Debugging the fuel gauge.

[Valkman]

Ok  my fuel gauge isn't working right,  and since the the filler neck seal was leaking l desided to pull the gas tank.  I pulled out the sending unit (which looks pretty new) and test the resistance.  It read about 67 ohms empty and about  9 ohms at the full level. The other gauges seem to be working properly so I think the dash voltage regulator is working good. I then hooked up the sending unit and dry tested it and here's what I found.

Set at empty the needle disappears.

When set at full the needle moves but seems to hit a mechanical stop right before the E.

Could mean the needle is in the wrong position?

[Cuda Cody]

@Valkman  is sounds like the fuel gauge is having some issue.  Not sure if this will help, but I made a quick video on how to check fuel gauges.  Good luck and let us know what you end up doingto fix it.

[Valkman]

Thanks Cody, I've seen that video, it was a great help, it got as far as I got to this point.

I don't want to have to pull the dash apart if I don't have to, but it looks I might be forced to.  If I do can anyone tell me how to inspect the gauge itself?

[1 Wild R/T]

Before you take the dash out... Go to radio shack & pick up a few resistors....    Disconnect the wire from the sending unit & use a resistor between that wire & ground...  10 Ohms should register a full tank...  90 ohms should register an empty tank...   

You should be getting a pulsing power signal through the sending unit lead with the key in the run position.... With an old analog gauge you should read about 5-6 volts... A digital gauge reads to quickly & you'll have a tough time getting a usable reading because the IVR pulses the power to lower it to the 5-6 volt range... 50% duty cycle = 50% of the full voltage...

[Valkman]

Before you take the dash out... Go to radio shack & pick up a few resistors....    Disconnect the wire from the sending unit & use a resistor between that wire & ground...  10 Ohms should register a full tank...  90 ohms should register an empty tank...   

Since I checked the resistance of the sending unit it's that doing the same thing?

When needle raises it comes a very hard stop you can actually see it bounce a little when it does like the travel is being mechanically limited

[shawge]

Is there a ground strap between the sending unit and the fuel line?

[Valkman]

Is there a ground strap between the sending unit and the fuel line?

Yes, when I ran the test I made sure it had a good ground.  The needle moves so it's get a signal.

[Cuda Cody]

Sounds like the gauge is broke.  It should sweep smooth and not have any hiccups or get stuck.     

[Valkman]

That's pretty much what I'm thinking.  One thing I did notice is that the gauge needle disappears  (see 1st photo ), when I was looking at replacement gauges the needle rest on E. Do you think it's possible the needle is out of position?

[Cuda Cody]

Maybe?     It should be seen all the time and not disappear.   

That's pretty much what I'm thinking.  One thing I did notice is that the gauge needle disappears  (see 1st photo ), when I was looking at replacement gauges the needle rest on E. Do you think it's possible the needle is out of position?

[RUNCHARGER]

I agree, something is wrong with the gauge. It sounds like something has slipped out of place. The needle should not disappear and it shouldn't hit a stop in that position.

[1 Wild R/T]

I agree, something is wrong with the gauge. It sounds like something has slipped out of place. The needle should not disappear and it shouldn't hit a stop in that position.

Agreed... But the sender is out of proper range too...  67 Ohms means when your out of fuel the gauge will be reading close to 1/2 tank...

[shawge]

Aren't the Mopar gauges calibrated for 70 - 10 ohm?

[1 Wild R/T]

Aren't the Mopar gauges calibrated for 70 - 10 ohm?

Actually 73-10........  I was thinking of Ford which is 90-10....  Sorry old & simply wrong...

[RUNCHARGER]

Yes, there is a ground strap from the sending unit to the body fuel line.