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GM 2.4L ECOTEC Positive Crankcase Ventilation (PCV) System

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GM 2.4L ECOTEC Positive Crankcase Ventilation (PCV) System GM 2.4L ECOTEC Positive Crankcase Ventilation (PCV) System Models: GM Terrain, Chevrolet Equinox 2010-2017 28 December 2019 This system utilizes a fixed orifice vacuum port in the intake manifold, baffled ventilation in the camshaft cover and air/oil separator and reservoir in the air intake plenum. There is no PCV valve that regulates air flow under varying intake manifold, instead it uses a fixed orifice at idle and deceleration, and the baffled ventilation and reverse air flow when the engine is under load and throttle body is open. This is a closed PCV system and all air flow is metered through the Mass Air Flow (MAF) sensor or other measured sources. The fixed orifice provides predictable air flow and pressure differential for use by the Engine Control Module (ECM) to accurately regulate fuel control at idle and deceleration, especially in the more commonly used fuel cutoff, lean burn conditions. The small orifice also serves to limit oil vapor and droplets from being drawn into the intake manifold. This is especially important for GDI engines prone to intake valve carbon build-up. The air/oil separator and reservoir utilizes dual stage baffles in the camshaft cover and reservoir in the air intake plenum to reduce oil loss. A fixed PCV tube is utilized to draw air from the camshaft cover and provide ventilation in both directions. Design and Operation of the PCV System As with most PCV systems, the Ecotec PCV system uses intake manifold vacuum and intake plenum air flow to evacuate the crankcase. Measured Intake Manifold is highest at idle at full operating temperature for a mechanically sound engine. Typical readings are 20-22 inHg at idle. 15-16 inHg is typical at cold start-up. At low engine speeds and low load, vacuum will range between 5-15 inHg, and as high as 23-24 inHg under hard deceleration. Under these high vacuum conditions, crankcase vapors are drawn through the fixed orifice and individual orifices in each intake runner. When the engine is under load, intake vacuum can range from very low vacuum to atmosphere pressure to 5 inHg. This is not an issue because the air intake plenum pulls air from the crankcase through the air/oil separator and reservoir. Wide Open Throttle provides the highest crankcase vacuum based on my testing. Testing on a mechanically sound engine and clear PCV system, vacuum is present in the crankcase the vast majority of time, and on average under all driving conditions 100% of the time. It will not be full manifold vacuum, rather .1 to .3 inHg. This is due to the open ventilation through the camshaft cover and air plenum. More importantly in this case is air flow. During cold start up the engine crankcase will see some brief, positive, pressure events and also during highway cruising in overdrive on hills also shows some positive pressure events. None of these events pose a threat to the engine seals. Shifting to a lower gear will maintain vacuum in the engine. We will begin at the intake manifold for the PCV airflow. Image by Jasper Engines showing an orifice in the intake runner which feeds the primary orifice. Image by Jasper Engines showing locations of all four intake runner orifices. They recommend checking air flow through all four in addition to cleaning the PCV orifice. If obstructions are found the manifold should be replaced per Jasper Engines. As of this date I have not found information from GM about these additional pathways. It would make sense to draw vacuum from all four runners. GM may have changed the design and provided a more direct path to the open intake manifold. Image by GM Corporation showing the PCV orifice in the intake manifold and using a drill bit to remove carbon. The purpose of the "D" shaped opening below the orifice is unknown, possibly a fluid trap. More information is needed. Using a fixed orifice size, and measuring manifold pressure or vacuum, precise air flow can be determined by the ECM. GM uses this fact to control air fuel ratios at idle, decel and low load conditions, and for default fuel mapping. The fixed orifice also limits the amount of oil vapor and droplets from entering the engine. Image by Engine Builder Magazine showing the mating surface of the intake manifold and locations of the injectors and intake ports. Located between intake ports 2 and 3 is the opening in the head casting that feeds the orifice. Air flow is drawn down the opening to a low point in the cylinder head and then back up to the orifice located on the intake manifold. Image