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EGR System Honda Prelude II

Testing & Diagnostics 1 illustration ~1013 words

DESCRIPTION

Honda uses exhaust gas recirculation (EGR) on all models to reduce oxides of nitrogen (NOx) emissions. The system includes a special intake manifold and cylinder head, EGR valve, EGR control valves, EGR switch and EGR control solenoid valves. Vehicles also use a control unit, thermosensor, control switch solenoid valve and vacuum switch.

OPERATION

The EGR system operates only when the engine is at normal operating temperature and only while accelerating or cruising. The vacuum control signal is carburetor ported vacuum. A thermosensor eliminates EGR when engine coolant is below normal operating temperature.

When vehicle is decelerating, manifold vacuum rises and turns on EGR control switch. The EGR control solenoid valve closes and cuts off EGR flow. Vacuum is provided to EGR control switch only above 15 MPH, when the speed sensor opens the throttle opener solenoid valve.

EGR control valves A and B use a ported vacuum signal to control a manifold vacuum flow large enough to operate the EGR valve. With this system, the EGR valve is operated by a signal proportional to airflow through carburetor venturi, ensuring correct EGR flow.

EGR control valves A and B receive vacuum from vacuum switch C.

EGR VALVE

  1. Start engine. Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR valve.
  2. Apply 6 in. Hg to EGR valve. Ensure vacuum holds steady. Engine should die. If vacuum does not hold, replace EGR valve. If engine does not die, check EGR valve and ports for blockage.

THERMOSENSOR

  1. Thermosensor resistance must be checked both cold and hot. Coolant temperature must be less than 104°F (40°C) to perform cold resistance check. Disconnect vacuum hose No. 19 from charcoal canister. If there is no vacuum at idle, thermovalve B is open and thermosensor resistance check can be performed.
  2. Disconnect connector at control unit. Check for resistance between Blue/Yellow and Brown/Black terminals. Resistance should be above 1000 ohms. Run engine until cooling fan comes on and check resistance again. Resistance should be about 200 ohms.
  3. If resistance is not within specifications, replace thermosensor and retest. If ohmmeter shows no continuity, check wires. If there are no defects, replace thermosensor and retest.

Switch A

Disconnect No. 2 hose from control box at vacuum hose manifold. Connect vacuum pump to hose. Check for continuity between Black/Yellow wire and Brown/White wire terminals of control box connector. There should be no continuity when more than 3.9 in. Hg vacuum is applied to switch. There should be continuity when vacuum is released.

Switch B

Disconnect No. 7 hose from control box at vacuum hose manifold. Connect vacuum pump to hose. Check for continuity between Black/Yellow wire and Gray wire terminals of control box connector. There should be continuity when more than 1.2 in. Hg vacuum is applied to switch. There should be no continuity when vacuum is released.

Switch C

Disconnect No. 15 hose from control box at vacuum hose manifold. Connect vacuum pump to hose. Check for continuity between Black/Yellow wire and Blue/Black wire terminals of control box connector. There should be continuity when more than 1.2 in. Hg vacuum is applied to switch. There should be no continuity when vacuum is released.

CONTROL UNIT CONNECTORS

Check for voltage at control unit connector (Blue and Black/Yellow wires) with ignition on. If no voltage at Black/Yellow wire, check wiring. If there is no voltage at Blue wire, check wire between ignition coil and control unit. Check Brown/Black wire for continuity between control unit and ground. There should be continuity.

SPEED SENSOR

  1. Raise and support front of vehicle. Push the voltmeter probe into Yellow/Black wire terminal at control box No. 1 connector. Connect negative probe to ground. Start engine.
  2. Select second gear (man. trans.) or position "2" (auto. trans.) and accelerate slowly, while observing voltmeter. Voltage should be battery voltage below 11 MPH and no voltage above 16 MPH. If so, sensor is okay. If not, install a new sensor and retest.
  3. If there is no voltage during speed sensor test, check for bad electrical connection, fuse or faulty speed sensor. Repair or replace as necessary and retest.
Fig. 1: EGR System
Scheme 1: EGR System

COLD ENGINE

  1. Disconnect vacuum hose No. 16 from EGR valve and connect vacuum gauge to hose. Start engine and raise engine speed to 4500-5000 RPM. Vacuum should not be available.
  2. If vacuum is not available, proceed to «HOT ENGINE»(/honda/prelude/ii-1983-1987/remont/testing-diagnostics/#egr-system__hot-engine) test. If vacuum is available, check for voltage at EGR control solenoid valve A (Yellow/White wire at emission control box connector).
  3. If there is voltage, replace EGR control solenoid valve A and retest. If there is no voltage, check thermosensor operation, wiring, and fuses and retest. Check thermosensor and vacuum switch C.
  4. Check for voltage at control unit connector (Black/Yellow wire) with ignition on. There should be voltage. If no voltage, check wiring. Check Brown/Black wire for continuity between control unit and ground. There should be continuity.

HOT ENGINE

  1. Disconnect vacuum hose from EGR valve and connect vacuum gauge to hose. Push a voltmeter positive probe into the terminal at the control box connector (Yellow/White wire). Connect the negative probe to ground.
  2. Start and warm-up engine to normal operating temperature (cooling fan must come on). Test EGR system under the following engine operating conditions. Check vacuum and voltage specifications. EGR SYSTEM TEST Engine Condition EGR Valve Vacuum Yellow/White Wire Voltage 1 Idle None Yes 2 Hard Accel. 2-6 in. Hg None 3 4500 RPM 2-6 in. Hg None 4 Deceleration None Yes
  3. If there is vacuum available in condition 1 or no vacuum available for condition 2 and 3, check vacuum hose routing. If there are no defects, replace the EGR control valves A and B.
  4. If there is no voltage for condition 1 or 4, or there is voltage for condition 2 or 3, check thermosensor and vacuum switch C. Check for voltage at control unit connector (Black/Yellow wire) with ignition on. There should be voltage. If no voltage, check wiring.
  5. Check Brown/Black wire for continuity between control unit and ground. Should have continuity. If vacuum is available for condition 4, replace EGR solenoid valve A. Retest system.

See also:
• HOT ENGINE

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