Engine Controls - System/component Tests - Carbureted Honda Prelude III рестайлинг

INTRODUCTION

Before testing separate components or systems, perform procedures in BASIC TESTING - CARBURETED article. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform procedures in TESTS W/CODES - 2.0L PGM-CARBURETED article.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on ECU terminals A24, A26, D19 and D21. (Scheme 1) Resistance should be zero ohms. If resistance is not zero ohms, repair open circuit.
2. Using a DVOM, touch negative voltmeter lead to a good ground. Touch positive voltmeter lead to each ground terminal. With vehicle running, voltmeter should indicate less than.1 volt. If voltmeter reading is greater than.1 volt, check for open, corrosion or loose connection on ground lead.

Scheme 1

1. Using a voltmeter, check for battery voltage between ECU terminal D1 and ground. (Scheme 1) If battery voltage is not present, check EFI/ECU fuse in underhood fuse box. If fuse is okay, check for an open or short in Yellow/Blue wire between fuse box and control unit terminal D1.
2. Turn ignition switch to ON position. DO NOT start engine. Using a voltmeter, check for battery voltage between ECU terminal A25 and ground. (Scheme 1) If battery voltage is not present, check fuse No. 12 in dash fuse box. If fuse is okay, check for a defective ignition switch or an open or short in Black/Yellow wire between fuse box and ECU terminal A25.

ENGINE SENSORS & SWITCHES

Note. ECU Test Harness (07LAJ-PT30100 ) is needed when testing certain components or systems. Test harness must be connected between the ECU and main wire harness connectors. ECU is located under passenger's side floorboard carpet. (Scheme 2)

Scheme 2

SIGNAL TESTING

1. Connect ECU Test Harness (07LAJ-PT30100 ) between ECU and ECU connector. (Scheme 2) Disconnect "D" connector from main wire harness only, not ECU. Turn ignition switch to ON position. DO NOT start engine. Measure voltage between terminal D6 (positive) and terminal A26 (negative). (Scheme 1) If battery voltage is present, go to step 3). If battery voltage is not present, go to next step.
2. Substitute a known good ECU and recheck voltage between terminals D6 and A26. If voltage is now available, replace original ECU.
3. Reconnect "D" connector to main wire harness. Place a jumper wire between terminals A19 and A26. (Scheme 1) If A/C system operates, go to step 4). If A/C system does not operate, connect Red/Blue terminal of 4-pin connector on A/C clutch relay to chassis ground. If A/C system now operates, repair open or short in Red/Blue wire between terminal A19 and compressor control unit. If A/C system still does not operate, A/C system may be faulty.
4. Start engine. Turn blower switch on. Turn A/C switch on. If A/C system does not operate, A/C system may be faulty. If A/C system operates, measure voltage between terminals D6 (positive) and A26 (negative). (Scheme 1) If voltage is below one volt, A/C signal is okay. If voltage is not below one volt, repair open or short in Red/Green wire between ECU terminal D6 and A/C switch.

CONTINUITY TEST

Turn ignition off. Disconnect 2-wire connector from clutch switch. Connect an ohmmeter across clutch switch terminals. Depress and release clutch pedal. If continuity does not change from zero to infinity, adjust or replace clutch switch.

RESISTANCE TEST

Disconnect 2-wire connector from coolant temperature sensor and measure resistance between 2 sensor terminals. Resistance should be as specified in COOLANT TEMPERATURE (TW) SENSOR RESISTANCE table. Replace sensor if resistance is not as specified.

COOLANT TEMPERATURE (TW) SENSOR RESISTANCE (1)

Disconnect 2-wire connector from TA sensor. Measure resistance between TA sensor terminals. Resistance should be as specified in INTAKE AIR TEMPERATURE (TA) SENSOR RESISTANCE table. Replace TA sensor if resistance is not as specified.

INTAKE AIR TEMPERATURE (TA) SENSOR RESISTANCE (1)

VOLTAGE TEST

Disconnect vacuum hose from Manifold Absolute Pressure (MAP) sensor and connect a hand-held vacuum pump. Apply specified vacuum to MAP sensor and measure voltage between ECU terminals D17 (positive) and D22 (negative). (Scheme 1) See MAP SENSOR VOLTAGE table. Voltage reading should be as specified. Replace MAP sensor if vacuum does not hold or voltage is not within specified.

