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No way to accurately test the sender. You can test the gauge without removing it from the panel providing your other gauges are working correctly. All the gauges work on a nominal 5 volts and 10 ohms high reading and 73 ohms low reading. If you can get a 10 ohm and a 73-ohm resistor you simply connect the resistors in place of the sender and turn on the ignition. + or- an ohm or two won't affect the reading. Using the resistors every good gauge I've tested lined up within a needle's width of the high and low marks.
Crop Duster,
I am new to this, so I have a question. Using your "devices" I would remove the wire from the sender, clip one end to the wire and the other end to ground, simulating the resistance of the sender. is that correct?
Yes, that is correct. Disconnect the sender and put the resistor in the circuit. The resistors will work to test any of the gauges as all the gauges work the same just the faces are different to depict what they are measuring.
Yes, that is correct. Disconnect the sender and put the resistor in the circuit. The resistors will work to test any of the gauges as all the gauges work the same just the faces are different to depict what they are measuring.
You can check the sender as well. Disconnect the gauge wire and measure the resistance to ground from the sending unit lug. It will at least get you close. You should measure about 73 ohms without the engine running and 10 ohm at mas pressure. One source indicated it would be 10 ohms at 90 psi. Start the engine and measure the resistance and record the pressure you get from the gauge you installed. The resistance will change linearly with pressure so you should be able to see if the resistance matches the indicated pressure. Also confirm that the sending unit case is grounded to engine ground. Sometimes the use of teflon tape on the threads will not provide a complete ground and you will get false readings.
Sometimes the use of teflon tape on the threads will not provide a complete ground and you will get false readings.
Good point! I wasted quite a bit of time tracking down what I thought was a bad gauge, and/or sensor, in my '92 F150 years ago. Turns out it was my fault, as I used too much teflon tape on the sender.
I followed Crop Duster's and GPatrick's suggestions which lead me to buying a new sender unit. Once it was installed, the factory oil pressure gauge has some "range" now that I can relate to the pressures I got earlier on the mechanics test gauge. Thanks all.
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