Cadillac Seville / Cadillac Eldorado Forum Discussion, A few quick questions in Past Cadillac Vehicle Discussion; 1. There is something that looks like an O-ring hanging on the end of the oil-filler neck. What is it, ...
Take off the beauty cover and check your PCV piping: The PCV valve itself is in the rear cam cover and leads to a nipple in the intake manifold behind the power steering pump. The connector in your picture is the PCV system fresh air supply and should go to a connector on the upstream (clean air) side of the throttlebody. BTW, all PCV valves are not alike: different part numbers have different flow rates, so you must use the one calibrated for your particular engine.
The O-ring on the oil fill cap seals that opening, and, believe it or not, is a potential vacuum leak and also upsets the PCV flow rates.
Check the O-ring on the oil dipstick also - another potential vacuum leak.
With varying blowby rates depending on engine rpm and power demand you would think a small air leak into the crankcase caused by one of the two O-rings mentioned would be inconsequential: It is not, as the PCV flow at idle and part throttle is part of the air/fuel ratio equation maintained by the MAF, IAT, and O2 sensors.
After 2000, some Northstars do NOT have PCV "valves": they use a fixed orifice nipple in the rear cam cover and it is not removable. Clean them with a fuzzy pipe cleaner soaked in throttlebody cleaner.