MAP SENSOR VOLTAGE

1. Warm engine to normal operating temperature (cooling fan comes on). Disconnect wiring harness from O2 sensor connector. While measuring voltage between sensor connector and ground, rapidly accelerate engine to 5000 RPM and quickly release throttle.
2. Voltage reading should be greater than 0.6 volt at high RPM and less than 0.4 volt when throttle is quickly released. If voltage is not within specification, replace O2 sensor. If voltage is okay, go to next step.
3. Turn ignition off and reconnect O2 sensor connector. Connect ECU Test Harness (07LAJ-PT30100 ) between main wire harness and ECU. (Scheme 2) Start engine and warm to normal operating temperature again. Measure voltage between terminals D13 (positive) and D21 (negative), while rapidly accelerating engine to 5000 RPM and quickly releasing throttle. (Scheme 1)
4. Voltage reading should be greater than 0.6 volt at high RPM and less than 0.4 volt when throttle is quickly released. If voltage is not as specified, check for an open or short in White wire between O2 sensor and ECU.

Scheme 3

Scheme 4

1. Turn ignition off. Disconnect 8-pin connector on vacuum switch control box. (Scheme 3) Measure resistance between terminals No. 5 and No. 6 on control box connector. If continuity exists, go to step 3). If continuity does not exist, remove hose No. 7 from vacuum hose manifold. (Scheme 4) Connect a "T" fitting from a vacuum gauge between vacuum hose manifold and vacuum switch.
2. Start engine and idle. Check vacuum gauge. If vacuum is greater than 1.2 in. Hg, check routing of hose No. 7. If vacuum is less than 1.2 in. Hg, replace vacuum switch and/or repair open or short in Black/Yellow or White wire in control box.
3. Turn ignition switch to ON position. Measure voltage between Black/Yellow terminal and body ground on wire harness. If battery voltage does not exist, repair open or short in Black/Yellow wire between 8-pin connector and No. 12 fuse. If battery voltage is present, vacuum switch is okay.

1. Turn ignition off. Connect ECU Test Harness (07LAJ-PT30100 ) between main wire harness and control unit. (Scheme 2) Block rear wheels and set parking brake. Raise front of vehicle and support with safety stands.
2. Turn ignition switch to ON position. On vehicles with A/T, place transmission in Neutral. Slowly rotate left front wheel and measure voltage between ECU terminals D9 (positive) and D21 (negative). (Scheme 1) If voltage pulses from 0 to 5 volts, vehicle speed pulser is okay. If voltage does not pulse as described, go to next step.
3. Turn ignition off and disconnect ECU test harness from ECU only. Turn ignition switch to ON position. Slowly rotate left front wheel and measure voltage between terminals D9 (positive) and A25 (negative). (Scheme 1)
4. If voltage pulses from 0 and 12 volts, replace ECU and retest. If voltage does not pulse between 0 and 12 volts, check for an open or short in White/Blue wire between ECU terminal D9 and speed pulser. If no open or short is found, replace speed pulser.

FUEL CUT-OFF RELAY

The solid-state fuel cut-off relay does not have a given resistance or test value. Before replacing relay, perform the following procedure to eliminate possible wiring harness and input signal problems.

Scheme 5

Scheme 6

1. With ignition switch off, remove driver's side dash undercover and pull down fuse box/relay panel. Remove fuel cut-off relay. (Scheme 5) Using relay socket cavity terminals, check for continuity between No. 3 terminal and ground. If continuity does not exist, check for an open or short in Black wire between relay and ground.
2. Attach positive voltmeter lead to No. 2 terminal and negative lead to No. 3 terminal. Turn ignition switch to ON position. If battery voltage is not present, check Black/Yellow wire from ignition switch to fuel cut-off relay for open or short. Check No. 12 fuse. Repair or replace as necessary.
3. Turn ignition off. Attach positive probe of voltmeter to No. 4 terminal and negative probe to No. 3 terminal. Turn ignition switch to ON position. If battery voltage is not present, check Blue wire between ignition coil and fuel cut-off relay for open or short.
4. Turn ignition off. Connect a jumper wire between terminals No. 1 and No. 2. (Scheme 5) Turn ignition switch to ON position. Fuel pump should run. If in-tank fuel pump does not run, remove left maintenance access cover in luggage compartment area and disconnect 2-pin fuel pump connector. (Scheme 6)
5. Connect positive voltmeter lead to Yellow/Black terminal of fuel pump connector and negative voltmeter lead to ground. (Scheme 6) If battery voltage is not present, check Yellow/Black wire between fuel cut-off relay and fuel pump for open or short. If battery voltage is available, check Black wire between fuel pump connector and ground. If Black wire is okay, replace fuel pump.

