See Figures 1, 2, 3, 4, 5 and 6
The EGR system is used to reduce oxides of nitrogen (NOx) emission levels caused by high combustion chamber temperatures. This is accomplished by the use of an EGR valve which opens, under specific engine operating conditions, to admit a small amount of exhaust gas into the intake manifold, below the throttle plate. The exhaust gas mixes with the incoming air charge and displaces a portion of the oxygen in the air/fuel mixture entering the combustion chamber. The exhaust gas does not support combustion of the air/fuel mixture but it takes up volume, the net effect of which is to lower the temperature of the combustion process. This lower temperature also helps control detonation.
The EGR valve is mounted on the intake manifold and has an opening into the exhaust manifold. The EGR valve is opened by ported vacuum and allows exhaust gases to flow into the intake manifold. If too much exhaust gas enters, combustion will not occur. Because of this, very little exhaust gas is allowed to pass through the valve. The EGR system will be activated once the engine reaches normal operating temperature and the EGR valve will open when engine operating conditions are above idle speed and below Wide Open Throttle (WOT). On California vehicles equipped with a Vehicle Speed Sensor (VSS), the EGR valve opens when the VSS signal is greater than 2 mph. The EGR system is deactivated on vehicles equipped with a Transmission Converter Clutch (TCC) when the TCC is engaged.
Too much EGR flow at idle, cruise, or during cold operation may result in the engine stalling after cold start, the engine stalling at idle after deceleration, vehicle surge during cruise and rough idle. If the EGR valve is always open, the vehicle may not idle. Too little or no EGR flow allows combustion temperatures to get too high which could result in spark knock (detonation), engine overheating and/or emission test failure.
There are 5 types of EGR valves used; The negative backpressure EGR valve, positive backpressure EGR valve, Ported EGR valve, Integrated Electronic EGR valve and the Digital EGR valve. The principle of all systems is the same; the only difference is in the method used to control how far the EGR valve opens.Negative Backpressure EGR Valve
The negative backpressure EGR valve, used on the 2.0L (VIN P and K) and 2.2L engines, varies the amount of exhaust gas flow into the intake manifold depending on manifold vacuum and variations in exhaust backpressure. Like the ported EGR valve, the negative backpressure EGR valve uses a ported vacuum source. An air bleed valve, located inside the EGR valve assembly acts as a vacuum regulator. The bleed valve controls the amount of vacuum in the vacuum chamber by bleeding vacuum to outside air during the open phase of the cycle. The diaphragm on the valve has an internal air bleed hole which is held closed by a small spring when there is no exhaust backpressure. Engine vacuum opens the EGR valve against the pressure of a spring. When manifold vacuum combines with negative exhaust backpressure, the vacuum bleed hole opens and the EGR valve closes. This valve will open if vacuum is applied with the engine not running.
The positive backpressure EGR valve is used on the 1.8L and 2.0L (VIN H) engines. A vacuum bleed valve, located in the EGR valve, acts as a vacuum regulator, controlling vacuum above the EGR valve diaphragm. Exhaust backpressure is passed through the hollow pintle shaft and exerted on the bleed valve. When sufficient backpressure is applied on the bleed valve, the valve will open, allowing vacuum above the diaphragm to vent to the atmosphere. This will result in the EGR valve closing.
The ported EGR valve, used on the 2.0L (VIN M), takes its name from the fact that it uses a ported vacuum source to open the EGR valve and modulate the EGR flow. The ported vacuum source is a small opening just above the throttle blade in the throttle body. When the throttle begins to open the air passing through the venturi, creates a low pressure which draws on the EGR valve diaphragm causing it to open. As the throttle blade opens further, the ported vacuum increases and opens the valve further.
The ECM controls EGR operation through an EGR control solenoid. Ported vacuum must flow through the EGR control solenoid to open the EGR valve. The ECM uses information received from the Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS) and the Mass Air Flow (MAF) sensor to determine when to allow EGR operation. When certain parameters are met, such as engine at normal operating temperature and the engine speed is above idle, the ECM signals the solenoid to open, allowing EGR operation.
The integrated electronic EGR valve, used on the 2.8L engines, functions like a ported EGR valve with a remote vacuum regulator, except the regulator and a pintle position sensor are sealed in the back plastic cover. The regulator and position sensor are not serviceable. There is a serviceable filter that provides clean fresh air to the regulator along side the vacuum tube.
This valve has a vacuum regulator to which the ECM provides variable current. This variable current produces the desired EGR flow using inputs from the Manifold Absolute Pressure (MAP) sensor, Engine Coolant Temperature (ECT) sensor and engine RPM.Digital EGR Valve
The digital EGR valve, used on the 3.1L engine, is designed to accurately supply EGR to an engine, independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through three orifices which increment in size to produce seven combinations. When a solenoid is energized, the armature, with attached shaft and swivel pintle is lifted, opening the orifice. The flow accuracy is dependent on metering orifice size only, which results in improved control.
The swivel pintle feature insures good sealing of exhaust gas, reducing the need of critical assembly alignment. In addition, the effects of EGR leakage on idle quality are reduced because the shaft and seals are exposed to exhaust pressure instead of manifold vacuum. The shafts are sealed from the exhaust chamber by floating seals held in place by the seal spring. These springs also hold the upper seals that seal the armature cavity in the solenoids. The solenoid coils are fastened together to maximize reliability and to seal the coils from the environment. The coils use a common power terminal with individual ground terminals.
The digital EGR valve is opened by the PCM quad-driver, grounding each respective solenoid circuit. This quad-driver activates the solenoid, raises the pintle, and allows exhaust gas flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will not occur. For this reason, very little exhaust gas is allowed to pass through the valve, with virtually none at idle.
See Figures 7, 8, 9, 10, 11, 12 and 13
Refer to the appropriate chart the test the EGR system.
REMOVAL & INSTALLATION
See Figures 14, 15, 16, 17, 18 and 19
- Disconnect the negative battery cable.
- Remove the air cleaner assembly, as necessary, for access to the EGR valve.
- Disconnect the EGR vacuum hose or solenoid wire, as required.
- Unfasten the EGR valve retaining bolts and remove the EGR valve from the manifold. Remove and discard the EGR valve gasket.
- If reinstalling the old valve, inspect the EGR valve passages for excessive build-up of deposits, and clean as necessary.
Loose particles should be completely removed to prevent them from being ingested into the engine.
- With a suitable scraper or wire wheel buff the deposits from the mounting surfaces.
- Install the EGR valve to the intake manifold using a NEW gasket and tighten the bolts EVENLY.
- Attach the vacuum hose or solenoid wire connector.
- Install the air cleaner assembly, if removed.
- Connect the negative battery cable.
See Figure 20
- Disconnect the negative battery cable.
- Detach the electrical connector at the solenoid.
- Tag and disconnect the vacuum hose(s).
- Unfasten the retaining nut(s), then remove the solenoid.
- Position the solenoid, then secure with the retaining nuts. Tighten the nut(s) to 17 ft. lbs. (24 Nm).
- Connect the vacuum hoses, as tagged during removal.
- Attach the solenoid electrical connector.
- Connect the negative battery cable.