there is no check valve only a diaphragm pump on the side of the engine. if this is what you are talking about it is a diaphragm sandwiched between two aluminum blocks and then a gasket between that and the engine.
how to change a valve cover gasket on a 97 mercury grand marquis ?
The PCV valve is located on the back side valve cover. It should be a plug in type and easy to change.
check your idle air control valve
Valve springs
The 2000 Mercury is right at the model change for PCV valves. Some had the valves in a hose under the throttle body. The newer style has no PCV valve at all.
ask a car dealer
You'll need to install a tee into the line by the fuel filter to check it, there is no shrader valve.
Vacuum check valves are usually located close to the vacuum source.
Remove the bolts around the valve covers then the hoses. If your not familiar with working on cars you can take a picture of it before you start removing parts that way you will now where everything goes . Also check out youtube
To change the EGR valve on a 2004 Mercury Mountaineer, first, disconnect the negative battery cable. Remove any components obstructing access to the EGR valve, such as the intake manifold or air cleaner assembly. Unplug the electrical connector and remove the mounting bolts for the EGR valve. Finally, replace the old valve with the new one, reassemble the components, and reconnect the battery.
On a 2000 Merc. it's usually an emissions problem. You can try a water dryer for the fuel and change the PCV valve. If the light remains on, then more than likely it's the EGR valve. Have it tested for free at autozone or Advance auto.
To prevent backflow of mercury, a check valve can be installed in the pipeline. This valve allows fluid to flow in one direction only. Additionally, proper design and maintenance of the system can prevent backflow by ensuring that there are no leaks or breaks in the pipeline.