1991 Mazda MPV PCV Valve Replacement Cost

As the engine operates, small fires inside each engine cylinder create pressure that pushes the engine piston down, toward the crankshaft, and some combustion gases from the fire in the cylinder are able to get around the piston, and enter the crankcase. Also, heat from the engine causes the air inside the crankcase to expand. If this condition were left untreated, the engine would develop leaks, and would suffer severe inefficiency, if it ran at all. To prevent this situation, the crankcase ventilation system connects the crankcase to the intake manifold. The intake manifold is constantly under vacuum as the engine sucks in air, so when the crankcase ventilation valve is installed, the hot gases are sucked from the engine crankcase, and burned in the engine as fuel.

Rough idling, lack of power, engine oil leaks, engine burning oil, and illumination of the check engine light are all possible if the PCV valve has clogged. If the check engine light comes on, the on-board diagnostics (OBD) trouble codes will most likely relate to manifold vacuum, air and fuel mixture, PCV system, mass airflow sensor readings, and exhaust and emissions readings. These are all affected in the event the PCV valve is clogged, is stuck fully open, or is stuck fully closed, however, if the valve is stuck fully open, the engine oil seals are not in danger of overpressure.

Driving with the PCV valve stuck closed or clogged is not recommended. If the vehicle must be driven, keeping the engine speed low is the safest bet, as this will also decrease the amount of pressure in the crankcase. If the PCV valve is stuck open, there is no harm in driving, however, the vehicle may experience poor fuel mileage, vibrations, and the dreaded check engine light as the computer registers this condition as a vacuum leak.

PCV valves are a common repair since they are part of the factory scheduled maintenance plan. PCV valves are recommended from 35,000 -60,000 miles, with most being right at the 50,000 mile mark. Many turbocharged engines require more frequent changes, and may have a secondary PCV valve in the PCV system. PCV valves often fail early, mostly due to a lack of maintenance. If the engine oil turns sludgy, that sludge will build up on the PCV valve, quickly clogging the valve, and necessitating replacement.

Understanding what the PCV valve does make diagnostics a breeze for anyone. If the technician suspects the PCV valve has failed, he will remove the valve, and use his hand-help pump to apply vacuum, then forced air, to see how the PCV reacts. If air can freely move through the valve in the intended direction, it is working properly. The valve has failed the test if air moves through in both direction or neither direction, or if air only moves in the wrong direction.

Replacing the PCV valves can take seconds on some vehicles, and even an hour or two on others. In all cases, replacing the part is easy, but accessibility is not always on the technician's side. Vehicle are purpose-built, and most are built to be economical and reliable. This means placing components that frequently fail in expected positions, and unobstructed from removal. For vehicles that are built for high-luxury, performance, or off-road use, the placement of components is strictly for the purpose of enhancing performance, and may be very complicated to service.

We recommend using the OEM PCV valve if possible. The manufacturer will update parts as needed, and having the latest revision could save time, trouble, and money in the future.

Engines with clogged PCV valves should be examined to discover the purpose of the clogged valve. Under normal conditions, the PCV valve should not clog. If clogging occurs, the engine should undergo a brief scan to inspect the engine running conditions. Lastly, the engine should be checked for engine sludge, as this is the major cause for many issues, including PCV valve clogs, and catching engine sludge early is vital to the longevity of the engine.

In many cases, replacing the PCV valve is a straightforward process. The valve is usually pretty easy to access, depending on what model of car you have. If you can get to the valve without having to remove other parts, it's a simple matter of pulling the old valve out and pushing the new one in.