel quantity sender.

The fuel gauge sender assembly comes out by removing a large metal ring that unscrews from the tank. There is a separate mounting/access plate for the fuel pump and fuel gage. You are supposed to use a brass punch to tap on the ring so that you don't make sparks. Look closely at the rubber O ring gasket when you remove the fuel gauge sender.
When you install the metal ring that holds the sender in place, watch out for the gasket O ring. Some RTV may be helpful if the ring is not in excellent condition.

The tank to filler pipe seal is a large rubber grommet. Inspect it for hardening, tears and damage. At $20 from the Ford dealer, it might be a good idea to replace it.

use a floor jack or some friends to help lift the tank back in place.

All resistance measurements should be made with the power off.

Note from bstrd86 - 86 and older fuel tank sender units are 73 ohms empty, 8-12 ohms full.

The yellow/white wire will show a voltage that varies with the movement of the float on the sender unit. To test the sender, set your Ohmmeter or DVM on low Ohms. Then disconnect the sender and connect the Ohmmeter or DVM to the yellow/white and black wires from the sender unit. Move the float arm while watching the Ohmmeter or DVM. You should see the reading change from 22 to 145 ohms +/- 10%.

If the Ohmmeter or DVM resistance readings are way off, replace the tank sender unit.

Use extreme caution if you do the next step. Fumes from the gas tank can easily ignite and cause a fire or explosion.
With the sender unit out of the tank and connected to the body wiring harness, turn the ignition switch to the Run position. Move the float arm and the fuel gauge indicator should move. If you are very careful, you can use a pair of safety pins inserted in the connector for the yellow/white and black wires to measure the voltage as you move the float arm. The voltage will change, but I have no specs for what it should be.
Do not short the safety pins together or to ground. If you do, you may damage the anti-slosh module or crate a spark. A spark with the fuel tank open could cause a fire or an explosion.

If the voltage does not change and the tanks sender passed the resistance tests, the anti-slosh module or gauge is bad.
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Old 01-20-2009, 08:25 AM   #5
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Re: gas gauge stopped working! please help!

could it be the needle is loose on the gauge cluster? have you swapped the gauges our or anything? Just a thought before you drive into the tank.
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Old 01-20-2009, 10:30 AM   #6
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Re: gas gauge stopped working! please help!

deffently the sending unit. If it was a problem with the gauge itself, it wouldn't move much at all. I would upgrade your fuel pump while your in their.
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Old 01-20-2009, 11:46 AM   #7
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Re: gas gauge stopped working! please help!

thanks for all the help. is there anything ells it could be besides the sender unit? cause I don't want to replace the sender unit and then find out the problem was something easy and cheap.

thanks scott
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Old 01-20-2009, 12:15 PM   #8
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Re: gas gauge stopped working! please help!

Question, I've had an issue like this..

Do you have any issue with your voltage gauge/temp gauge? IE when voltage load increases (like turning headlights on) does the voltage gauge drop a good bit, and temp gauge climb?

I ended up having a loose ground at the back of the instrument cluster, all my electrical gauges (voltage/temp/oil pressure/fuel) were acting a bit strange, fuel and temp acted the worst...
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Old 01-20-2009, 12:38 PM   #9
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Re: gas gauge stopped working! please help!

yes my voltage gauge does drop when then the load is increased. And Ive noticed that my oil pressure gauge moves around alot. And my temp gauge and and gas gauge dont work at all. Did all the gauges work fine after u fixed the ground?

thanks scott
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Old 01-20-2009, 05:10 PM   #10
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Re: gas gauge stopped working! please help!

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Originally Posted by ugafan_1207 View Post
yes my voltage gauge does drop when then the load is increased. And Ive noticed that my oil pressure gauge moves around alot. And my temp gauge and and gas gauge dont work at all. Did all the gauges work fine after u fixed the ground?

thanks scott
Yes, gauges worked fine afterward - It may or may not be your problem.. I pulled the instrument cluster out as the previous owner had it apart to run an aftermarket tach through the dash and it's also got an aftermarket alarm system so I wanted to see if anything was loose/pinched/etc -

I didn't see anything obvious, so I started checking the grounds (just the wires off the harness/connector - the one I found heading down toward the clutch/brake/etc looked like it was sliding out.. When I pulled on it, it was loose, tightened it up, didn't see anything else out of the ordinary, buttoned it back up and it was fine since..
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Old 01-22-2009, 08:16 AM   #11
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Re: gas gauge stopped working! please help!

well I took the instrument cluster apart and didnt see anything out of the ordinary. So I went to autozone and bought a 6 dollar temperature switch, and that fixed my temp gauge. So now im pretty sure the fuel sending unit is the reason my gas gauge isnt' working. Thanks for all the help,

scott
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Old 02-04-2009, 11:15 AM   #12
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Re: gas gauge stopped working! please help!

well I replaced the fuel sending unit and it still does the same thing. When the car is off the needle goes up to a quarter tank. But when I turn the Key on it drops below E. Could it be the gauge or is it the wiring?

thanks scott
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Old 02-05-2009, 06:47 PM   #13
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Re: gas gauge stopped working! please help!

I had the same problem with my truck.. the gauge was all jacked up... changed the entire fuelpump and still didnt fix the problem.... got rid of the truck cause of a F.ed up fuelsystem problem.... so i dont know what caused it.
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Old 02-05-2009, 07:08 PM   #14
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Re: gas gauge stopped working! please help!

Im thinking its either wiring or the gauge its self. Ive replaced the fuel sending unit. So is there anything ells it could be?
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Old 02-05-2009, 11:53 PM   #15
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Re: gas gauge stopped working! please help!

Quote:
Im thinking its either wiring or the gauge its self. Ive replaced the fuel sending unit. So is there anything ells it could be?
could be a loose ground wire. Usually a loose ground causes weird things to happen
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Old 02-06-2009, 07:05 AM   #16
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Re: gas gauge stopped working! please help!

what about that slosh module the other guy talked about earlier? did you change that?
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Old 02-08-2009, 03:37 PM   #17
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Re: gas gauge stopped working! please help!

I took the slosh module out and I turned the key on and the needle went up past F. does that mean its good or bad?
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Old 02-11-2009, 01:27 PM   #18
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Re: gas gauge stopped working! please help!

I fixed it the slosh module was bad. thanks for all the help.

scott
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Old 01-14-2011, 01:18 AM   #19
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Re: gas gauge stopped working! please help!

Quote:
Originally Posted by MonteCitan View Post
Question, I've had an issue like this..

Do you have any issue with your voltage gauge/temp gauge? IE when voltage load increases (like turning headlights on) does the voltage gauge drop a good bit, and temp gauge climb?

I ended up having a loose ground at the back of the instrument cluster, all my electrical gauges (voltage/temp/oil pressure/fuel) were acting a bit strange, fuel and temp acted the worst...
Oh i HAVE that issue with my 94! I have subs and whenever they hit that electrical load makes my temp gauge go up! my battery and oil gauge are effected, but i havent really noticed by gas gauge move at all! so i gotta take the I.C. out and check for a loose ground!? How long and hard would it be to take out the i.c?
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