A/C IDLE BOOST SOLENOID VALVE

See IDLE SPEED .

AIR LEAK SOLENOID VALVE

See FUEL CONTROL .

AIR SUCTION CONTROL SOLENOID VALVE

See EMISSION SYSTEMS & SUB-SYSTEMS .

AIR VENT CUT-OFF SOLENOID VALVE

See EMISSION SYSTEMS & SUB-SYSTEMS .

CRANKING LEAK SOLENOID VALVE

See IDLE SPEED .

INNER VENT SOLENOID VALVE

See EMISSION SYSTEMS & SUB-SYSTEMS .

POWER VALVE CONTROL SOLENOID VALVE

See FUEL CONTROL .

PRIMARY SLOW MIXTURE CUT-OFF SOLENOID VALVE

See FUEL CONTROL .

PURGE CUT-OFF SOLENOID VALVE

See EMISSION SYSTEMS & SUB-SYSTEMS .

VACUUM PISTON CONTROL SOLENOID VALVE

See FUEL CONTROL .

Scheme 7

1. Remove air cleaner cover and air filter. Disconnect vacuum hose to air leak solenoid valve and connect a vacuum pump to hose. (Scheme 7)
2. With intake air temperature less than 145°F (63°C), start engine and warm to operating temperature (cooling fan comes on). Apply 4 in. Hg with hand-held vacuum pump. If air leak solenoid valve does not hold vacuum, go to step 4). If vacuum is held, go to next step.
3. If intake air temperature is less than 145°F (63°C), warm air bleed valve "B", located in air cleaner chamber, with a hot air gun. If solenoid valve holds vacuum now, replace air bleed valve "B". If vacuum is not held, remove top hose from air leak solenoid valve and plug solenoid valve. If intake air temperature is less than 158°F (70°C), warm TA sensor with a hot air gun. If solenoid valve now holds vacuum, go to step 5). If vacuum is not held, air leak solenoid valve is okay.
4. Turn ignition off. Disconnect Green connector near air cleaner. Start engine and measure voltage between Green (positive) wire terminal and ground. If battery voltage is present, replace solenoid valve. If battery voltage is not present, check CHECK ENGINE light and self-diagnosis LED indicator. If okay, repair open or short in Green wire between solenoid valve and control unit terminal A12.
5. Turn ignition off. Disconnect Green connector near air cleaner. Start engine and measure voltage between Green (positive) wire terminal and ground. If voltage is not present, replace solenoid valve. If voltage is present, check CHECK ENGINE light and self-diagnosis LED indicator. If okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.

Scheme 8

1. Disconnect solenoid valve No. 14 vacuum hose from vacuum hose manifold and connect a hand-held vacuum gauge. (Scheme 8) Start engine. If vacuum is present, turn ignition off and go to next step. If vacuum is not present, go to step 4).
2. Disconnect 4-pin connector near solenoid valve. Start engine. Measure voltage between Green/Yellow (positive) terminal and Black (negative) terminal on wire harness. (Scheme 8) If battery voltage is present, replace solenoid valve. If battery voltage is not present, measure voltage between Green/Yellow (positive) terminal and body ground.
3. If battery voltage is present, repair open or short in Black wire between solenoid valve and ground. If battery voltage is not present, check CHECK ENGINE light and self-diagnosis indicator. If okay, check for open or short in Green/Yellow wire between control box and control unit.
4. Warm engine to normal operating temperature (cooling fan comes on). Check vacuum gauge. If vacuum is present, solenoid valve is okay. If vacuum is not present, turn ignition off. Disconnect 4-pin connector near solenoid valve. (Scheme 8)Start engine. Measure voltage between Green/Yellow (positive) terminal and Black (negative) terminal on wire harness.
5. If battery voltage is present, replace solenoid valve. If battery voltage is not present, check CHECK ENGINE light and self-diagnosis LED indicator. If voltage is present, substitute a known good control unit and retest. If symptom goes away, replace original control unit.

