Fuel send unit and gauge issue

[Sparxx]

Hope this is the right spot to post this. Replaced the fuel sending unit in my 71 Challenger. Gauge still isn't working. Tested the gauge with the batteries and it's good. Tested the wire to the gauge by grounding it and the gauge reads full so that's good. Tested the ohms on the sending unit. It reads 32 which it has just over a half tank so that's good. Regrounded it numerous ways and still nothing. Ran a ground jumper from bare frame to unit nothing. Got pissed ran a ground from the battery right to the unit still nothing. I'm at a loss here. What am I missing?

[dodj]

When you tested the gauge with batteries, was it battery juice straight to the gauge, or was the voltage limiter included in the cct?

[Sparxx]

Straight to the gauge

[dodj]

You will need to verify that your limiter is working. It may not be putting out the 5v needed to power the cct. Does your temp gauge work?

[chargerdon]

you said tested the wire by grounding at the unit and the gauge read full.   If that is the case then your voltage limiter must be working, and the gauge works and wire from sending unit to gauge all good.   

You also said that you tested the sending unit ohms at it was 32 ohms...was that out of the car or right at the sending unit output?   One thing to check, if i remember right, there is a ground strap that goes from the fuel line to the sending unit.   Make sure that is in place or that the sending unit has ground !!! 

[Sparxx]

@dodj new to this what is the limiter and where is it? All my other gauges seem to be working fine.
@chargerdon  that was with the unit in the tank. Ground strap is on and I've even tried another ground to the frame and also one straight to the battery. Still didn't work.

[7212Mopar]

Take the DS kick panel by the parking brake off. You will see the a wire connector, blue wire. See if it is lose or corroded. Assume is good and if you still have the old sending unit, test the fuel gauge. If needle moves, then look for problem in the wiring downstream. You can run a temporary new wire with alligator clips between the connector back to the sending unit at the tank. Run a ground wire from the sending unit to a good ground and see how everything works. It is a very simple circuit.

[chargerdon]

@dodj new to this what is the limiter and where is it? All my other gauges seem to be working fine.
@chargerdon  that was with the unit in the tank. Ground strap is on and I've even tried another ground to the frame and also one straight to the battery. Still didn't work.

Limiter is the device that changes the 12-14 volt supplied by the battery and alternator and reduces it to 5 volt as this is what the gauges need.   It supplies all three gauges, ie. the temperature, oil pressure and gas gauges.   So, if the other gauges are working fine, that means your limiter is also fine.   

OK, assuming you've got good ground at the sending unit, and at the tank it reads 32 ohms then check it right at the connector into the gauge it should read the same 32ohms or just slightly higher.   If it does, then the gauge MUST not be connected to the limiter correctly. 

If not then it must be the wiring thru the car from the sending unit.    That wiring goes up into the trunk into the wiring harness and then ends up at the kick panel on drivers side.  Take off kick panel and check it at the connector where it goes into the dash harness and to the gauge.   Check for the 32ohms at each place.   its a simple circuit.   

[DeathProofCuda]

Hope this is the right spot to post this. Replaced the fuel sending unit in my 71 Challenger. Gauge still isn't working. Tested the gauge with the batteries and it's good. Tested the wire to the gauge by grounding it and the gauge reads full so that's good. Tested the ohms on the sending unit. It reads 32 which it has just over a half tank so that's good. Regrounded it numerous ways and still nothing. Ran a ground jumper from bare frame to unit nothing. Got pissed ran a ground from the battery right to the unit still nothing. I'm at a loss here. What am I missing?

It seems like you've covered most of the standard tests here, but must have missed something.  When you tested the wire to the gauge by grounding it, how exactly did you do this test?  Were you grounding the wire connection that would connect directly to the sending unit, or were you testing it somewhere else?

If you were testing the connection right at the sending unit, then that should rule out a problem with the voltage limiter for your gauges.

Is this a standard or a Rallye dash?

[DeathProofCuda]

Just another thought.  The gauge cluster is grounded to the vehicle's electrical system through the screws securing it to the dash.  Therefore, if you are doing some of this testing with the gauge cluster partially removed from the car, like wired up but not screwed in place, then it causes problems with grounding for the instrument panel voltage limiter.

[dodj]

All my other gauges seem to be working fine.

Then don't worry about the limiter.
Make sure you have a ground wire clamped on the fuel line of the sending unit to body ground.

[Sparxx]

Standard dash. Have the ground going to the fuel line on the sending unit. Right where the ground strap is. Still nothing. Someone said use the old unit to test. The old unit is junk. The metal strap from the top of the unit to the fuel level float is busted and it's rusty. That's why I replaced it. This is driving me nuts. I just want a fuel gauge to work instead of filling up everytime I take it out.

[dodj]

Take the sending unit wire off the sending unit and jumper it to your sending unit ground strap. If the gauge pegs,  there is something wrong with the sending unit. If it doesn't, there is something wrong with the ground.

[Jay Bee]

Just throwing this out there. I could be way out in left field but thought it was worth the mention.

Maybe there's enough of a complete circuit for your meter to register the ohms BUT the grounding pivot point is not enough for your gauge to read. Ya know too much added resistance with car wiring and connectors.

Years ago I saw mention of this work around on another forum by adding a wire to the sending unit itself.

First picture is from that other site (which I edited), second one is my sending unit. 

[Mrbill426]

Hmmm... I wonder if this is what is going on with my fuel gauge.  I tested all the gauges when I had the dash out and apart using flashlight batteries as @Cuda Cody demonstrated in a video and everything worked fine.  New tank, new sender, new tightly installed ground strap on the tank fuel line.  I put probably near 10 gallons in the tank and it barely shows 1/4 tank on the gauge. 

Just throwing this out there. I could be way out in left field but thought it was worth the mention.

Maybe there's enough of a complete circuit for your meter to register the ohms BUT the grounding pivot point is not enough for your gauge to read. Ya know too much added resistance with car wiring and connectors.

Years ago I saw mention of this work around on another forum by adding a wire to the sending unit itself.

First picture is from that other site (which I edited), second one is my sending unit.