The EGR system reduces the oxides of nitrogen (NOx) in the engine exhaust. The reduction of NOx is accomplished by allowing a predetermined amount of the hot exhaust gas to recirculate and dilute the incoming fuel and air mixture. This dilution reduces peak flame temperature during combustion.
See Figure 1
The components of the EGR system on the 2.2L engine are; a Coolant Controlled Exhaust Gas Recirculation/Coolant Vacuum Switch Cold Closed (CVSCC) unit mounted in the thermostat housing, an EGR valve, and a EGR tube.
The CVSCC prevents vacuum from being supplied to the EGR system or other systems until the coolant temperature reaches a certain level. When a certain temperature is reached the CVSCC opens and vacuum is supplied as necessary. To assure proper operation test the system as follows:
- Inspect all passages and moving parts for free movement.
- Inspect all hoses. If any are hardened, cracked or have faulty connections, replacement is necessary.
- Allow the engine to reach normal operating temperature. Locate the EGR valve at the end of the intake manifold. Allow the engine to idle for about a minute, then abruptly accelerate to about 2000 rpm, but not over 3000 rpm. Visible movement of the EGR valve stem should be noticed. Movement of the stem indicates the valve is operating normally. If no movement is noticed. Remove the EGR valve and inspect it for deposits and wear.
- If deposits around the poppet and seat are more than a film, apply some heat control solvent to the area to help soften the deposits. Apply vacuum to the valve with a hand-operated vacuum pump. When the valve opens, scrape away the deposits from the poppet and seat. If the valve poppet does not open when vacuum is applied, replace the valve. If the stem or seat is worn replace the valve.
- If the EGR valve is functioning properly, check the CVSCC.
- Check condition of vacuum hoses at the CVSCC and make certain they are properly routed (see vacuum hose underhood sticker).
- Check engine coolant level.
- Disconnect the vacuum hoses and remove the valve from the thermostat housing. Place the valve in an ice bath below 40°F (4.4°C) so that the threaded portion is covered. Attach a vacuum pump to the lower connection on the valve (the one connected to the vacuum hose showing a yellow stripe). Apply 10 in. Hg (34 kPa) of vacuum. Pressure should drop no more than 1 in. Hg. (6.895 kPa) in one minute. If the vacuum drops more, replace the CVSCC.
See Figure 2
With this system exhaust gases are partially recirculated from an exhaust port in the cylinder head into a port at the intake manifold below the carburetor. EGR flow is controlled by thermo-valves, and a combination of a Dual EGR valve and Sub-EGR valve.
The dual EGR valve consists of a primary and secondary valve, which are controlled by different carburetor vacuum circuits in response to the throttle opening. EGR flow is halted at idle and wide open throttle operation. The primary valve controls the EGR flow at narrow throttle openings, while the secondary valve allows flow into the intake mixture at wider throttle openings. Vacuum to the dual EGR valve is controlled by thermo-valves.
A carburetor mounted Sub-EGR valve is directly opened and closed by the throttle linkage in order to closely modulate the EGR flow controlled by the EGR control valve, in response to the throttle opening.
Two thermo-valves connected to the EGR system, sense coolant temperature changes and open and close accordingly to control the vacuum flow to the EGR system.Test the system as follows:
- Check the vacuum hose for good condition and proper routing (see vacuum hose under hood sticker).
- Engine must be cold. Cold start the engine and allow to idle.
- Check to make sure that the fast idle does not cause the secondary EGR valve to operate. If the secondary EGR valve operates at cold start fast idle, replace the secondary EGR valve thermo-valve.
- Run the engine until the operating temperature exceeds 149°F (65°C). The secondary EGR valve should now be in operation. If if it does not operate, inspect the EGR valve or thermo-valve.
- Disconnect the green stripped vacuum hose from the carburetor. Connect a hand vacuum pump to the hose and apply 6 in. Hg (20 kPa) of vacuum while opening the sub EGR valve by hand. If the idle speed becomes unstable, the secondary valve is operating properly. If the idle speed remains the same, replace the secondary EGR valve and thermo valve.
- Engage the green striped hose to the carburetor. Disconnect the yellow striped hose from the carburetor and connect it to the hand vacuum pump. Hold the sub-EGR valve opened and apply 6 in. Hg (20 kPa) of vacuum.
- If the idle speed becomes unstable, the primary EGR valve is operating properly. If the idle speed remains unchanged, replace the primary EGR valve and thermo valve.
See Figures 3, 4, 5, 6 and 7
The EGR system on these engines, is a back-pressure type. A back-pressure transducer measures the amount of exhaust gas back-pressure on the exhaust side of the EGR valve and varies the strength of the vacuum signal applied to the EGR valve. The transducer uses this back-pressure signal to provide the correct amount of exhaust gas recirculation under all conditions.
This utilizes an intake manifold mounted EGR valve and Electric EGR Transducer (EET). An EGR tube carries the exhaust gases from the intake manifold to the exhaust manifold. The EGR systems are solenoid controlled, using a manifold vacuum signal from the throttle body. The EGR solenoid is part of the EET. These systems do not allow EGR at idle. EGR systems operate at all temperatures above 60°F (16°C).
1989-92 California vehicles, and all 1993-95 vehicles with EGR, have an on-board diagnostic system and a solenoid in series with the vacuum line to the EGR valve. The engine controller monitors EGR system performance and energizes or de-energizes the solenoid based on engine/driving conditions. If the system malfunctions the engine controller will turn on the Check Engine light and a fault code will be stored in the diagnostic system.Test the system as follows:
- Inspect all passages and moving parts for free movement.
- Inspect all hoses. If any are hardened, cracked or have faulty connection, replacement is necessary.
- Warm the engine to normal operating temperature. Allow the engine to idle for about a minute, then abruptly accelerate to about 2000 rpm, but not over 3000 rpm. Visible movement of the groove on EGR valve stem should be noticed. Movement of the stem indicates the valve is operating normally. If no movement is noticed.
- Disconnect the vacuum hoses from the EGR vacuum transducer, and attach a hand-operated vacuum pump. Raise the engine to 2000 rpm and apply 10 in. Hg (34 kPa) of vacuum, while checking valve movement. If no valve movement occurs, replace the valve/transducer assembly.
If the back-pressure EGR valve does not function satisfactory. Replace the entire Valve/Transducer assembly. No attempt should be made to clean the valve.
- If movement occurs, check the diaphragm for leaks. Valve should remain open at least 30 seconds.
- If the valve is functioning satisfactory, remove the throttle body and inspect port in throttle bore and associated passages. Apply some heat control solvent to the area to help soften any deposit.
- Install the throttle body and recheck EGR operation.