when cruising at operating temp, say 1500+ rpm, i see about 20-30psi...40psi WOT @ 5500...but when i come to a stop light and idle (800-1000rpm) the pressure drops down to 5-7psi (which turns my fuel pump off cause i have it wired to a oil pressure switch)

what can cause this? i changed filters, went to a thicker oil, the oil seems clean, no odd noises like spun bearing or anything, compression is fine on all the cyl's...last thing i can think of is the oil pumps pressure valve is stuck open...i really would like to exhaust all options before i tear into the motor to replace the pump.

 

it is probably not the pump. if the relief was stuck, you wouldn't get anything, let alone 40psi. i guess it could be the actual pump itself (gears, housing), but if it does have that kind of wear you probably need a rebuild anyway. really hard to say anymore without knowing more history on the engine. grasmo.

 

i do have an intake manifold oil leak...but i highly doubt that would bleed off so much pressure at idle.

 

well i would say you are correct. the manifold is not in the pressure circuit. the oil you are seeing is from splash or windage. generally the oil will chase the threads of the manifold bolts creating the leak appearance. now if your leak is at the back then it could be a leak at the sending unit or the gauge ferrule depending if your gauge is electrical or mechanical therefore you would have a pressure drop. grasmo.

 

its an electrical guage...ive switched from a mechanical one a day ago, same readings. the pressure is alright up until the car warms up to temp.

the only leaks i really have are the front/rear of the intake manifold, and part of the valve cover on the drivers side. it is a junkyard motor...maybe the bearings are just worn. wish there was an easy way to check this though..even in an RX7 i have a bit of a time dropping the oil pan