Possible sender fault

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TOY440

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ok guys, was jacking car up from the diff, slipped off the jack and came down on the jack on the fuel tank. Didn't really damage the tank at all, just a bit of a dint as the jack is a decent size.

I noticed my fuel tank now reads full. I disconnect the feed wire from the sender (I only have one wire, some have 2 wires, like an earth, mine has one), and it still reads full, I earth out the wire, it reads empty but very very slowly creeps towards full.

Any ideas what my issue could be?

Thanks in advance.
 
I think that the tank has a ground wire, or strap, the grounds the tank. Most time it is connected on the fuel tube on the sending unit, to go around the rubber piece.
 
I think that the tank has a ground wire, or strap, the grounds the tank. Most time it is connected on the fuel tube on the sending unit, to go around the rubber piece.


Yeah, some do, some don't, mine doesn't. I'm not too concerned about the earth, I'm concerned why my gauge is reading full all the time now, perhaps I damaged something inside, resistor perhaps......
 
I noticed my fuel tank now reads full. I disconnect the feed wire from the sender (I only have one wire, some have 2 wires, like an earth, mine has one), and it still reads full, I earth out the wire, it reads empty but very very slowly creeps towards full.

If I'm not mistaken the gauge reads full when the resistance to the gauge is low like 10 ohms and empty when the resistance is in the 72 ohm or above range. If you short the sender wire to ground the gauge should read full. If it is not connected or shorted it should read empty. If it is reading full when disconnected and not grounded I suspect you pinched the wire and it is grounded. Grounding the wire and you get empty but slowly raises to full might be you moved the wire away from the sort and when you let the wire be it moves back to the short.

Also it is important to be sure the tank is properly grounded or there is no path for the ground side of the sender to get back to the chassis and make a complete circuit.
 
.....I disconnect the feed wire from the sender......and it still reads full, I earth out the wire, it reads empty but very very slowly creeps towards full.

Sorry this does not make sense. Dana67 ^^ above is correct. When the sender is "full" the resistance is low, causing more current to flow in the gauge. Here are the factory tester values

c-3826-jpg.jpg


I would re-test.......perhaps you did not get the sender wire well connected to ground.
 
I remembered 72 when the value is 74. Not too bad from memory from an old fart like me... now where did I put my glasses!
 
I remembered 72 when the value is 74. Not too bad from memory from an old fart like me... now where did I put my glasses!

That value varies depending "where you read." Bear in mind that value did not come from any Chrysler literature that I'm aware of. It came from guys measuring the dealer tester!!! And they likely vary as well!!
 
That value varies depending "where you read." Bear in mind that value did not come from any Chrysler literature that I'm aware of. It came from guys measuring the dealer tester!!! And they likely vary as well!!

I agree with you Dart. I have seen references ranging from 73ohms to 75 ohms in different readings. I don't think it makes a huge difference in those two numbers.

To test my gauges, I set my power supply to 5volts and verified. My meter read 4.99 volts. I connected two 150 ohm resisters in parallel to make my hi resistance wire. When I test resistance in the test wire after assembling them, I get 74.8 ohms. When I test my gauges with that resister, I barely see the gauge move. I then put in the 23 (22.9 actual) ohm resister wire and the gauge goes to about midpoint. The 10ohm (9.8ohm actual) brings it to just over the max mark.
 
The original post said that the car slipped off the jack and the jack hit the tank. Couldn't the wire going to the sending unit have gotten pinched between the tank and a frame rail? That would ground out that wire and cause the gauge to read full all the time when the key is on.
 
Ok guys, got it sorted. Due to an aftermarket electric fuel pump being fitted, the lines were changed also. There seemed to be an alloy vent tube that may/may not have been used as some type of earth. I have made an earth wire and everything seems to be working fine now.

Thanks for all the advice
 
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