- Jul 21, 2015
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Fuel Gauge
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horse sence
15 Year Member
- Jul 21, 2015
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Hey Jim...My name is Nick and I am pretty well schooled on mechanics...so they all say....anyway I have 3 wiring diagrams....I have been trying to figure this out for weeks.....Im not wanting someone to fix it...I challenge someone to figure this out! I have two sending units and they both work outside the tank but when installed in the tank they do no function....I have ran a ground from the battery straight to the tank to make sure it was getting ground....I have a new instrument cluster solid state regulator...I have two fuel gauges...both work.....I have 5 volts all the way to the terminal that connects to the sending unit at the tank.....I challenge anyone to figure out this problem because I am STUMPED!.....I would REALLY appreciate any thoughts on this
- Jul 21, 2015
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horse sence
15 Year Member
I believe you have a ground problem ,it is fairly common on mustangs .The tank is only grounded through the the screws that hold the tank in place .There is sealer between the tank and the body so sometimes the ground can be lost . Try grounding your sender directly to the body ,if it reads when the sender if moved up and down then it is a ground problem with the tank. A ground strap may help .
- Jul 21, 2015
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I Wish it was that simple....I have ran a ground wire straight from the battery to the tank....I have ran a ground wire from a tank screw to the sending unit.....tonight i actually drained the tank for the 5th time and physically took the sending unit and lowered it in to a bucket with fuel in it and it worked.....I stuck it back in the tank and it did not work again....I did take another volt reading and on the back of the fuel gauge I have a solid 5 volts on one side and 3.50 or so coming out the other side...I have about 8 gallons of fuel in the tank and the gauge reads 1 quarter tank?.....I have two fuel gauges and they both read the same?...THOUGHTS?
horse sence
15 Year Member
Empty the tank and replace the sender and see if it shows empty .
It still sounds like a ground to me , do you have a ground from the motor to the body ? You may only be grounding from the battery to the motor .
It still sounds like a ground to me , do you have a ground from the motor to the body ? You may only be grounding from the battery to the motor .
horse sence
15 Year Member
One more test you might try ,pull the wire off the sender and ground it directly to the tank and nothing else . The fuel gauge should go to full if you have a good ground .
- Jul 21, 2015
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I have done that test and the gauge plummits towards full....Ive had my wife watch the gauge while I grounded the wire that hooks up to the sending unit...this is why I say Im stumped?
horse sence
15 Year Member
If the gauge goes to full when grounded then it has to be after the wire /sender or ground .May be a bad sender ,did it ever read correctly ?
- Jul 21, 2015
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the old one didn't so I bought a new one,,,,when I removed the bad sender it had a plastic float on it that was full of fuel.....actually the sender was still good but I put the new one in anyway.....if I take the wire off the sender the fuel gauge heads towards the full mark fast.....I guess I will drain the tank for the 7th time and retest the ohms reading on the sender....watch the fuel gauge operate proper and keep repeating...I WILL NOT GIVE UP!....any advice would greatly be appreciated
- Jul 21, 2015
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ok....heres where im at....drained the tank......took one of the tank mounting screws out....drilled it out a little....took a die grinder and sanded the top of the hole....stuck a 1/4 inch bolt through it but before I did that I took my did grinder and sanded the frame underneath for a good connection....I stuck the bolt through with a washer on top of the tank to get plenty of ground and on the bottom I did the same.....I KNOW that tank is grounded......now when I take a 5 gallon bucket and hold the sending unit in the bucket full of fuel the fuel gauge works....now with that said I checked voltage where I jumped off the yellow and black wire that runs along the door jam....I stripped it so I could sit on the carpet and perform my test......the voltage directly on the wire is 5 volts...exactly what it should be coming to the sending unit....but when I hook the wire to the sending unit terminal and check voltage it shows 1 to 2 volts then at times nothing...I can even touch the jumper wire that is connected to the sending unit terminal and it reads nothing....but the fuel gauge is working?....I guess at this point even though I have two sending units I will buy another and try it........I am sure you are good at electrical and I am no dummy but if you have any thoughts on this I still would greatly appreciate it
horse sence
15 Year Member
- Jul 21, 2015
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I was hopeing you were up for the challenge......I put the sending unit in a bucket of fuel....hooked the hot lead up...hooked a ground lead up and it worked again....so this time I thought I would trick it to think I was hooking it up to the tank so I hooked a third test lead up from the sending unit base to the fuel tank where it mounts...the stupid thing still read correct..i was hopeing it was grounding out or something stupid....hope you are still up for the challenge...if not I guess im on my own,,,if you give up how can I get someone else to help....if you come up wth something please feel free to impress meGot me stumped
horse sence
15 Year Member
What i was thinking is, it wasn't adjusted properly .That is why i was wondering what it read on a empty tank ,if it doesn't read empty maybe it is set wrong . Without having my hands on it, it is hard to say .
- Jul 21, 2015
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when I put it in my hands it reads empty when the float is against the pick up tube screen and full when it is raised to its highest level....ive even done the ohms reading....8 on lowest and 68 on highest I think.....its annoying...im gonna put it back in the bucket with fuel.......and try once again to make it think it is in the tank.....I will hook a test lead to it and ground it to the tank and I will ground it to the frame of the car.....now that im thinking about it I did unhook my speedo cable and I couldn't get it to mess up...I know that shouldn't matter but ive seen stranger things....im gonna hook my speedo cable back up and like it was before and put it in the bucket and ground the unit to the tank....that thing doesn't have a brain.....it doesn't know where its at....but then again!....
- Jul 21, 2015
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ok...new update......when I put it in the bucket of fuel it reads full on my fuel gauge and seems to work proper....but...when I took it out I did another ohms reading just to check and it reads like 0 ohms on empty and maybe 20 ohms on full....I really don't know why my fuel gauge seems to work but the ohms reading isn't correct....also it doesn't stay at 20...after a few seconds it goes nuts...20 to 60 to 100...then kinda starts over.....also I have a solid 5 volts on the test lead but when I hook it to the terminal and check it only has a little over 2volts....then I check the voltage down at the black wire that connects to the resister or what ever it is on the sender and I only have 1.85 volts....I even checked the ohms on the other sender and it doesn't read right....also...should there be continuity if I touch the hot terminal with the red lead and touch the sender with the ground lead?...that was throwing me.....I know this is a lot but I know you understand......would you be so kind to give me detailed answers to all this......thanks Jim...Nick
horse sence
15 Year Member
Well i believe the ohms would have to change from the empty position to the full position for the gauge to get a reading ,and i would think the lowest reading would be at the empty point and the full would be the highest reading .
Placing it in a bucket of fuel will not give you a full or empty reading though, It will have to get a full or empty reading from being inside the tank ,otherwise it will be no different than moving the float with your hand . Did you get a reading on the gauge with it in the empty tank ?
Placing it in a bucket of fuel will not give you a full or empty reading though, It will have to get a full or empty reading from being inside the tank ,otherwise it will be no different than moving the float with your hand . Did you get a reading on the gauge with it in the empty tank ?
- Jul 21, 2015
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why would it not read right in a bucket full of fuel...im not understanding....I feed the hot terminal 5 volts and ground it and the float moves...when it moves to full the gauge moves...when I make the float go to the screen it reads empty....but......it is not reading ohms proper...it reads empty in the tank when installed and the tank is empty of coarse......I add fuel and it doesn't read proper......I filled the tank up like you said and it read 1/4 tank
horse sence
15 Year Member
because in a bucket of fuel you are really only testing the float because the sender isn't in a fixed position as it is in the tank . Do all the other gauges read properly .
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