Oil alarm

[steplift20]

I'm mad, went down to go fishing. And this happened
Started her up,perfect
Drove her around ,no problems
Then after about a hour. I started her and the oil alarm
Went off.
Shut her down started her. Oil alarm went off ,so I took her back on land and and loosened the oil cap on the motor and it was pumping it into the oil resivoure ,so no issue with the pump
I did replace the cap/sending unit about three years ago.
What advice do you have for me? I'm going to go to my boat this week and check the cap/sending unit. After that I'm lost. Thanks for any replys

[spareparts]

Mercury?

[steplift20]

Yes spare, 1988 150 Mercury blackmax.
I know how to check the oil cap using a multimeter ,I'm just a hour away now from my boat and I did replace it about 3 years ago
The oil pump motion sensor. I do have my old one cause I did replace that too a long time ago, can you bench test the motion sensor? From what I see. The oil cap tells you if you have low oil
The motion sensor. Monitors the internal gear. So there are only too things left in case they check out good
The warning module. And the internal gear. But I'm not jumping to conclusions yet. If it's anyone of the last two I mentioned. Than I'm screwed. Just have to convert it to me mixing oil and gas but I don't know how to do that.

[steplift20]

One thing I forgot to mention, when you turn the key on it beeps than stops ( like it's supposed to do) then as soon as you start the engine it. Starts to beep with no delay. Just wanted to mention that.

[spareparts]

most likely the oil gear. You can check for voltage coming from oil pump sensor while the engine is running. If you aren't making any voltage, pull the oil pump, coupler and gear, shine a light in there and see if you see the gear. I've seen a bad sensor, a stripped coupler, and most of the time, stripped gear. Mix up a small tank of premix to run teh engine off of while testing

[steplift20]

Thanks spare,I will do that and let you know the results, but I really hope it's the cap.