another gas guage question

[nrubino]

I have a 67 cuda with a rallye dash, brand new gas tank and sender.
Gas guage reads past full when i turn on key, I know I only have about 11 gallons in it.

what are some possible reasons for this? It does not have an external voltage limiter.

Thanks, Nick

 

[67Dart273]

First thing to do is "split" the problem. How do you know the "rest" of the gauges are accurate?

Could be gauge unit not accurate, or voltage limiter (it's in the fuel gauge, but you DO have one)

Could be the sender is old and sticky, or has been replaced with a Chineseo repop which have a habit of being less than great.

Or if running, the system voltage could be way hight

Start by going to Radio shack and getting some resistors

All gauge senders are same resistance, oil, temp, fuel

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

so if you buy four 100 ohm, 1/2 watt resistors, and wire all four in parallel, this gives you one 25 ohm resistor. Wire that from the tank sender wire to a good ground, and leave the key on for about a minute. The gauge should read 12 tank. If so, the gauge, and the voltage limiter are at least reasonable accurate

 

[RedFish]

Way past full is zero resistance or shorted to ground. This will kill the gauge.
First thing I would do is disconnect the rearward harness connector behind the left kick panel. If the gauge stops working completely the problem is from that cannecotr rearward. First place I would look for a short in that drk. blue wire inside the trunk.
If the gauge still goes to max after harness disconnected the problem is from that connector forward.
Pull the instrument panel and search from that printed circuit board connector and downward. The dk blue in question is at the 12 o'clock position.

 

[nrubino]

I will try these things, thanks!