engine noise on 1998 Infiniti Q45

Engine starts and runs fine after running a while engine noise starts sounds like valves or lifters then oil light comes on. Installed oil guage to check oil pressure and found 60 lbs at start up and then slowly dropped as engine warmed up.It dropped down below 15lbs and then oil light comes on. Turned off engine waited a couple minutes started it up again oil pressure was up and dropped down again. I removed valve covers and checked and cleaned out oil returns. They where not that bad with sludge. There is 90,000 miles on engine not a lot of miles. I am looking for direction to find problem.

by in Philadelphia, PA on October 27, 2010
2 answers
ANSWER by on October 27, 2010
clogged pick up screen in the oil pan or worn out pump. the pan will have to be dropped to see. a shop can do that for you. Roy
ANSWER by on October 27, 2010
Specification for oil pressure at idle is only 14 lbs at idle with oil at operating temperature, at 3000 RPM the pressure should be 67 to 81 lbs. Oil pressure switches frequently go inaccurate but that does not explain the noise. Mileage is low to have problems the engines are strong if the oil is often changed, have seen other electrical problems with that car. The engine uses hydraulic valve lifters, i wonder if you could have a "dirty" hydraulic lifter. Its hard to comment with out being able to hear the noise first hand or do some basic diagnostic tests.
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