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The PCV system is designed to prevent blow-by gas from escaping to the atmosphere by drawing it directly into the intake manifold. The PCV valve contains a spring-loaded plunger which is lifted in proportion to intake manifold vacuum. Under high vacuum, blow-by is returned directly to the manifold through the breather chamber and PCV valve with fresh air. When intake manifold vacuum decreases (wide open throttle) and vacuum in the air cleaner increases, the PCV valve closes and the blow-by is returned through the cylinder head cover breather hose and into the air cleaner. The PCV valve also acts as a check valve when the engine backfires to prevent crankcase explosion. Fig. 1: PCV system components-1984-87 1.5L engines Fig. 2: PCV system components-1988-91 1.6L engines Fig. 3: PCV system components-1992-95 engines Fig. 4: PCV system components-1984-87 carbureted engines SERVICE Positive Crankcase Ventilation (PCV) Valve For PCV valve removal, refer to Routine Maintenance of this information. 1. Locate the PCV valve. With the engine running at idle, use pliers to pinch the PCV hose between the valve and the intake manifold. It should be possible to hear the spring loaded valve click shut. 2. If no click is heard, remove the valve from the engine but leave it connected to the intake manifold. A hissing sound should be heard and vacuum should be felt at the valve inlet. 3. If no vacuum is felt, remove the valve from the intake manifold hose. The engine should stall or almost stall. This will indicate a stuck valve or clogged hose. Check the breather hose for clogging or leaks and replace any defective parts. Exhaust Gas Recirculation (EGR) System FUEL INJECTED ENGINES General Information See Figure 3 The Exhaust Gas Recirculation (EGR) system is used to control emissions measured at the tailpipe. Components included are the EGR valve and controls. The EGR system uses a poppet type valve to regulate the amount of exhaust gas flowing into the intake manifold. The flow path is cast into the cylinder head and does not use any external tubing. A control solenoid valve regulates the amount of vacuum to the EGR valve. A Constant Volume Control (CVC) valve provides a constant amount of vacuum to the control solenoid valve over a wide range of engine vacuum. When servicing or repairing any part of the emissions system, it is absolutely essential to check for any obvious mechanical faults or failures. Remember, a trouble code only indicates which sensor or circuit is affected by the problem. Simple mechanical faults such as a vacuum leak or poor electrical connection can cause a fault code. The EGR valve is not simply open or closed but is modulated by controlling the amount of engine vacuum to the valve diaphragm, up to a maximum of 8 in. Hg of vacuum. The EGR valve has a sensor in the top of the valve that reports valve lift to the ECU (same as ECM, 1992-95). The ECU modulates the position of the control solenoid valve to control the EGR valve lift according to an internal program. Upstream of the control solenoid valve, the CVC provides a constant supply of vacuum so EGR control is precise under all manifold vacuum conditions
