fuel gauge problems

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Onus Gumboot

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Maybe someone can help me here. My fuel gauge quit working. I tested the everything as best I could. I read where you can put a resistor in place of the sending unit at the tank, and a 25 ohm resistor should read about a half tank. And it does. The sending unit read 18 ohms, which is what I would expect with close to 3/4 of a tank. I drove around a while, and it read 23 ohms, meaning less gas than before, so it seems to be working. But when I hook the sending unit back up, nothing. If a resistor, which is all the sending unit is really, makes the gauge work, why would the sending unit not do the same thing?
 
Is the ground from sender to fuel line in place.

Easy test is to get some alligator clips on a wire with fuel in the tank, key in the on position clip one clip to the tube on the sender and one to the frame.

If the gauge reads you have your answer.


Some helpful info regarding resistances and fuel level
Sender resistance in FSM
 
^^That there (ground) and also might be a poor connection in the sender wiper---enough to operate a ohmeter, but fails under "load." That is, looses connection when the current required to operate the gauge is applied.
 
Dana67Dart said:
Is the ground from sender to fuel line in place.

Easy test is to get some alligator clips on a wire with fuel in the tank, key in the on position clip one clip to the tube on the sender and one to the frame.

If the gauge reads you have your answer.


Some helpful info regarding resistances and fuel level
Sender resistance in FSM
Click to expand...
Ground is good. At least it tests good with an ohm meter. Plus I did hook up another wire to ground just in case and still nothing. I looked at the info you posted, and it may be useful, although I hope to figure this out without removing the sender unit. It is brand new which these days doesn't mean much.
 
67Dart273 said:
^^That there (ground) and also might be a poor connection in the sender wiper---enough to operate a ohmeter, but fails under "load." That is, looses connection when the current required to operate the gauge is applied.
Click to expand...
The sending unit is new. But that doesn't mean it isn't bad. This seems like the most likely answer, but I hope not. I don't want to end up buying a lot of the same parts over and over finding a good one. I also ordered a new instrument voltage limiter just in case that is causing the problem, but the temp gauge works, so I don't know.
 
Try this......

"Rig" the sender connection however you must for electrical access. Alligator clip, etc. With the key "one" and the thing hooked up to operate "as normal" put your meter on low volts. Stab one probe hard into the sender ground IE any metal on the sender, and stab the other probe hard into a body ground point. You should read ZERO voltage. If not, it is not grounded

I believe you said you already tested the gauge for operation with a resistor. Did you connect your test resistor right at the tank connection? This will test all of the sender wire. If not, retest, and see if it still works. If so, and if the ground test above is good, it HAS to be a sender problem

You could double check by doing the following: Hook your meter up for current measurement, one probe hooked to sender, other probe connected to sender wire. If the fuel gauge does not read, check the multimeter, likely zero current. You can double check that by again connecting your test resistor, as sender wire---meter probe--through meter--meter probe--test resistor--ground, and you will see the meter reading.
 
67Dart273 said:
Try this......

"Rig" the sender connection however you must for electrical access. Alligator clip, etc. With the key "one" and the thing hooked up to operate "as normal" put your meter on low volts. Stab one probe hard into the sender ground IE any metal on the sender, and stab the other probe hard into a body ground point. You should read ZERO voltage. If not, it is not grounded

I believe you said you already tested the gauge for operation with a resistor. Did you connect your test resistor right at the tank connection? This will test all of the sender wire. If not, retest, and see if it still works. If so, and if the ground test above is good, it HAS to be a sender problem

You could double check by doing the following: Hook your meter up for current measurement, one probe hooked to sender, other probe connected to sender wire. If the fuel gauge does not read, check the multimeter, likely zero current. You can double check that by again connecting your test resistor, as sender wire---meter probe--through meter--meter probe--test resistor--ground, and you will see the meter reading.
Click to expand...
Thanks for the ideas. I did the ground test and it comes out good. I did the resistor test at the tank, so it should be good from there. It is a brand new tank and sender unit. All new stuff back there. There has been a lot of talk though, on various car channels about an epidemic of bad parts, so new may not mean anything. I'll try the current test as you stated as soon as I get the chance. I have to get back to the real world for a while, so it may be next week before I get a chance to try it. Thanks again for the input.
 
My bet would be a bad wiper arm contact on the sender. You might even be able to fix it. You may be aware, repop senders are very inaccurate. There was a thread on here about improving them, and there is a device you can buy called a "metermatch" that is programmable and several different points to correct the reading. I have not used one as such, but I did buy one, set it up and do some testing.
 
There is the answer, he installed a new aftermarket sender. Not a reconditioned original sending unit. If I have read and understand correctly.
 
The connector that slips on the stud of the sender might not be making connection.

