mileshoover said:
I, too, wonder about the very low idle figure given.
I know this thread is probably dying but I do have one last thought to share.
The numbers out of the Service Manual are "specifications" and the 4psi is specifically called out as a "(min)". Some bright engineer at DC has figured out that at 4psi there will still be enough oil flow to the engine to prevent serious damage. 4psi is equivalent to approximately 9 feet of pumping head. This means that with 9 feet of available pumping head you should have at least some flow to the top of the engine which is, at most, 2 or 3 feet higher than the oil in the oil pan. When oil starts flowing you get additional pumping head from line friction, etc. When you get 6 or 7 feet of this additional head, there should be enough (ie., "min") flow - according to the specification.
My guess is the oil pump, in good condition at maximum rpms, puts out something like 120-160 psi (pretty typical of an inexpensive single stage centrifugal pump). A lot of this pressure is lost pumping thru the oil filter bringing you down to the nominal 35-110 psi for delivery to the engine at 3000 rpm, a "typical" operating condition. There's a big range here because a lot may depend on the condition of the oil and oil filter. The 3000 rpm specification sets both a minimum and a maximum. If you've got more than 110 psi, it probably means there's a line plug on the downstream side of the filter - a potentially disasterous situation. If you've got less than 35 psi it could mean a lot of things: your pump could be wearing out or broken, your filter might need replacement, your oil could be the wrong weight, your oil could be non-existent

. At idle speed, the pump will generate less pressure (but way more than the 4 psi "min") and less flow (but way more than what you get at 4 psi "min").
Hopefully (I'd almost stake my life on it -- well, maybe not

) the oil pressure sensor is located at a point in the oil line
after the oil filter. Otherwise, if the filter were to become seriuosly clogged, you could be showing plenty of pressure when in fact there was little or no available pressure (and consequently, no oil flow) on the downstreem side of the filter.