by sydnesb, Equinox Forums.com showing the top of his cylinder head with the camshaft cover removed. Located in and around the exhaust camshaft valve springs (top of picture) are openings that serve as oil drains leading through the block and to the oil sump. The engine tilts to the rear and this allows for draining of oil shed by the camshafts and lifters during operation. To the right of the Intake camshaft journal #5 is another oil drain. This is much larger and located just below the oil fill cap. The majority of oil collects in this area and drains down to the sump. Some portion of oil collects on the top side of the metal shield and will drain into the top of the head. The three open castings (lower part of the image) allow for air flow from the lower crankcase and to the intake orifice. The center opening feeds the intake orifice only. Image by sydnesb, Equinox Forum.net showing a close-up of the open casting feeding the intake orifice. Inspection of this opening indicated only a small amount of oil. No emulsified oil or carbon build-up. There is a baffle located directly above this opening and is part of the camshaft cover. If a restriction of the orifice is suspected, the camshaft cover can be removed, and a cleaner can be poured into the opening to help reduce the carbon build-up. Compressed air and a towel can be inserted to aid in removal of the carbon. A complete blockage may require removal of the intake manifold. Image by sydnesb, Equinox Forum.net showing the underside of the camshaft cover. Note the darkened areas showing a thin build-up of varnish and deposits. This is from an engine with 100k miles. This darkened area is located nearest the oil fill cap. The images from Steelmesh at KappaPerformance also shows the same deposits. There are three openings in shield that allow air to pass to and from the camshaft area, and for oil to drain when being filled. The open casting on the bottom edge of the cover does not appear to serve a purpose as it is closed off, both in the cover and the head. Image by Steelmesh, KappaPerformance.com showing the baffles and underside of the metal shielding. This is for a non GDI engine, but the baffles and design is the same. Note the color difference and divider between the fresh air side of the camshaft cover and the side drawing crankcase vapors and feeding the middle casting for the intake orifice. There also appears to be much more deposits and a contributing factor is the oil fill cap area. As noted before some oil will likely collect on the top side of the metal shield when oil is filled quickly. The two baffles on the left are single units, whereas the far right leading to the fresh air port is a dual stage baffle. The lighter color and much less deposits is due to the fact that air passes in both directions depending on engine operation, idle verses higher engine loads, and the barrier restricting oil from leaking into that area. The left baffle pulls vapors from the lower crankcase and exits into the camshaft cover or onto the center baffle. The center baffle pulls air from the camshaft cover and low crankcase, traps condensation and droplets and then feeds air to the intake orifice. Crankcase vapors must pass three baffles before it reaches the orifice. This explains the lack of emulsified oil and contaminants in the orifice area. Image by Steelmesh, KappaPerformance.com showing a close-up of the dual stage baffle for the fresh air side of the PCV system. The light colored deposits are similar to the deposits I have found inside the air/oil separator that is part of the air intake plenum. This is likely caused by the small amount of oil vapor that passes and moisture, creating the emulsified oil mixture that is seen in the reservoir and tube. During periods of higher engine load and opening of the throttle body, air is drawn from the camshaft cover and the lower crankcase casting just to the left, through the dual stage baffle to the air intake plenum via the camshaft cover port. Image by Steelmesh, KappaPerformance.com of a close-up of the "dirty side" of the PCV system. The darker deposits is likely caused by direct contact with oil from the oil fill cap and higher temperatures seen from the crankcase. Air flow is in one direction, rising up from the crankcase or from the camshaft cover area and feeding down through the second baffle to the intake orifice. The baffles apprear to limit the amount of oil vapor that reaches the orifice, but over time carbon can build-up as with any PCV system whether a valve or an orifice. Image by Steelmesh, KappaPerformance.com of the camshaft cover, cleaned and ready for modifications and powder coating.
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