Ok this is driving me nuts. My new RV7A has 20 hours on it, and everything is just lovely…except this darn oil pressure intermittent problem where the oil pressure gauge suddenly pegs off-scale high (data download shows 155 psi, in abrupt change from minutes of nominal readings)
Here is a description, and what I have tried:
First cropped up after ~12 hours on new engine:
Kavlico 150 PSI 3 wire sensor (GND, 5V, signal)
0.5V = 0 PSI
4.5V = 150 PSI
Mounted on transducer block on firewall. Plumbed to the engine with a restrictor valve on the engine side of the hose.
Gauge will read fine: 50-60 PSI during taxi, 70-80 PSI during runup.
It will react normally and then just suddenly jump to 150PSI+. When it jumps there, it usually stays there while I terminate the flight. After engine shutdown, it stays reading pegged 150 PSI+. After avionics power cycle withe engine off, it will sometimes show 150+ and sometimes clear the error and show 0 PSI. If it crops up, it likely crops up in the first 10 minutes after engine start. If it doesn’t crop up, I can fly for 2 hours (2 times) and not have a problem.
The 2nd and 3rd time it happened, I landed, quickly removed the cowl and wiggled wires near the oil pressure sender…no change. I separated the connector near the oil pressure sensor (3 lines) and measured 0V GND, 5.01V, and 4.5 V on the sensor return line (this is with sensor disconnected)…Also, seem to have measured 0V GND, 5.01V and 0V on the sensor return line sometimes when I disconnect it (each time i disconnect, I do see a change from off-scale high to red X on display)…this made me suspect the sensor return line was somehow shorting to the 5V supply, or that it has a pull-up resistor in the G3X GSU73 that is pulling high when the gauge is disconnected.
So I spent 2 hours, digging under the panel and disassembled the connector shell at the GSU73 and checked all wiring…the only wiring i haven’t check is if there is chafing where it goes thru the firewall pass thru since that is covered in fire seal. With the GSU73 connector removed, none of the 3 wires seems shorted to each other.
This leaves me thinking I should try replacing the $90 gauge. but this is weird failure mode right? Could this be a firmware glitch that is solved by G3X firmware update. Could this be an intermittent GND line? When the ground goes away the pull-up brings the line high and thus the off-scale reading?
I also plumbed a mechanical gauge in parallel with the G3X Kavlico sensor, and the readings during a full runup are within 1-2 PSI from 0 to 50 to 80. But, since it seems i need to fly to get the glitch, I haven’t had the mechanical gauge plumbed during any of the actual glitch events. But I’m convinced it is not a real pressure event and it gauge or wiring…
Why would sometimes an avionics power cycle clear the error and return it to 0PSI if it was a wiring problem?
Any ideas would be much appreciated.