Deve: I read through your Fuel System documentation and have a question. You say the Standard Motor Products PS133 completes the circuit when oil pressure is 12 PSI or above. Specs for the GMC 228 engine (I don't have Chevy 216 specs) call for at least 5 PSI at a hot idle when newly rebuilt and at least 2 PSI at a hot idle when well used. Using my 228 as a real world used example, hot idle oil pressure is around 10-12 PSI. It would seem to me that this 12 PSI switch may shut off the pump at idle. Your comments are certainly welcome.
The 216 and all Chevy stuff runs at about 20-40, so maybe that PS133 won't work for you. I have no idea on GMC engines. If you have a very badly worn 216, I can see it being a problem too, but that's the time to re-shim the rod and crank bearings. An old mechanics trick is to use Reynolds Heavy Duty Aluminum Foil. If you find a lower pressure switch, please post that number. Good observation. I wish my knowledge extended to GMC more.
