Fuel Sending Units and A-Body Fuel Tank Map
There are two Main Reasons that Aftermarket fuel sending units do not give accurate fuel level readings.
The first and most important is that the wire-wound variable resistance board on the stock sending units are shaped and wound for the tank that it was intended to be used in.
Therefore the resistance levels are not linear from end to end. Empty is somewhere around 73 ohm and Full is somewhere around 10 ohm with the in between readings changing in Non Linear steps.
Stock Non-Linear Board
The aftermarket sending units have wire-wound variable resistance boards that are a simple rectangle shape and wound so that they read somewhere around 73 ohm for Empty and somewhere around 10 ohms for Full with the in between steps going up in a linear manner.
The aftermarket sending units will never give a correct fuel level indication.
Aftermarket Linear Board
Non Linear Linear Fuel Sending Unit Difference
The other reason is that the float arm lengths are not correct for the tanks they are used in.
I have made a map of fuel levels in an A-Body fuel tank and a holding fixture which positions a sending unit at the correct height as if it were in a fuel tank.
Here are photos showing a stock sending unit and a aftermarket sending unit for comparison.
Stock Sending Unit
Aftermarket Sending Unit
You can see that the stock float is at the correct Full position while the aftermarket float reaches its Full position at about 5/8 of a tank.
Now you know why it seems to take forever for the fuel level to drop and then go quickly to empty.
I am and have been working on a calibration unit that is similar to the MeterMatch.
The calibration unit I am working on has a total of 11 set points. There are 9 set points from Empty to Full in 1/8 tank increments and 1 set point for a Low Fuel Alert(Steady On LED) and 1 set point for Low Fuel Alarm(Flashing LED)
Once all the set points are programmed, the reading are interpolated for a very smooth and accurate meter movement.
I am not yet ready to market or produce these units. They are in the testing mode and I need to figure out how to set up an LLC before I do much more.
Herb
There are two Main Reasons that Aftermarket fuel sending units do not give accurate fuel level readings.
The first and most important is that the wire-wound variable resistance board on the stock sending units are shaped and wound for the tank that it was intended to be used in.
Therefore the resistance levels are not linear from end to end. Empty is somewhere around 73 ohm and Full is somewhere around 10 ohm with the in between readings changing in Non Linear steps.
Stock Non-Linear Board
The aftermarket sending units have wire-wound variable resistance boards that are a simple rectangle shape and wound so that they read somewhere around 73 ohm for Empty and somewhere around 10 ohms for Full with the in between steps going up in a linear manner.
The aftermarket sending units will never give a correct fuel level indication.
Aftermarket Linear Board
Non Linear Linear Fuel Sending Unit Difference
The other reason is that the float arm lengths are not correct for the tanks they are used in.
I have made a map of fuel levels in an A-Body fuel tank and a holding fixture which positions a sending unit at the correct height as if it were in a fuel tank.
Here are photos showing a stock sending unit and a aftermarket sending unit for comparison.
Stock Sending Unit
Aftermarket Sending Unit
You can see that the stock float is at the correct Full position while the aftermarket float reaches its Full position at about 5/8 of a tank.
Now you know why it seems to take forever for the fuel level to drop and then go quickly to empty.
I am and have been working on a calibration unit that is similar to the MeterMatch.
The calibration unit I am working on has a total of 11 set points. There are 9 set points from Empty to Full in 1/8 tank increments and 1 set point for a Low Fuel Alert(Steady On LED) and 1 set point for Low Fuel Alarm(Flashing LED)
Once all the set points are programmed, the reading are interpolated for a very smooth and accurate meter movement.
I am not yet ready to market or produce these units. They are in the testing mode and I need to figure out how to set up an LLC before I do much more.
Herb