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Hi, I have a 1973 Pontiac Laurentian/Chevrolet Impala. The problem I have been having with it is; when my gas gauge gets down to the 1/4 tank mark, it will not go any lower than that. I have actually ran out of gas when the gauge claims that I have a 1/4 tank left. Any insight/help is greatly appreciated, thank you.
 

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I imagine the little arm that the float is on is binding. You could drop the tank, pull the sender and fix it.......or just put gas in it when it gets near 1/4 tank....which BTW is better for the car.
 

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could be the float arm is bent, and hitting the bottom of the tank to early..

do some testing with a ohm meter on the sender, but normally you do have to drop the tank..
 

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1949 Ford Coupe RESURRECTION
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Not to seem disagreeable but I'll bet you that there is a cover plate in your trunk with a couple of screws in it that you can take off and get access to your sending unit without removing the gas tank. In addition if you're sending unit and gauge
are the bi metal "warm up" types you can usually fool the gauge with a resistor to ground on the sending unit. that's the type of gauges that are on my 49 Ford
 

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Probably high circuit resistance somewhere.Most likely the sender....BUT

Here how it works:

When the sending unit float is on top (full tank) the gauge reads full. As the fuel in tank lowers , so does the float arm and consequently so does the sending unit resistance. When the tank is empty, the resistance should be low, like close to 0 Ohms.

NOW....if the resistance wire (In the sender unit itself) is cruddy/dirty then the resistance will be higher than normal , resulting in a higher than correct reading on the gauge

If the connection at the sender, or the tank ground wire, or its connection to the frame (Ground) has high resistance , it will cause a Higher than correct resistance for the circuit and the gauge will read too high.If that checks out OK, then you have higher than normal resistance in the unit or its associated wiring/ground/ connections

A fast way to check the wiring to the gauge is to pull the wire at the sending unit and ground it.The gauge should go to empty.If not, the gauge ,or the wire from the cluster has a problem.Be sure you have a GOOD connection when testing so you get correct results

There is no removable panel to get to the unit, so you may have to pull the tank, or at least drop the front of the tank down a few inches to get the sending unit out.
Chances are more likely that the unit itself has a problem, but clean the ground connection and the connection at the sender first to rule that out.

The unit should have its own ground wire affixed to it. Be sure the connection is good and clean, not rusty or corroded.
When I installed my new sender I soldered the crimp connections to keep corrosion down.I used a mostly tin/no lead solder with rosin core.
 
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