Scheme 9

1. Turn ignition switch to ON position and check for a clicking sound at each solenoid valve. (Scheme 9) If solenoid valves do not click, go to step 4). If each solenoid valve clicks, go to next step.
2. Start engine and warm to normal operating temperature (cooling fan comes on). Raise and support front of vehicle. Block rear wheels and set parking brake. Place transmission in 2nd gear or in "2" position, accelerate to 4000 RPM and then suddenly release throttle. Check for clicking sound at each solenoid valve while decelerating from greater than 12 MPH and 4000 RPM. If solenoid valves clicks, valve is okay. If solenoid valves do not click, go to next step.
3. Turn ignition off and connect ECU Test Harness (07LAJ-PT30100 ) between ECU and main harness connector. (Scheme 2) Start engine and measure voltage between terminals A21 (positive) and A26 (negative) (Scheme 1)during deceleration from greater than 12 MPH and 4000 RPM. If voltage momentarily ceases during deceleration, replace solenoid valve. If voltage does not cease, observe CHECK ENGINE light and self-diagnosis LED indicator. If okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.
4. If solenoid valve did not click, turn ignition off. Connect ECU Test Harness between ECU and main connector. (Scheme 2) Turn ignition switch to ON position and measure voltage between ECU terminals A21 (positive) and A26 (negative). (Scheme 1) If battery voltage is present, go to step 5). If battery voltage is not present, observe CHECK ENGINE light and self-diagnosis LED indicator. If okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.
5. If battery voltage was present, check for open or short in Black/Yellow wire between solenoid valve and ECU terminal A21. If wire is okay, check right solenoid valve (on right carburetor) and replace solenoid valve if necessary. (Scheme 9) Inspect for open or short in Black wire between left solenoid (on left carburetor) and ground, and/or check and replace left solenoid valve (if necessary).

Scheme 10

1. Detach control box from its mounting and open control box lid. (Scheme 3)for control box location. Disconnect lower vacuum hose of vacuum piston control solenoid valve from 3-way fitting and connect a hand-held vacuum pump. (Scheme 10)
2. Disconnect the No. 28 vacuum hose on solenoid valve from hose manifold and connect a vacuum gauge to hose. (Scheme 10) Start engine and warm to normal operating temperature (cooling fan comes on). Apply vacuum. If vacuum is not present on gauge, go to step 4). If vacuum is present on gauge, quickly raise engine speed to 3000 RPM, then close throttle suddenly. If vacuum reading on gauge decreases for a moment, vacuum piston control solenoid valve is okay. If vacuum does not react as specified, go to next step.
3. Turn ignition off and disconnect 8-pin connector on control box. Start engine and raise engine speed to 3000 RPM, then close throttle suddenly. Measure voltage between Yellow (positive) wire terminal and Black (negative) wire terminal on harness. If battery voltage does not decrease momentarily, replace solenoid valve. If voltage does decrease momentarily, check CHECK ENGINE warning light and self-diagnosis LED indicator. If okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.
4. Turn ignition off and disconnect 8-pin connector on control box. Start engine. Measure voltage between Yellow (positive) wire terminal and Black (negative) wire terminal on harness. If battery voltage is present, replace solenoid valve. If battery voltage is not present, measure voltage between Yellow (positive) wire terminal and ground. If battery voltage is still not present, go to next step. If battery voltage is now present, repair open or short in Black wire between control box and ground.
5. Check CHECK ENGINE warning light and self-diagnosis LED indicator. If okay, inspect for open or short in Yellow wire between control box and ECU terminal A6. (Scheme 1)

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING - CARBURETED article.

