Gas Gauge very inaccurate.

[Mr.FT]

My gas gauge on my 72 Demon 340 is not linear by any means. I filled the tank, Gauge read full also. I drove home @ 24 miles and gauge read 1/2 . Went to local cruse night @ 4 miles Gauge reads 1/4. I filled the tank and it took @4 Gal which really threw me but the gauge read full again. Is this normal?? If not Where should I start, Sending unit, gauge or other.

Thanks
PS: Everything I read says these have @ 16 Gal. tank.

 

[67Dart273]

This has been covered here a bunch do some searching

There are a few places for inaccuracies.

First, does your temp gauge read accurate, that is, have you actually checked it against a known thermometer?

So the general problems can be, in no real order

1...worn out stuck rusted etc tank sender OR A "repop" which have very poor track record

2...Wiring bad connections. The tank, the kick panel connector, the cluster connector

Connections on the cluster PC board

3...Inaccurate cluster voltage limiter

4...Poor connections at the gauge stud nuts on the cluster board

5...Gauge damaged worn old "out of tolerance."

====================================

Where to start? There "used to be a tool" in the shop manuals. This is basically a switchbox with three resistors inside, to check senders / gauges for empty / cold--------for mid scale-----and for full / hot at high end of scale.

They seemed to have been.....

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

So you need to "come up with" those resistors to test the system. This used to be easy.......until RadioShet went downhill. so now try Mouser or Digikey. You probably need 1 watt resistors.

Even without the resistors you can estimate if the gauge is correct. Look at the above resistance.........if you can warm the car up until the temp sender says about 73 ohms, then hook up the gauge to the sender again, with key in "run" and let it sit a minute, the gauge should read close to the "cold" pin. Likewise, at about 23 ohms, the gauge should sit in the middle of the scale.

Likewise the fuel. If you can devise a means of attaching a test resistor to the sender wire, you can see what the gauge is doing.

You can also fill and empty the fuel tank and measure sender resistance for empty, for 1/2 and for a full tank.

THIS ISSUE IS A BIG problem with guys on here. Much of the issue, to repeat, is poor quality replacement (repop) gauge senders.

Also "there was a guy" making a calibration unit.......

http://www.forabodiesonly.com/mopar/showthread.php?t=264543

and here

http://technoversions.com/MeterMatchHome.html

 

[Mr.FT]

Can you recommend a Good or Better replacement sender if that is the problem?

 

[67Dart273]

No. Only thing available are the "repops" and if there's any of them better I don't know

Only alternative is to fix your old one, find a good used one, or "luck out" and find a NOS.

I've been wanting to try the calibration unit I posted earlier, but my car is "down for paint"