How to test sending unit wiring connections
Moving to the fuel tank, inspect the top of the fuel sending unit for any damage and/or corrosion, and that it is seated correctly in the tank. If the top of the unit is dirty, take the time to clean the connectors to help conductivity. Make sure there is a good ground connection as well. To verify the fuel sending unit is receiving proper voltage, set the multimeter to 20 volts. With the battery turned on, back-probe the input connector on the sending unit and check for voltage. Refer to the Service Manual for proper voltage. If the input voltage is lower than volts called for, inspect the wiring from the sending unit to the battery as it could be faulty.
Checking the output voltage, measure how much voltage is being sent from the fuel sending unit to the fuel gauge. The voltage should measure the same on both ends of the wire. If the voltage is different, there is corrosion or poor wiring between the sending unit and the gas gauge.
Fuel systems are fairly simple as a whole; a pump send fuel through the lines, which feed the carburetor or fuel injectors. However, in the midst of that simplicity lay a number of different components that make it all happen. It all starts with an understanding of some fuel system basics.
A fuel sending unit doesnt “send fuel” as its name implies; it sends an electrical signal from the fuel level sensor to the fuel gauge. Only cars that use electronic fuel gauges or fuel injection computers utilize a fuel sending unit.
Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.
Fuel pumps come in two basic varieties: in-tank and in-line. Most fuel-injected cars use a high-pressure in-tank fuel pump that pushes fuel through the lines from inside the tank. In-line pumps sit outside the tank but near it and usually below it, and provide a low-pressure flow of fuel to keep the carburetors reservoir full.
How a fuel sending unit works
The fuel sending unit located in the gas tank to measure the fuel tank level. Some sending units are attached to the fuel pump assembly, while others are stand-alone units, but both are made up of the same three components: a float, a metal rod/arm, and a variable resistor. These three components work together to measure the vehicle’s fuel level and relay the information to the gas gauge.
Float – The float, which is made of a buoyant composite or foam, floats on top of the fuel in the tank.
Metal rod or arm – The float is connected by a thin metal rod to a contact inside the variable resistor.
Variable resistor – A resistor is an electrical device that resists the flow of electricity, and a variable resistor has the ability to adjust the amount of resistance voltage encounters by sliding a contact (wiper) over a resistive element. The wiper is connected to the fuel gauge either directly by wire, or indirectly to an electronic device that communicates with the fuel gauge. In a fuel sending unit, the variable resistor receives power via a small coil from the vehicle’s battery, which is used as the baseline signal.
The fuel sending unit is one of many terms associated with this auto part. Some other terms used include: sending unit, fuel sender unit, fuel tank sending unit, fuel level sender unit, fuel level sending unit, fuel pump sender unit, fuel pump sending unit, fuel gauge sender unit, fuel gauge sending unit, and fuel level sensor. Luckily, these names are interchangeable because they all refer to the same part with the function of measuring a vehicle’s fuel level.
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