Scheme 11

1. Disconnect upper vacuum hose of solenoid valve from idle boost throttle controller and connect a vacuum gauge. (Scheme 11) Start engine. If vacuum is present, go to next step. If vacuum is not present, go to step 3).
2. Disconnect 2-pin connector near solenoid valve. If vacuum is still present, replace solenoid valve. If vacuum is not present, A/C signal to ECU should be inspected and corrected. See «A/C SWITCH SIGNAL»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-carbureted) under ENGINE SENSORS & SWITCHES in this article.
3. Turn A/C switch on. Vacuum should now be present. If not, go to next step. If vacuum is present, both A/C idle boost solenoid valve and A/C signal are okay.
4. Disconnect 2-pin connector near solenoid valve. Measure voltage between Red (positive) wire terminal and Black (negative) wire terminal on harness. (Scheme 11) If battery voltage is not present, go to next step. If battery voltage is present, disconnect lower vacuum hose from solenoid valve and connect a vacuum gauge to the disconnected hose. If manifold vacuum is not present, check routing of lower hose to solenoid valve. If manifold vacuum is present, replace solenoid valve.
5. Measure voltage between Red (positive) wire terminal and ground. If battery voltage is now present, repair open or short in Black (negative) wire between solenoid valve and ground. If battery voltage is still not present, voltage from ECU should be inspected and corrected. See «TESTS W/CODES - 2.0L PGM-CARBURETED»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-tests-wcodes-20l-pgm-carbureted) article.

Scheme 12

1. Disconnect No. 18 vacuum hose from vacuum hose manifold and leave disconnected at this time. Disconnect No. 26 (lower) vacuum hose and connect a vacuum pump to hose No. 26. (Scheme 12)
2. Apply vacuum. Vacuum should stabilize at 4-8 in. Hg and pull the opener rod. If not, check linkage for signs of mechanical binding or, if necessary, replace left side carburetor and retest.
3. Cap end of No. 18 hose and again apply vacuum. (Scheme 12) If diaphragm does not pull opener rod, replace left side carburetor and retest.

Scheme 13

1. Disconnect No. 26 vacuum hose from vacuum hose manifold on control box. Connect vacuum pump to hose and apply vacuum. Refer to Fig. (Scheme 13). If gauge registers vacuum, go to next step. If gauge does not register vacuum, check vacuum hose No. 26 for proper connection or leakage. If hose is okay, replace solenoid valve.
2. Check to see if vacuum leaks down. If vacuum leaks down, go to next step. If vacuum does not leak down, repair blockage or pinching in hose. If hose is okay, replace solenoid valve.
3. Connect a "T" fitting with vacuum gauge between vacuum hose No. 26 and vacuum hose manifold. Turn ignition switch to START position and measure vacuum. If there is less than 10 in. Hg, cranking leak solenoid valve is okay.
4. If vacuum reading is greater than 10 in. Hg, turn ignition off. Disconnect 8-pin connector on control box. Measure voltage between Blue/Red (positive) wire terminal and Black (negative) wire terminal on wire harness. Turn ignition switch to START position. If battery voltage is present, replace solenoid valve. If battery voltage is not present, go to next step.
5. Measure voltage between Blue/Red (positive) wire terminal and ground with ignition switch in START position. If battery voltage still not present, inspect for open or short in Blue/Red wire between control box and ignition switch as well as No. 1 fuse. If battery voltage is now present, repair open or short in Black wire between control box and ground.

Scheme 14

1. Start engine and warm to normal operating temperature (cooling fan comes on). Disconnect EACV hose from air cleaner. (Scheme 14)
2. Raise engine speed to 3500 RPM. If vacuum is present at hose, go to next step. If vacuum is not present at hose, check CHECK ENGINE warning light and self-diagnosis LED indicator. If these are okay, replace EACV and retest.
3. Raise engine speed to 3500 RPM again, and then close throttle suddenly. If vacuum is present at hose now, EACV is okay. If not, check CHECK ENGINE warning light and self-diagnosis LED indicator.
4. If either of these lights is on or flashing, go to «TESTS W/CODES - 2.0L PGM-CARBURETED»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-tests-wcodes-20l-pgm-carbureted) article. If these lights are not on or flashing, check hose for proper connection, cracks, blockage, or a disconnected hose. If these are okay, replace EACV and retest.

