Oil pressure sender testing

[cclxxxz]

Does anyone know how to test an oil pressure sender (not a switch)? My truck is a 1993 4-cylinder 4x4. Is there a chart of pressure vs. electrical resistance for the sender? Mine measures 50 ohms with the engine running (at any rpm) and open with the engine off.

Please help!!

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Check your service manual.
When you measured 50 ohms. Had you just started the engine and revved it a few times? That wouldn't really cause the pressure to change significantly. Try actually driving it around for a couple minutes (with a heavy foot) to build the pressure up, then test it to see if the value has changed.
If it still hasn't changed, that you might be testing the pressure switch instead.

[cclxxxz]

The 50 ohm reading has not changed in over 50 miles. It is the same reading I got when I pressurized the sender with air at 20, 40, 60, and 80 psi.

I have checked the service manual. It doesn't provide a chart of resistance vs. pressure. It says to connect a 12-volt battery to the sender with some sort of LED test light in the line, and make sure that the frequency of light flashing changes with rpm. That's pretty much useless.

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Originally posted by cclxxxz
I have checked the service manual. It says to connect a 12-volt battery to the sender with some sort of LED test light in the line, and make sure that the frequency of light flashing changes with rpm. That's pretty much useless.

Did you try that? What happened?
Obviously it means that this sender works by varying frequency. So something like resistance or voltage will never change.
If you have a good voltmeter, you should be able to set it to measure Hz. That would save you the trouble of setting up the strange apparatus as you described.