Naively, I though that I could remove the valve from beneath the car. Nope! To get it off, I had to remove the air filter box, the oil filter, drain the sump, remove both the filter adapter plate and relieve valve return hose (along with the sump spigot that the hose attaches to), cut the frozen clamps on the hose, and then unscrew the relief valve. While I was at it, I also removed, inspected and cleaned the bypass valve. I was encouraged when I found a small piece of metal swarf sitting in the seat of the relief valve. I think that you can see what looks like a tiny o-ring at about 7 o'clock down in the valve seat.
Eureka! That explains it! I cleaned everything up, made new gaskets for the adapter and sump spigot, put everything back together and refilled the engine oil. To my disappointment, the pressure is as bad or worse than before. Now, it struggles to reach 40 lb. at 2700 rpm (hot) and at idle drops down close to 0. Unless someone has a better idea, I guess my next step is to install a mechanical pressure gauge and see what I'm really getting. If those readings are indeed accurate, how can I tell whether the problem is with the pressure relief or bypass valve, oil pump, or, heaven forbid, big end bearings?
