Fuel gauge not working
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Old August 29th, 2011, 04:51 AM   1 links from elsewhere to this Post. Click to view. #1
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Fuel gauge not working


My 91 gt has a fuel gauge that isn't working. Where is the fuel sensor located? I know the fuel pump is in the tank, but from a picture I looked at I only see two wires going to the fuel pump assembly which looks like a positive and ground for the pump itself.

I don't see a flotation arm assembly so how do these cars measure or track the amount of fuel in the tank?

I am not sure if its a sender or the gauge itself.

Is there any way I can test the gauge with a multimeter or run a lead to it to determine if its working?
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Old August 29th, 2011, 11:36 AM   #2
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Sender is attached to the pick-up. It has a float on it.

If you want to test the gauge you can send ground to the yel/wht wire coming from the sending unit and see if the gauge moves.
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Old August 29th, 2011, 02:25 PM   #3
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Originally Posted by fogged306 View Post
Sender is attached to the pick-up. It has a float on it.

If you want to test the gauge you can send ground to the yel/wht wire coming from the sending unit and see if the gauge moves.
So I take the yellow/white wire and ground it out to see if it moves?

I can have someone sit in the car and watch the gauge while I ground it out.
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Old August 29th, 2011, 03:32 PM   #4
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Yep. All the sender does is send a ground signal through it. The float is just on a variable resistor with ground on one end and the gauge on the other. I'm not sure which way is more resistance, but either way, if you send the gauge solid ground and it pegs full or empty, the gauge is ok and so is the wiring coming from the sender.
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Old August 29th, 2011, 04:11 PM   #5
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A little FYI, something that happen to my car was the baffle come lose in the tank, therefore cutting the wire that runs to the float. Safe bet would be drain the fuel and drop the tank and look inside. Just my 2 cents worth and my problems i had before.
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Old August 30th, 2011, 09:44 AM   #6
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I don't know if it matters but the guage always reads 1/2. It is always at the same point, never any lower or higher and it never moves whether the car is running or not. It doesn't cycle when the ignition is turned on or anything. It's like the gauge is glued in one spot. I will try the ground idea and see if that gets it to move.
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Old August 30th, 2011, 10:03 AM   #7
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Just had a issue like this my gauge was pinned to full i took it to a shop it was just a wire loose on the back of the gauge fixd it then my tank started reading........ Somewhat when i filled it up wen i left the shop the tank ready half full. You can imagine my suprise. Then took it back they calld later and said it was the sending unit and it was gna cost 300 to fix it i told them to giv my car back cuz i wasnt paying 300 for a part i can buy and install for 80 bucks at autozone.
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Old August 30th, 2011, 10:06 AM   #8
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Also they chargd me 140 for like 5 seconds of work correcting the wire on the gauge. I guess they are used to dealing with people that dont know wuts goin on with prices on parts for their own vehicle but seriously
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Old August 30th, 2011, 10:19 AM   #9
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Well I just encountered another problem. Now my voltage gauge has quit working as well.

I started the car a little bit ago and instantly turned the lights on and the voltage gauge dropped to zero and is not working.

I checked the voltage at the battery with a multimeter and it shows the alternator is still putting out power. Also when I disconnected the battery while the car was running the car kept running off the alternator so it wasn't the 3G I just put in.

The voltage gauge was working and just suddenly quit today.

Not working:

Fuel gauge
Temp gauge
oil pressure
voltage

Working:

Tachometer
Speedometer

The speedo is mechanical I know so it would keep working.

How does the tachometer work? Is it electrical or mechanical? So far the tachometer is still working.

Do you think the cluster voltage regulator has failed?

I have since bypassed the water temp and oil pressure gauges. It looks like I might have to do the same thing with the rest.
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Old August 30th, 2011, 12:16 PM   #10
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I found an aftermarket fuel level gauge that can be used for ohm levels 10-180 and 16-158.

