EGR System: Other Honda Civic II

CARBURETED

System is regulated by a dual EGR control valve located in control box. When ported vacuum is directed to control valve A, valve opens and manifold vacuum passes through vacuum chamber of control valve B. Vacuum is then bled off into air filter through a restricted orifice. This causes control valve B, as well as EGR valve to begin to open.

As control valve B opens, ported vacuum is bled off to carburetor venturi area, causing ported signal to control valve A to be reduced. This causes control valve B to close. As control valve B closes, ported signal is increased and process is repeated. Because these steps are repeated very rapidly, carburetor intake air volume and ported signal to EGR valve are proportional to engine load.

When engine is cold, vacuum signal to EGR valve is bled off to air cleaner through thermovalve A (Accord) or to atmosphere through EGR cut-off solenoid (Prelude).

FUEL INJECTED

The EGR lift sensor detects amount of EGR valve lift and sends this information to ECU. ECU compares lift signal with internal calibration tables and modifies signals to EGR control solenoid to produce the desired vacuum signal to the EGR valve. Manifold vacuum signal to solenoid is regulated at about 8 in. Hg by the Constant Vacuum Control (CVC) valve. If lift sensor signal does not respond to regulated vacuum signal as expected, ECU will set code 12 in memory and turn on the dash mounted PGM-FI warning light. If light is on and code 12 is set in memory, see appropriate article in the COMPUTERIZED ENGINE CONTROLS section.

Accord - Carbureted

1. With coolant temperature less than 131° F (55° C), disconnect vacuum hose No. 19 at thermovalve. Using a hand-held vacuum pump, apply vacuum to thermovalve port. Vacuum should not hold. If vacuum holds, disconnect air cleaner bleed hose from thermovalve. If vacuum bleeds off, check for restriction in hose or at air cleaner. If vacuum does not bleed off, replace thermovalve.
2. Start engine. Disconnect air cleaner bleed hose at thermovalve. Disconnect vacuum hose No. 19 at thermovalve. Connect vacuum gauge to No. 19 hose. Increase engine speed to about 3000 RPM. Verify presence of vacuum. If vacuum is not present, check for defective check valve or restricted orifice. Also check for plugged vacuum port at carburetor.
3. Allow engine to idle. Reconnect hose No. 19 to thermovalve. Connect vacuum gauge to air cleaner thermovalve fitting. Increase engine speed to about 3000 RPM. With coolant temperature less than 131°F (55°C), vacuum should show on gauge. Disconnect vacuum gauge.
4. Allow engine to reach operating temperature (cooling fan comes on). Reconnect vacuum gauge at thermovalve bleed fitting. Vacuum should not show on gauge. If thermovalve does not react as specified, replace thermovalve.

EGR CUT-OFF SOLENOID

1. Disconnect vacuum hose at EGR valve. Connect vacuum gauge to hose. Warm engine to operating temperature (cooling fan comes on). Increase engine speed to about 3000 RPM. If vacuum is shown on gauge, solenoid is operating properly.
2. If vacuum is not shown on gauge, disconnect EGR cut-off solenoid connector. Turn ignition on. Connect negative voltmeter lead to ground. Check for voltage at EGR solenoid connector. If voltage is not present, check for blown fuse, or open or short in solenoid power supply wire. (Scheme 19)- (Scheme 23). Also see appropriate wiring diagram in the COMPUTERIZED ENGINE CONTROLS section.
3. If voltage is present, increase engine speed to about 3000 RPM. Check voltage across solenoid terminals. If voltage is shown and vacuum is not present on gauge, check for restricted hose or replace defective solenoid.
4. If voltage is not present, check for open ground wire to solenoid. (Scheme 19)- (Scheme 23). Also see appropriate wiring diagram in the COMPUTERIZED ENGINE CONTROLS section. If ground wire is okay, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.

CONSTANT VACUUM CONTROL (CVC) VALVE

Start engine. Verify presence of manifold vacuum to CVC valve. Disconnect CVC vacuum hose at EGR solenoid. Connect vacuum gauge. If vacuum reading is not about 8 in. Hg, replace CVC valve.

Fuel Injected & Prelude Carbureted

1. Disconnect coolant temperature (TW) sensor connector. Measure resistance across sensor terminals. Resistance should be less than 1000 ohms if coolant temperature is greater than 100°F (38°C).
2. Start engine. Allow engine to reach operating temperature (cooling fan comes on). Measure resistance across sensor terminals. Resistance should be 200-400 ohms. If sensor values are not within specification, replace thermosensor.

Scheme 19

Scheme 20

Scheme 21

Scheme 22

Scheme 23

EGR VALVE FUNCTIONAL

Start engine and allow to idle. Disconnect vacuum hose from EGR valve. Connect hand-held vacuum pump. Apply at least 6 in. Hg. If engine dies and vacuum holds, EGR valve is functioning properly. If engine does not die and vacuum does not hold, replace EGR valve. If engine does not die but vacuum holds steady, remove EGR valve. Check for plugged valve or passages. Clean or replace as necessary. On fuel injected models, if PGM-FI light is illuminated, proceed to appropriate article in the COMPUTERIZED ENGINE CONTROLS section.

1. Ensure coolant temperature is less than 131°F (55°C) on Accord models or less than 145°F (63°C) on Prelude 49-state models. Disconnect vacuum hose from EGR valve and connect vacuum gauge to hose. Start engine and increase engine speed to 3000 RPM. EGR valve should not receive vacuum. If vacuum is not available to EGR valve, proceed to «HOT ENGINE»(ref-94324-S17675407842001033000000) test.
2. If vacuum is present on Accord models, replace thermovalve A and retest. If vacuum is present on Prelude 49-state models, proceed to EGR CUT-OFF SOLENOID test.

1. Disconnect vacuum hose from EGR valve and connect vacuum gauge to hose. Start engine and warm to operating temperature (cooling fan comes on). EGR vacuum should respond as indicated in «EGR VACUUM TEST»(ref-94324-S19321316302001033000000) table. If vacuum is not as indicated in table, remove control box and open lid.
2. If vacuum is present during condition No. 1, check vacuum hose routing and connections. Verify correct idle speed and mixture. Adjust as necessary.
3. If no vacuum is available for conditions No. 2 and No. 4, check for vacuum at inlet thermovalve A (Accord) or cut-off solenoid (Prelude). If vacuum is present on Accord, replace thermovalve. If vacuum is present on Prelude models, proceed to «EGR CUT-OFF SOLENOID»(ref-94324-S00941544832001033000000) test.
4. If vacuum was greater than 2 in. Hg for condition No. 3, replace EGR control valve (A/B). Ensure vacuum hoses are routed properly.

EGR VACUUM TEST