Scheme 15

1. Start engine and warm to normal operating temperature (cooling fan comes on). Disconnect No. 6 vacuum hose from throttle controller and check engine speed. (Scheme 15) Engine speed should be 1700-2700 RPM for manual transmissions, and 1400-2400 RPM for automatic transmissions.
2. If engine speed is excessively high, adjust engine speed by bending tab near bottom of throttle controller rod. If engine speed does not change, connect a vacuum gauge to No. 6 vacuum hose and check vacuum. If vacuum is present, replace throttle controller and retest. If vacuum is not present, check hose for proper connection, cracks, blockage or a disconnected hose. Replace and repair as necessary. Connect No. 6 vacuum hose and recheck idle speed.

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC TESTING - CARBURETED article.

Scheme 16

1. Detach control box from its mounting and open control box lid. Disconnect lower vacuum hose of solenoid valve from 3-way fitting and connect a vacuum pump. (Scheme 16)
2. Disconnect No. 5 vacuum hose of solenoid valve from vacuum hose manifold and connect a vacuum gauge to hose. (Scheme 16) Start engine and warm to normal operating temperature (cooling fan comes on). Apply vacuum to solenoid valve. If solenoid valve does not hold vacuum, go to step 7). If solenoid valve holds vacuum, go to next step.
3. Raise and support front of vehicle. Block rear wheels and set parking brake. Place transmission in 2nd gear or in "2" position and accelerate to greater than 4000 RPM, then release throttle. If vacuum is present on gauge, go to next step. If vacuum is not present on gauge, turn ignition off and go to step 5).
4. Allow engine to idle. If vacuum is still indicated on gauge, replace solenoid valve. If vacuum no longer registers on gauge, system is okay.
5. Disconnect 8-pin connector on control box. Place transmission in 2nd gear or in "2" position and accelerate vehicle to greater than 4000 RPM, then quickly release throttle. Measure voltage between Red (positive) and Black (negative) wire terminals on harness. If battery voltage is present, replace solenoid valve. If not, go to next step.
6. Measure voltage between Red (positive) wire terminal and ground. If battery voltage is present, repair open or short in Black (negative) wire between control box and ground. If battery voltage is not present, check CHECK ENGINE light and self-diagnostic LED indicator. If these are okay, check for open or short in Red wire between control box and ECU terminal A14.
7. Turn ignition off. Disconnect 8-pin connector on control box. Start engine and measure voltage between Red (positive) wire terminal and Black (negative) wire terminal on harness. If voltage is not present, replace solenoid valve. If voltage is present, check CHECK ENGINE light and self-diagnostic LED indicator. If these are okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.

Scheme 17

Scheme 18

1. With engine at normal operating temperature, remove air cleaner cover and air filter. Start engine and listen for a bubbling noise at air suction port at idle speed. (Scheme 17) Bubbling noise should not be heard. If heard, disconnect No. 5 vacuum hose from air suction valve and connect a vacuum gauge to hose. (Scheme 18) Vacuum should not be present at hose. If vacuum is present, test air suction control solenoid valve. See «AIR SUCTION CONTROL SOLENOID VALVE»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-carbureted__air-suction-control-solenoid-valve) under AIR INJECTION SYSTEM in this article. If vacuum is not present, replace valve and retest.
2. Raise and support front of vehicle. Block rear wheels and set parking brake. Place transmission in 2nd gear or in "2" position and accelerate to greater than 4000 RPM, then release throttle and check for a bubbling noise from air suction port on air cleaner.
3. If noise was not heard, disconnect No. 5 vacuum hose from air suction valve and connect a vacuum gauge. Vacuum should be present when releasing throttle from greater than 4000 RPM. If vacuum is present, replace air suction valve and retest.
4. If vacuum is not present, inspect air suction control solenoid valve. See «AIR SUCTION CONTROL SOLENOID VALVE»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-carbureted__air-suction-control-solenoid-valve) under AIR INJECTION SYSTEM in this article.

