Honda Civic/CRX/del Sol 1984-1995 Repair Guide

Exhaust Gas Recirculation (EGR) System



General Information

See Figures 1 and 2

The EGR system is designed to reduce oxides of nitrogen emission, by recirculating exhaust gas through the EGR valve and the intake manifold into the combustion chambers.

The EGR valve is operated by vacuum from the carburetor port and provides EGR volume proportional to engine loads (intake air volume) by the operation of the EGR control valves A and B.

The EGR system recirculates exhaust gas only after the engine is up to normal operating temperature and then only while accelerating or cruising: these two conditions create the majority of NOx emissions. EGR flow is cut off during idle, deceleration and cold engine operation to assure good combustion during these conditions:

The vacuum signal is ported above the idle throttle valve position to eliminate EGR at idle.
The EGR control solenoid valve A is designed to cut off the EGR flow. When EGR control solenoid valve A is off and ported vacuum is introduced into the EGR valve and EGR control valve A, the EGR valve is opened, allowing exhaust into the intake.
With a cold engine, when the thermosensor B is on, EGR control solenoid valve A is energized and the EGR valve is closed.
When the intake manifold vacuum rises during deceleration, the control switch is turned on to activate EGR control solenoid valve A and the EGR valve flow is cut off.

On 1.5L engine equipped vehicles (1984-87) with automatic transaxle and on all Wagons (1984-87), the EGR control solenoid valve C is designed to control the EGR flow volume according to the driving conditions. When the EGR control solenoid valve C is activated by the control unit venturi vacuum is cut off, the ported vacuum is diluted with air and the EGR flow volume is decreased.

On 1.3L engine equipped vehicles (1984-87), EGR control solenoid valve B is designed to control the EGR flow volume according to the vehicle speed and engine load. When EGR control valve B is activated by the speed sensor and vacuum switch B, the air volume flowing into the diaphragm chamber of the EGR control valve increases and the ported vacuum to the EGR valve is increased.

The EGR system is made up of four sub-systems, these are; the mixture control system, air injection system, auxiliary carburetor air supply system and the feedback control system.

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Fig. Fig. 1: EGR system diagram-1984-87 1.3L engines

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Fig. Fig. 2: EGR system diagram-1987-94 1.5L 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. An air chamber in-line between the CVC and control solenoid acts as an expansion chamber to dampen any vacuum pulses. The control solenoid valve, CVC and air chamber are in the control box on the firewall.

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Fig. Fig. 3: Common EGR system components (located in control box)-1992-95 Civic VX shown


See Figures 4 through 9

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Fig. Fig. 4: EGR system components-1988-91 fuel injected engines

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Fig. Fig. 5: EGR system components-1992-95 fuel injected engines

Only one Civic model manufactured after 1992 is equipped with the EGR system: the Civic VX.

  1. First check that all vacuum lines and electrical connections are in good condition. If the engine will not run at idle, disconnect the vacuum hose to the EGR valve and plug it. If the engine will now idle, the problem is in the EGR control system. Run the engine until the radiator fan comes on. Disconnect the vacuum supply hose No. 16 to the EGR valve and connect a hand vacuum pump with a gauge to the valve.
  3. With the engine at idle, draw a vacuum on the EGR valve. The engine should stall and the valve should hold vacuum. If not, replace the EGR valve.
  5. Connect the hand pump with vacuum gauge to the No. 16 vacuum hose from the control solenoid valve and restart the engine; there should be no vacuum at idle.
  7. If there is vacuum to the EGR valve at idle, check the wiring for the control solenoid. One wire should have 12 volts any time the engine is running. The ground wire goes to the ECU, which modulates the control solenoid opening by controlling the ground circuit. Turn the ignition switch OFF and use an ohmmeter to see if the wire between the ECU and control solenoid is shorted to ground. If the wiring is correct, the ECU is getting an incorrect input signal or the ECU is faulty.
  9. The vacuum going to the control solenoid valve should be about 8 in. Hg at idle. Connect the pump with gauge to the hose coming from the air chamber. If the vacuum is not correct, read the vacuum at the CVC valve outlet. Full manifold vacuum should be available at the CVC inlet. If the air chamber or CVC valve leak or are not functioning properly, the units cannot be repaired.

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Fig. Fig. 6: Connect the vacuum pump to the EGR valve by disconnecting vacuum hose No. 16

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Fig. Fig. 7: Checking for engine vacuum by disconnecting vacuum hose No. 12

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Fig. Fig. 8: Connecting the vacuum pump to the CVC valve

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Fig. Fig. 9: Terminal locations for the EGR control connectors

  1. To test the EGR valve lift sensor, turn the ignition OFF and disconnect the wiring to the EGR valve. Turn the ignition switch ON and check for 5 volts to the sensor at one of the connector terminals. Switch the ignition OFF , connect an ohmmeter across the center and either of the end terminals on the EGR valve lift sensor connector and operate the EGR valve with the vacuum pump. The resistance should change as the valve opens and closes.