Need help with gas gauge .

[Street fighter]

I have a 73 dodge charger that have a problem with the gas gauge. It works but it goes all over the place unless I put about 5 or more gals. in it than it stays on full until it runs the gas down to a point, than it goes back to the moving from empty to whatever it decides to do. I have installed three new sending units hoping that they were bad, but I still have the same problem. I have been working on this problem off and on for two years. I was thinking it was the gauge itself or the voltage limiter located behind the dash. can anyone help with this problem? each time I drive the car my frist stop is to get gas because I don't trust the gauge reading.

 

[Dako]

You likely have a grounding issue.

The sending unit grounding path:
- the grounding strap...that little 'clip-like' thing going from the sending unit to the main fuel line.
- the main fuel line to the clips that attach it to the cars body.

Since you are getting 'something' on the gauge, I assume you have the grounding strap on. But if there is rust on the line; those clips that hold it to the body; or the holes where the clips go into the body, you will not get a good ground. You may get lucky by simply popping the line out, and then back into, one of the clips.

 

[Street fighter]

I though the same thing, so I grounded the sending unit to a part of the frame,Tested it for ground and I do have one.

 

[Bolt-Action]

Have you checked the wires on the gauge itself?
may not be a bad idea to substitute in a cheapo aftermarket gauge to see if you get the same results.

 

[kiwigtx]

If you had only tested the one unit, I would have suggested the float had a pinhole and was full of fuel.
But since you get the same results from 3 x different units...that is not the problem.

The Fuel and Temperature gauges are both fed from the voltage regulator - so either both work, or not.

It actually sounds like the gauge is not sitting at the correct angle inside the tank. If it were cocked to one side, this gauge irregularity would occur. Make sure the filter sock sits on the bottom, and the gauge arm goes up & down vertically...not an angle.

 

[Street fighter]

Have you checked the wires on the gauge itself?
may not be a bad idea to substitute in a cheapo aftermarket gauge to see if you get the same results.

I got the same results with a after market gauge I tried.I am just about ready to give up on this issue, like I stated in my frist post I have been at this for 2 years off and on.

 

[Bolt-Action]

Don't give up,
it's usually something pretty easy and its usually the last thing you check (that's how it usually works for me lol)
question, are you running the orig gas tank, how does it look inside, I'm not familiar with the 73's but does the sending unit only go in one way or can it be "clocked", also, out of curiosity, how are your return lines and what cap are you using?

 

[Dennis H]

I gave up. Write down the mileage. Gas every 150 and flirt with 200 miles on a road trip. New tank, sending unit, check grounds etc. Won't go past 3/4 when full. Bend this, try that. No luck.

 

[Street fighter]

I gave up. Write down the mileage. Gas every 150 and flirt with 200 miles on a road trip. New tank, sending unit, check grounds etc. Won't go past 3/4 when full. Bend this, try that. No luck.

That's just about where I am right now,I love driving the car but with this gas hand going from full,to empty than where ever it decides to land. I don't know if I have enough gas to go where I want to go or not. buying gas every time I pull it out to drive it is getting old fast.

 

[Chickenman21]

I'm a little late on this thread but you may check the connection at the sending unit. I have found that the rubber boots on the wire can become hard with age and not make a secure connection. I cut off the boot and put on an eye connection and install on the sending unit with a small nut / washer. I also drill a small hole at a corner of the tank and outside of the seam and run a second ground to the frame.
Hope that helps.

 

[bigaadams]

the fuel gauge and the temp gauge share the same CVR..if the temp is good you got a gas circuit problem..it is not recommended to directly test the sender to ground and the use of a 73 ohm resistor (+/- 12 ohms) is advised to hold the guage at empty mark and not below. (needle width of the line either side is the avg fudge factor) The use of a 10 ohm will hold it at the full mark. If this test fails you have possible wiring or gauge issues. If passes, would recommend pulling the sender and test for smooth swing of display of ohm reading on an ohm meter..again, (9.6 to 73 ohms avg reading) check the float for pin holes as recommened above also..sometimes the wiper on the sender resister gets worn..careful bending and cleaning of the wiper arm can again put some tension back to the wire wound resistor and get you back to reading proper. This is not a hard circuit to test or repair.

again...quick test using 10 and 73 ohm resistors with sender in tank using resistor between guage wire and ground at tank plug....
sender test, pull and evaluate smooth operation and minimum 9.6 ohms at Full and 73 +/- 12 at Empty.

else grab a Mopar tester C-3826

 

[bee71]

You may want to check and see if you have the proper gas cap. 72 and up had a different one than 71s and older.

 

[cbunt1]

....
sender test, pull and evaluate smooth operation and minimum 9.6 ohms at Full and 73 +/- 12 at Empty.

else grab a Mopar tester C-3826

Not trying to hijack the thread, but I'm working on my fuel sender as well -- looks like my gauge is good as is my ground -- getting around 80 ohms from the sender (indicating empty tank), so I think I have a pinhole in my float. Of course I proved this by filling the tank and taking a reading

Question is -- how long are these sending units -- i.e. is there enough clearance under there to pull the sending unit without dropping the tank?

 

[kiwigtx]

It is also possible that there is a problem with the wire running from the gauge to the sender unit (normally blue), and if it is shorting to the body periodically, it will cause these wild fluctuations on the gauge.

Easy way to test is to run a separate wire between the gauge and the sender and see the readings. Try to connect in a semi-permanent manor, so you can test drive the car. If that works OK, then you need to replace the entire length of cable between gauge and sender - tedious I know, but if there is a problem, these are the sorts of things you need to try out.

Good luck, and let us know how it goes.

 

[Street fighter]

I have a voltmeter but I have no ideal how tuse it.

Not trying to hijack the thread, but I'm working on my fuel sender as well -- looks like my gauge is good as is my ground -- getting around 80 ohms from the sender (indicating empty tank), so I think I have a pinhole in my float. Of course I proved this by filling the tank and taking a reading

Question is -- how long are these sending units -- i.e. is there enough clearance under there to pull the sending unit without dropping the tank?

I have a meter and have tried to use it but have never used the ohms to do anything. just how do I do what you are telling me to find out about the sending unit or gauge.

 

[cbunt1]

I have a meter and have tried to use it but have never used the ohms to do anything. just how do I do what you are telling me to find out about the sending unit or gauge.

It helps to have some idea what your fuel level is, of course, (full, 1/2, 1/4, etc.). On the sending unit is a signal wire (right next to the outlet pipe) -- Set your meter for 100 Ohms, and make sure the meter is calibrated (assuming analong) (Jumps to full-needle when you touch the probes together). Take a reading between the signal wire output (on the tank) and the tank itself (or the outlet pipe--whatever you can get to easily). An 80-ish ohm reading is an empty tank, and a 100+ ohm reading is a full tank.

It's more of a quick and dirty check to see if your sending unit is putting anything out...

Does this help? I can pull up some better descriptions from the FSM if you need...