Scheme 19

1. Disconnect upper hose of solenoid valve from air cleaner and connect a vacuum pump to hose. (Scheme 19) Disconnect lower hose of solenoid valve and leave disconnected. Start engine and warm to normal operating temperature (cooling fan comes on). Apply vacuum. If valve holds vacuum, go to step 4). If vacuum is not held, go to next step.
2. Turn off engine. Apply vacuum again. If vacuum is held, solenoid valve is okay. If vacuum is not held, turn ignition off. Connect ECU Test Harness between ECU and wire harness. (Scheme 2) Turn ignition switch to ON position. DO NOT start engine. Measure voltage between terminals D2 (positive) and A26 (negative). Refer to Fig. (Scheme 1).
3. If voltage is present, replace solenoid valve. If voltage is not present, check CHECK ENGINE light and self-diagnosis LED indicator. If okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.
4. Turn ignition off. Connect ECU Test Harness between ECU and wire harness. (Scheme 2) Start engine. Measure voltage between terminals D2 (positive) and A26 (negative). (Scheme 1)
5. If battery voltage is present, check for open or short in Green/Yellow wire between solenoid valve and ECU terminal D2. If okay, replace solenoid valve. If battery voltage is not present, check CHECK ENGINE light and self-diagnosis LED indicator. If okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.

Scheme 20

1. Start engine and allow to idle. Disconnect vacuum hose from EGR valve and connect a hand-held vacuum pump to EGR valve. (Scheme 20)
2. Apply 6 in. Hg to EGR valve. If vacuum remains steady and engine dies, EGR valve is working properly. If vacuum does not remain steady and engine does not die, replace EGR valve and retest.
3. If vacuum remains steady but engine does not die, remove EGR valve. Check EGR valve and manifold for blockage. Clean or replace as necessary and retest.

PCV Valve

Check PCV hoses and connection for leaks, cracks or clogging. Start engine and allow to idle. Lightly pinch breather hose between PCV valve and intake manifold with pliers and rag to protect hose. There should be a clicking sound heard or felt from PCV valve. If no sound is heard, check PCV valve grommet for cracks or damage. If grommet is okay, replace PCV valve and retest.

Scheme 21

1. With engine off, disconnect hose from canister PCV fitting. Connect hand-held vacuum pump to canister purge fitting. (Scheme 21) Apply vacuum. Vacuum should remain steady. If not, replace canister and purge fitting and retest. If vacuum remains steady, reconnect hose to canister PCV fitting.
2. On Federal vehicles, raise and support vehicle to allow front wheels to turn and start engine. Raise engine speed (Federal vehicles) to 3500 RPM with transmission in "2" position (or 2nd gear). On California vehicles, start engine and allow engine to idle.
3. Purge side vacuum should drop to zero for both vehicles. If vacuum does not drop, replace canister and retest. (Scheme 21)

Scheme 22

1. Remove air cleaner cover and air filter. Disconnect 2 vacuum hoses from carburetor and connect a hand-held vacuum pump to both hoses. (Scheme 22) Start engine and warm to normal operating temperature. Apply vacuum. If solenoid valve does not hold vacuum, go to step 4). If vacuum is held, go to next step.
2. Turn ignition off. Disconnect Green/Red (positive) and Black (negative) wire connectors located near air cleaner. Refer to Fig. (Scheme 22). Start engine and measure voltage between Green/Red and Black wire terminals. If battery voltage is present, replace solenoid valve. If no voltage is present, go to next step.
3. Measure voltage between Green/Red (positive) wire terminal and ground. If battery voltage is present, repair open or short in Black wire between solenoid valve and ground. If battery voltage is not present, check CHECK ENGINE warning light and self-diagnostic LED indicator. If these are okay, inspect for open or short in Green/Red wire between solenoid valve and ECU terminal A2.
4. Stop engine and apply vacuum with vacuum pump. If solenoid valve holds vacuum now, solenoid valve is okay. If vacuum is still not held, turn ignition off and disconnect Green/Red and Black wire connectors, near air cleaner, and go to next step. (Scheme 22)
5. Turn ignition on and measure voltage between Green/Red (positive) wire terminal and Black (negative) wire terminal. If battery voltage is present, replace solenoid valve. If battery voltage is not present, observe CHECK ENGINE warning light and self-diagnostic LED indicator. If these are okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.