Try an alagator clip from sender wire connector to sender wire post.

If it works you have an answer.

Also some senders have a nut on the sender post it might be preventing the sender wire connector from going on far enough.

The test above will point to that as well
 
67Dart273 said:
My bet would be a bad wiper arm contact on the sender. You might even be able to fix it. You may be aware, repop senders are very inaccurate. There was a thread on here about improving them, and there is a device you can buy called a "metermatch" that is programmable and several different points to correct the reading. I have not used one as such, but I did buy one, set it up and do some testing.
Click to expand...
I'll look into these suggestions as soon as I get the chance. I don't know if I mentioned though, The gauge was working fine for a two or three months before going dead. I don't know if that means anything or not. But it seems like it would rule out bad connections where the wire attaches to the sending unit. Although not necessarily. You would think all the taking it off and on would get it back if that was the case. I don't think I even drove from the last time I saw it working to the time I noticed it wasn't, so if something came loose inside, I don't know how. I need to drive it long enough that there isn't going to be a high enough level of fuel to spill out when I take the unit out, if it comes to that. It probably will eventually.
 
Onus Gumboot said:
I'll look into these suggestions as soon as I get the chance. I don't know if I mentioned though, The gauge was working fine for a two or three months before going dead. I don't know if that means anything or not. But it seems like it would rule out bad connections where the wire attaches to the sending unit. Although not necessarily. You would think all the taking it off and on would get it back if that was the case. I don't think I even drove from the last time I saw it working to the time I noticed it wasn't, so if something came loose inside, I don't know how. I need to drive it long enough that there isn't going to be a high enough level of fuel to spill out when I take the unit out, if it comes to that. It probably will eventually.
Click to expand...
 
You might want to pull the instrument cluster and check the circuit board. I recently had to replace the left one that controls the fuel guage because it was burnt. My guage works now , but is showing about a 1/4 tank lower than what is in it! Still trying to figure out what is causing this.
 
Airstream65 said:
You might want to pull the instrument cluster and check the circuit board. I recently had to replace the left one that controls the fuel guage because it was burnt. My guage works now , but is showing about a 1/4 tank lower than what is in it! Still trying to figure out what is causing this.
Click to expand...
I cleaned up the circuit board months ago. soldered some loose pins on the connector. everything was working until the fuel gauge stopped. I am going to replace the voltage limiter. That could be the problem you're having. I've heard those were pretty unreliable even when they were new. The one I have coming is supposed to be an upgrade from the old ones. They said it was one of the reasons the fuel gauge was never accurate back in the day. At least that was the selling point. I guess I'll find out when it gets here. I may pull the cluster again, and see if all the pins are still ight on that connector. I don't think that's the problem, because the gauge works when I put a resistor on the sending unit wire. Time will tell.
 
The limiter will affect the temp gauge as well. That is the key, "if they both" act up............

Some general ramblings, some of which you may already have done.

I try to encourage you guys to think of "the system" "end to end" "the path."

In this case "the path" is from the key---power up to the harness connector, harness pin to board traces, to the limiter spring contact on the board--through the limiter---back out another spring terminal and board trace---and feed to the temp and fuel gauge studs. Through the fuel gauge, out the sender stud, to the board trace, back to a harness connector pin, to the sender wire, down to the left kick panel connector, back on the tail harness, through the trunk, and down to the sender, through the sender, grounded through the fuel line clip, and "maybe" to body ground

You need to be suspicious of, and check all of these points, 'specially now that these girls are some 50 years old

Inspect the harness connector pins. If they appear loose or corroded, clean them up good use some ELECTRICALLY COMPATIBLE flux (not plumbing, etc, which is acid) and use electrically compatible solder to solder the pins to the traces.

Solder jumpers across the IVR contacts to the board traces. These, if you look, are just crimped into the board, and can loose contact.

The gauge studs can lose contact. Clean the copper around the board terminal, and loosen/ tighten the nut a few times to "scrub" the connection.

Rig the thing up with 12.6--14V power to the appropriate harness pin, and use resistors to check gauge accuracy. All three gauges (oil in a Ralley) essentially follow the same resistance

Suspect things like the push-on wire terminals at the temp and fuel sender. suspect grounding at the fuel sender.

Take nothing for granted. For example, one problem child turned out simply to be a bad power feed to the cluster. Enough to make the warning lamps glow, but intermittent and would not reliably operate the gauges accurately.

On my old 67 the harness pins some were broken, I simply soldered pigtail wires to the board traces and used a pair of "Molex" style connectors and got rid of the factory ones

CLUSTER GROUND. Clusters are "accidently" and poorly grounded by the mounting screws. Find a good common ground point on the cluster, install a pigtail wire, and bolt it to the cash frame/ column support.
 
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