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EGR System Honda Prelude III

Testing & Diagnostics 2 illustrations ~1873 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.

CARBURETED

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.

During vehicle deceleration, 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.

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.

EGR CONTROL SOLENOID VALVE

  1. Open the control box lid and disconnect the wire harness from control box. Disconnect lower vacuum hose of EGR control solenoid valve (between the EGR control solenoid valve and the air chamber), from the air chamber. Apply vacuum to the hose. If it does not hold vacuum, go to next step. If it does hold vacuum, replace the EGR control solenoid valve and re-test.
  2. Connect the positive terminal of a 12 volt battery to the Black/Yellow terminal of the control box connector and the negative terminal to the Red terminal. Apply vacuum to the hose. If it does not hold vacuum, replace the EGR control solenoid valve and re-test.

EGR VALVE

  1. Start engine. Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR valve.
  2. Apply 6 in. Hg of vacuum 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.

EGR VALVE LIFT SENSOR

  1. Connect System Checker harness between ECU and connector. Turn ignition ON, and measure voltage between connector "C" terminals No. 13 (Yellow/White) and No. 12 (Green/White). If voltage is 4.75-5.25 volts, go to next step. If voltage is not within specification, substitute a known-good ECU and re-check.
  2. Measure voltage between connector "C" terminals No. 8 (Red/Blue) and No. 12 (Green/White). Voltage should be 1.0-1.4 volts. If voltage is not within specification , go to next step. If voltage is within specification, substitute a known-good ECU and re-test EGR components. See «SYSTEM TESTING»(/honda/prelude/iii-1986-1989/remont/testing-diagnostics/#egr-system) . If EGR still does not operate properly, replace the original ECU.
  3. Turn ignition switch OFF. Check for open or short circuit in Yellow/White, Yellow and Green/White wires between EGR valve lift sensor and ECU. NOTE: If there is no voltage, or if the voltage is low, check for a shorted wire. If voltage is high, there may an open in the wire or a bad connection. If there is any abnormality, go to next step. If not, the wires are faulty.
  4. Turn ignition switch ON. Remove the #16 vacuum hose from the EGR valve, then connect a vacuum pump to upper hose of EGR valve. While applying vacuum, measure the voltage between connector "C" terminals No. 8 (Red/Blue) and No. 12 (Green/White). If the voltages gradually rises, go to next step. If the voltage does not gradually rise, the EGR valve lift sensor is faulty.
  5. Substitute a known-good ECU and re-test EGR components. See «SYSTEM TESTING»(/honda/prelude/iii-1986-1989/remont/testing-diagnostics/#egr-system) . If EGR now operates properly, replace the original ECU.

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 there is 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. Connect voltmeter positive 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 present, proceed to «HOT ENGINE»(/honda/prelude/iii-1986-1989/remont/testing-diagnostics/#egr-system) test. If vacuum is available, check for voltage at EGR control solenoid valve A (Yellow/White wire at emission control box connector).
  3. If voltage is present, 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 there is no voltage, check wiring. Check Brown/Black wire for continuity between control unit and ground. There should be continuity.

Testing EGR Control Solenoid Valve. Scheme 11

Scheme 11: Testing EGR Control Solenoid Valve
Scheme 11: Testing EGR Control Solenoid Valve
  1. Disconnect vacuum hose from EGR valve and connect vacuum gauge to hose. Connect 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 vacuum is present in condition No. 1 or no vacuum available for condition No. 2 and No. 3, check vacuum hose routing. If there are no defects, replace the EGR control valves A and B.
  4. If no voltage is present for condition No. 1 or No. 4, or there is voltage for condition No. 2 or No. 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 there is no voltage, check wiring.
  5. Check Brown/Black wire for continuity between control unit and ground. Wire should have continuity. If vacuum is available for condition No. 4, replace EGR solenoid valve A. Retest system.
  1. Start the engine and warm it up until the cooling fan comes on. Open the control box lid and disconnect No. 16 vacuum hose from the top of EGR valve, connect a vacuum pump to the hose. Pinch the lower hose of the EGR control solenoid valve in the control box, and measure vacuum at idle. If vacuum stabilizes at 6-10 in.Hg (150-250 mmHg) within one second, the CVC valve and EGR hose routing is OK. If vacuum is not 6-10 in.Hg (150-250 mmHg) within one second, check the hose between the intake manifold and CVC valve for clogging or leakage. If the hose is OK, replace the CVC valve.
  2. Unclamp the lower hose pinched in step 1; again measure the amount of vacuum on the vacuum gauge. If vacuum is below 1.2 in.Hg (30 mmHg), the EGR control solenoid valve and hoses are OK. If the amount of vacuum exceeds 1.2 in.Hg (30 mmHg), check the air flow hose to the EGR control solenoid valve, and the No. 17 vacuum hose for blockage. If the hoses are not collapsed or blocked, replace the EGR control solenoid valve and recheck.
  3. Stop the engine. Reconnect the No. 16 vacuum hose, then disconnect the No. 21 vacuum hose from the throttle body. Plug the vacuum tap at the throttle body, connect a vacuum pump to the No. 21 vacuum hose, and apply a vacuum of 12 in.Hg (300 mmHg).
  4. Raise engine speed to 2000-2500 rpm. Feel operation of the EGR control solenoid valve with your fingers. If the EGR control solenoid valve is operating, the system is OK. If the EGR control solenoid valve is not operating, check the EGR control solenoid valve. See «EGR CONTROL SOLENOID VALVE»(/honda/prelude/iii-1986-1989/remont/testing-diagnostics/#egr-system__egr-control-solenoid-valve) . If the solenoid valve is OK, check Black/Yellow wire between the solenoid valve and Regulator fuse (10A), and Yellow wire between the solenoid valve and ECU. If wires are OK, check ECU. If EGR control solenoid valve is normal, check the EGR valve and lift sensor. See «EGR VALVE»(/honda/prelude/iii-1986-1989/remont/testing-diagnostics/#egr-system__egr-valve) & «EGR VALVE LIFT SENSOR»(/honda/prelude/iii-1986-1989/remont/testing-diagnostics/#egr-system__egr-valve-lift-sensor) .

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