For some reason, I thought the sensor measured oil pressure. I have a 20 hp kohler that I'm sure it's sensor measures pressure, because every time I change oil and filter, it takes a few more cranks before the engine makes a spark. Once I goofed, pulled the choke to start the enging after changing oil, About 10 cranks later the spark arrived and shot fire out the muffler. One BIG BANG.
Because the 390 doesn't have an oil filter, you may be right. What tells the sensor there is the presence of oil if it doesn't use pressure?
You're right, it takes a lot to crank a 390. My right arm is still hurting.