The 91 mustang has an ohm level of 22@empty and 148@full so these ohm levels fall within the gauges ability to read the fuel level.

My question is, does this mean the gauge won't actually know my tank is empty at 22 ohms and will never read completely empty? Does it have to receive 16 ohms for the E mark?

I wasn't sure if I was understanding it correctly.

The gauge works with multiple sending units and ohm levels and since there all different, how would the gauge even know which is which and what the tank level was really at?
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Old August 30th, 2011, 01:05 PM   #11
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lol get this. Since none of my gauges were working, I decided to peg the old oil pressure wire just to see if the gauge would move.

I put a wire in that single oil pressure wire and touched it to the ground, nothing happened. Then I touched it to the positive terminal and the oil pressure gauge pegged to zero. So that gauge is working.

That's not all. Now my voltage gauge is working again and showing proper voltage. Also, my TEMP gauge is responding again.

Sadly though the fuel gauge is still NOT working. It is still showing 1/2 a tank of fuel.

I am going to pull the cluster tomorrow and check the resistance of the fuel sending unit from behind the dash. I read there is only one wire behind the cluster that will give an ohm reading so I don't actually have to drop the tank to check it there untill I get zero ohms this way.
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Old August 30th, 2011, 01:26 PM   #12
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there is a connector back at the tank too. you can ring the wires from that to the dash to verify the wiring and gage before spending the time to drop the tank.
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Old August 30th, 2011, 05:51 PM   #13
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Originally Posted by Stdyhand View Post
lol get this. Since none of my gauges were working, I decided to peg the old oil pressure wire just to see if the gauge would move.

I put a wire in that single oil pressure wire and touched it to the ground, nothing happened. Then I touched it to the positive terminal and the oil pressure gauge pegged to zero. So that gauge is working.

That's not all. Now my voltage gauge is working again and showing proper voltage. Also, my TEMP gauge is responding again.

Sadly though the fuel gauge is still NOT working. It is still showing 1/2 a tank of fuel.

I am going to pull the cluster tomorrow and check the resistance of the fuel sending unit from behind the dash. I read there is only one wire behind the cluster that will give an ohm reading so I don't actually have to drop the tank to check it there untill I get zero ohms this way.

Sounds like someone has had the dash out of your car before! Most likely to change the heater core. The plugs are old and break the keeper tabs real easy. You may be in for a long job or search, the dash is a bitch to pull. Have a buddy help you and pay attention to hook up all plugs,hoses and cables, etc.
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Old August 30th, 2011, 10:42 PM   #14
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Originally Posted by BULLET20XD View Post
Sounds like someone has had the dash out of your car before! Most likely to change the heater core. The plugs are old and break the keeper tabs real easy. You may be in for a long job or search, the dash is a bitch to pull. Have a buddy help you and pay attention to hook up all plugs,hoses and cables, etc.
When I bought the car the last owner said he had pulled the cluster before but didn't mention the dash. But I think your probably right. I don't think he installed the cluster correctly and both floor pans need to be replaced due to being rusted through. I originally thought it was due to leaking door seals because they were leaking badly, but it could be due to a heater core and they got it replaced. If they did pull the dash they done a decent job putting it back because I can't tell it was ever pulled.
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Old August 31st, 2011, 07:12 AM   #15
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Originally Posted by Stdyhand View Post
When I bought the car the last owner said he had pulled the cluster before but didn't mention the dash. But I think your probably right. I don't think he installed the cluster correctly and both floor pans need to be replaced due to being rusted through. I originally thought it was due to leaking door seals because they were leaking badly, but it could be due to a heater core and they got it replaced. If they did pull the dash they done a decent job putting it back because I can't tell it was ever pulled.
I pulled my dash back in the winter and unless you see some of my plug keeper tabs broken, you would never know its been pulled. If you do pull the dash, i feel for you. I would do what you said first and pull the cluster and avoid the dash if possible? Good luck!!!
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