The Crankcase Ventilation Valve, also known as the Positive Crankcase Ventilation or PCV Valve, is part of the system used to consume crankcase vapors in the combustion process instead of venting them to atmosphere. Fresh air from the throttle body is supplied to the crankcase, mixed with blow-by gases, and then passed through the crankcase ventilation valve into the intake manifold system. The primary control for this system is the crankcase ventilation valve which meters the flow at a rate depending on inlet vacuum. To maintain idle quality, the valve restricts the flow when inlet vacuum is low (idle or low rpm operation). If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase vent into the throttle body to be consumed by normal combustion.
A plugged valve may cause a rough idle, stalling or slow idle speed, oil leaks and sludge in the engine. A leaking valve would cause a rough idle, stalling and high idle speed. Another area to watch is the rubber grommet which retains most PCV valves. These deteriorate from their constant exposure to engine oil and heat. If the grommet shows signs of cracking or has deteriorated to the point where the PCV valve is not a tight fit, it should be replaced.
The crankcase ventilation valve should be inspected every 30,000 miles (50,000 km) for proper operation. To check, remove the valve, and operate the engine at idle. Place your thumb over the end of the valve to check for vacuum. If there is no vacuum, check for a plugged hose, a clogged manifold port or suspect a failed valve. Turn off the engine and remove the valve and shake it. Listen for the rattle of the check needle inside the valve. If the valve does not rattle, replace it
In general, crankcase ventilation valve service is relatively simple. While the valve can be cleaned in many cases, replacement is recommended.
Description & Operation
The Positive Crankcase Ventilation (PCV) system, also referred to as the Crankcase Ventilation (CV) system, is used on all vehicles to evacuate the crankcase vapors. Fresh air from the air cleaner or intake duct is supplied to the crankcase, mixed with blow-by gases and then passed through a Positive Crankcase Ventilation (PCV) valve into the Air Plenum (upper intake manifold).
When manifold vacuum is high, such as at idle, the orifice or valve restricts the flow of blow-by gases allowed into the manifold. If abnormal operating conditions occur, the system will allow excessive blow-by gases to back flow through the hose into the air cleaner. These blow-by gases will then be mixed with the intake air in the air cleaner instead of in the manifold. The air cleaner has a small filter attached to the inside wall that connects to the breather hose to trap impurities flowing in either direction.
A plugged PCV valve, orifice or hose may cause rough idle, stalling or slow idle speed, oil leaks, oil in the air cleaner or sludge in the engine. A leak could cause rough idle, stalling or high idle speed. The condition of the grommets in the valve cover will also affect system and engine performance.
Diagnosis & Testing
- Check to make sure the engine has the correct PCV valve.
- Start the engine and bring to normal operating temperature.
- Block off PCV system fresh air intake passage.
- Remove the engine oil dipstick and install a vacuum gauge on the dipstick tube.
Run the engine at 1500 rpm for 30 seconds then read the vacuum gauge with the engine at 1500 rpm.
- If vacuum is present, the PCV system is functioning properly.
- If there is no vacuum, the engine may not be sealed and/or is drawing in outside air. Check the grommets and valve cover or oil pan gasket for leaks.
- If the vacuum gauge registers a pressure or the vacuum gauge is pushed out of the dipstick tube, check for the correct PCV valve, a plugged hose or excessive engine blow-by.
- Remove the PCV valve. Please see Section 1.
- With the engine at normal operating temperature, run at idle.
- With the PCV removed from its seat, place a finger over the end to check if vacuum is present. If vacuum is not present, check for plugged hoses or manifold port. Repair or replace as necessary.
- Stop the engine and remove the valve. Shake and listen for the rattle of the check valve needle. If no rattle is heard, replace the valve.
Removal & Installation
3.1L (VIN M) And 3.4L (VIN E) Engines
- Locate the vacuum hoses that run to the fuel pressure regulator and the Positive Crankcase Ventilation (PCV) valve. They should run parallel to each other. It may be necessary to disconnect both hoses, depending on the model and the brackets. The vacuum hose to the ventilation valve terminates on the valve which is pressed into a rubber grommet mounted on one of the valve rocker covers.
- Pull the vacuum hose off of the valve. The valve should be easily pulled from its grommet.
- Install the replacement valve into the grommet. Make sure it is seated properly so there will be no vacuum leaks.
- Connect the vacuum hose(s) to the crankcase valve as well as the fuel pressure regulator, if removed. Verify the hoses are secure.
- Locate the crankcase ventilation valve in its location in its molded rubber connection on the lower side of the intake manifold.
- Remove the valve from its vacuum hose connection.
- Install the replacement valve. Make sure it is seated properly so there will be no vacuum leaks.
- Connect the vacuum hose to the crankcase valve. Test run the engine to verify no vacuum leaks.
- The cosmetic engine cover, also called the fuel injector sight shield, must be removed. Remove this cover by first turning counter-clockwise the tube/oil fill cap from the valve rocker arm cover. Remove the nut holding the shield to the fuel injector rail brace std. Lift the fuel injector sight shield up at the front and slide the tab out of the engine bracket.
- On this engine, the crankcase ventilation valve is under an access cover at the throttle body end of the intake manifold. The cover is under a small pressure from a spring underneath the cover. While holding down the valve access cover, remove the two cover bolts.
- Remove the access cover, then remove the crankcase ventilation valve, the spring and O-ring.
- Install the replacement valve with a new O-ring. Position the spring and install the cover.
- While holding down the ventilation valve access cover, install the cover retaining bolts.
- Install the engine cover by inserting the tab of the cover under the engine bracket. Place the hole of the cover onto the oil fill neck of the rocker arm cover.
- Install the tube/oil fill cap into the rocker arm cover and twist clockwise in order to lock.
- Install the nut holding the cover to the fuel injector rail brace stud and snug down to just 18 inch lbs. (2 Nm).
- The cosmetic/acoustic engine cover is called the fuel injector sight shield. Remove this cover by first turning counter-clockwise the tube/oil fill cap from the valve rocker arm cover. Lift the fuel injector sight shield up at the front and slide the tab out of the engine bracket.
- Locate the Manifold Absolute Pressure (MAP) sensor at the end of the intake manifold. Remove the MAP sensor by disconnecting the electrical connector. Carefully bend the locking tabs holding the MAP sensor to the PCV valve cover just enough to remove the sensor. Pull the MAP sensor straight out of the PCV valve cover.
- Use a 16mm socket to press the access cover down and rotate 1 / 4 turn counter-clockwise. Remove the access cover.
- Remove the PCV valve and the O-ring from the intake manifold.
- Inspect the O-ring. It should be replaced, if necessary. Install the replacement PCV valve. Install the access cover.
- Inspect the seal on the MAP sensor. It should be replaced, if necessary. Position the MAP Sensor to the PCV cover. Make sure the locking tabs engage to hold the MAP sensor to the PCV cover. Plug in the electrical connector.
- Insert the tab of the fuel injector sight shield under the engine bracket. Place the hole of the shield onto the oil fill neck of the valve rocker arm cover. Install the tube/oil fill cap onto the valve rocker arm cover and twist clockwise in order to lock.