Re: 1994 mercruiser 7.4 oil pressure question
plumb in a mechanical gauge to see what the motor actually has for oil pressure. then troubleshoot your gauge and sender
BBC engines make a heck of a valve train racket if there is no oil pressure. If his engine was quiet, then I suspect the oil pressure is present. Even if it is the minimum needed to run the engine and I'm pretty sure the '94 had the low oil pressure warning buzzer (my '92 does), which would have singing loudly if there is no oil pressure.
The trouble shooting guide I sent can mostly be done w/ out engine running.
To JSWeeden.... You'll need 12 VDC on the gauge to test it. If you have a 120 volt to 12vdc power supply handy, even a little wall plug type, you can test the gauge sitting at your computer desk, using the power supply, just like your boat's electrical system. Just make sure the + and - are connected correctly. Just need to have a little "Mc Giver" in you to do some things, sometimes.
If everything checks out OK and still no indication of pressure, then yes, the mechanical gauge would certainly be my next step. But I bet he'll find an electrical problem 1st. As normal oil pressure is 30 - 70 PSI on these engines (Mine holds right on 40 PSI at all times from idle to WOT, hot or cold) and believe it or not, 4 PSI is absolute minimum at idle w/ engine hot (factory spec), seems as though any oil pressure at all will keep engine fairly quiet.