|Adventures Under the Hood|
The PCV system is simple, and has nothing to do with the computer. A manifold vacuum fitting at the rear of the BBD pulls fresh air through the crankcase and out through the PCV valve into the intake manifold, where any vapors are burned instead of escaping to the atmosphere. This reduces pollution and helps prevent sludge buildup inside the engine.
In order for this system to work the crankcase must be sealed. Any leaks will interfere with proper operation, and if they are severe enough the result can be oil blowing back into the air cleaner.
To test the system, pull the breather tube from the rear of the air cleaner and plug a vacuum gauge into it. With the engine running, there should be 3 to 5 inches of vacuum within 15 seconds.
Any openings in the valve cover can allow oil to leak out, and air to leak in. Check for oil around the filler cap (not oil that you've spilled on it while trying to get some in the engine).
Check for oil around the PCV valve and its grommet.
Check for oil at the valve cover hold-down nuts, one at the front and one at the back of the valve cover. There is a grommet on the inside of the valve cover at both of these locations.
The oil filler cap at the front of the valve cover has a rubber gasket on it that should seal it. With age this gasket becomes hard, more like plastic than rubber, and can leak. A new cap is about $3.
With age, all the rubber parts deteriorate, becoming soft, mushy, hard or brittle, and begin to leak.
The two grommets that hold the PCV valve and the intake breather hose are exposed to hot oil from inside the valve cover, causing them to deteriorate over time, becoming soft and mushy and losing their seal. If you see oil around these grommets, they are leaking and should be replaced. The PCV valve and intake breather fitting should fit very tightly into these grommets, sealing solidly.
Other rubber parts are the breather tube and PCV hose, both of which should be inspected and replaced if necessary.
The PCV valve itself should rattle if shaken. If it's gummy and/or sticking, replace it.
There is a small cleaner element in the air cleaner where the PCV air is drawn in. This element must not be clogged shut. If you can't find an exact replacement, get one for any car and simply cut it to size.
A leaking valve cover gasket, which is a well-known problem with the 258, not only makes a mess but can leak PCV vacuum too. My personal preference for fixing this is a cork gasket with plenty of RTV on both sides.
There are two nuts in the center of the valve cover that hold it down, one close to the PCV valve, and the other at the rear almost under the three vacuum solenoids. Under these nuts and inside the cover are two grommets. If these are old and/or cracked they will leak. A new valve cover gasket will come with two new grommets.
If there is always oil around the filler cap, the gasket has lost its resilience. A new cap should fit very snugly and will not leak.
Don't overlook the oil dipstick tube, which should also be sealed.