I am currently building a custom arduino powered gauge system for my AE86. The only portion of the original Toyota designed system that will be carried over are all of the sensors. In order to have accurate readings, I need a calibration curve of all the various sensors. The temperature sensors being simple thermistors are easy. The oil pressure sender, however, is being a pain. According to the schematics, voltage flows through the sender and straight to the gauge cluster. Typically with setups like this, the sender is varying its resistance relative to pressure which causes a current change finally deflecting the meter needle. It doesn't appear to be operating in this fashion however.
First off, I am using a new, never installed sensor from Beck Arnley and all pressures stated are in psi absolute. I have the sensor currently connected to a Druck DPI620 Genii pressure calibrator. I have connected the Druck's ohmmeter to the sensor case and the brass post. At atmospheric pressures (14.2 psia around here) the resistance is infinity. Once I begin applying pressure, the reading stays at infinity until almost exactly 19 psia where it begins fluctuating wildly. At first it appears to want to be 500 ohms but it eventually settles around 50 ohm. Continuing further up the pressure scale in 5 psia increments, the readings all stay within 10 ohms of 35 ohms until the sensor locks at 35.7 ohms around 40 psia. Multiple runs up and down the scale produce different values so, as tested, this thing has terrible repeatability. It sounds like it is acting as a pressure switch, but I was very careful in sourcing the gauge sender and not the dummy light switch. It is the large gold mushroom canister style sensor I've seen posted on here many times. So what I need to know, is how, exactly, do these sensors operate? Are they potentiometer style, bimetal spring diaphragm types, strain gauge transducer type, or something else? Also, what is considered the nominal oil operating pressure for a freshly built 4AGE? On most of my other non-performance vehicles, 40 psig is typical.
Thanks! For the curious, I'll make a post with the completed gauge system once it is final. Don't hold your breath though. I started this LAST June and it's still not finished because real life sucks. I doubt I'll be able to produce them in any kind of quantity either so I guess it'll be unique anyway
