99-00 Driver's Side Valve Cover Fix
The PCV valve on 99-00 3.8L V6 Mustangs is located on the driver's side valve cover. At the end of the 2000 model year it was discovered that the 99-00 valve cover has a design flaw that permits engine oil to be drawn up into the PCV valve and then to the upper intake. This oil forms excessive carbon deposits in the combustion chambers that can produce spark knock under heavy acceleration, particularly when running on 87 octane gasoline. This problem is addressed in Ford Service Bulletin No. 8373 and OASIS number 9865. TSB 00-21-8 dated October 2000 describes the same problem occuring on 99-00 Ford Windstar 3.8L V6 engines.
If a customer complains about spark knock, the dealer can take any of several actions, including reprogramming the powertrain control module (PCM) to retard the engine timing, decarbonizing the engine, cleaning the upper intake manifold, and installing a new design drivers' side valve cover. All 2001 and later V6 Mustangs have this new valve cover (Part Number 3F2Z-6582-BA ), which has a modified interior baffle that prevents oil from being sucked into the PCV valve.
Shown above are the 99-00 and 01+ valve covers. As you can see, there are a couple of changes in the design of the interior baffle.
If you've purchased a used 99-00 car, you can tell if it still has its original drivers side valve cover by looking for a sticker on the cover like the one above which indicates the date of manufacture. I have never experienced spark knock on 87 octane gasoline, so I have not yet felt a need to replace the original equipment valve cover on my car. However, I have taken measures to reduce the possibility of spark knock occuring.
In November 2001, I installed an in-line fuel filter between my PCV valve and upper intake to serve as an air/oil separator. When oil vapor hits the surface of the filter it forms into oil droplets that then drain back into the valve cover through the PCV valve. In March 2003, I pulled my upper intake to install a phenolic spacer and had an opportunity to see if this filter was doing any good. The air passages in the upper intake were stained brown from crankcase gases (as would be expected) but they were dry and oil free. When I changed my spark plugs in June 2004, I found no fouling or oil on my plugs. Changed them again in February 2006 and they were still dry and clean. The filter works for me.
Here are photographs of some available filters. The clear glass case allows you to see oil as it collects and drains back into the valve cover through the PCV valve. The filter elements are replaceable. The filter, some 3/8" hose, and two clamps can be purchased from an autoparts store for under $20.
If one of these simple in-line fuel filters doesn't do the trick, you could install a more elaborate oil-air separator such as the one shown below, which costs about $60.
Steeda Autosports P/N 555-3710