Scheme 23

1. With engine coolant temperature less than 145°F (63°C), disconnect No. 19 vacuum hose at purge control diaphragm valve and connect vacuum gauge to hose. (Scheme 23) Start engine and allow to idle. If vacuum is not present, go to next step. If vacuum is present, test purge cut-off solenoid valve. See «PURGE CUT-OFF SOLENOID VALVE»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-carbureted__purge-cut-off-solenoid-valve) under EMISSION SYSTEMS & SUB-SYSTEMS in this article.
2. Start engine and warm to normal operating temperature (cooling fan comes on). Jack up front of vehicle and support with safety stands. Block rear wheels and set parking brake. Place selector lever in the "2" position or 2nd gear and raise engine speed to 3500 RPM. Vacuum should be present. If so, valve is okay. If vacuum is not present, test purge cut-off solenoid valve. See «PURGE CUT-OFF SOLENOID VALVE»(/honda/prelude/iii-1989-1992/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-carbureted__purge-cut-off-solenoid-valve) under PURGE CONTROL SYSTEM in this article.

Scheme 24

1. Detach control box from its mounting and open control box lid. (Scheme 3)for location. On California vehicles, disconnect lower vacuum hose of solenoid valve from the 3-way joint and connect a vacuum gauge. Trace upper hose to hose manifold on outside of control box and connect a vacuum pump to hose. (Scheme 24)
2. On Federal vehicles, disconnect upper hose on solenoid valve from 3-way joint and connect a vacuum pump to solenoid valve. (Scheme 24)
3. On all vehicles, start engine and apply vacuum. If solenoid valve does not hold vacuum, go to step 4). If vacuum is held, turn ignition off and disconnect 8-pin connector on control box. Start engine and measure voltage between Orange (positive) and Black (negative) wire terminals on engine harness. If voltage is not present, replace solenoid valve. If voltage is present, observe CHECK ENGINE light and self-diagnostic LED indicator. If these are okay, substitute a known good ECU and retest. If symptom goes away, replace original ECU.
4. Warm engine to normal operating temperature (cooling fan comes on). Raise front of vehicle and support with safety stands. Block rear wheels and set parking brake. Place transmission in 2nd gear or in "2" position and accelerate vehicle to 4000 RPM. Apply vacuum. On Federal vehicles, if solenoid valve does not hold vacuum, stop engine go to next step. On California vehicles, if vacuum does not register on vacuum gauge, stop engine and go to next step. If results are correct in either case, solenoid valve is okay.
5. Disconnect 8-pin connector on control box. Start engine, place transmission in 2nd gear or in "2" position and accelerate vehicle to 4000 RPM. Measure voltage between Orange (positive) wire terminal and Black (negative) wire terminal of wire harness. If battery voltage is present, replace solenoid valve. If battery voltage is not present, go to next step.
6. Measure voltage between Orange (positive) wire terminal and ground. If battery voltage is present, repair open or short in Black wire between control box and ground. If battery voltage is not present, observe CHECK ENGINE light and self-diagnostic LED indicator. If these are okay, check for an open or short in Orange wire between control box and ECU terminal A4. Reconnect 8-pin connector.

Scheme 25

1. Remove fuel filler cap. Remove vapor line from fuel tank and connect a "T" fitting, vacuum/pressure pump and vacuum/pressure gauge. (Scheme 25)
2. Slowly apply vacuum with pump while watching gauge. Vacuum should stabilize momentarily at 0.2-0.6 in. Hg. If vacuum stabilizes (valve opens) at less than 0.2 in. Hg, or greater than 0.6 in. Hg, install new valve and retest.
3. Move hose on vacuum pump from vacuum port to pressure port. Ensure vacuum/pressure gauge is set for pressure testing. Slowly pressurize vapor line while watching pressure gauge. Pressure should stabilize at 0.4-1.4 in. Hg. If pressure momentarily stabilizes (valve opens) at this specification, two-way valve is okay. If pressure stabilizes at less than 0.4 in. Hg, or greater than 1.4 in. Hg, install a new valve and retest.

Scheme 26

1. With engine temperature less than 77°F (25°C), disconnect air intake duct and start engine. Air control door should rise. If not, disconnect No. 8 vacuum hose from air control diaphragm and check hose for vacuum using vacuum gauge. (Scheme 26)
2. If vacuum exists, replace air control diaphragm and retest. If vacuum is not present, check No. 8 vacuum hose for proper connection, cracks, blockage, or disconnected hose. Check and replace air bleed valve "A", located in air cleaner chamber, if necessary. Reconnect air intake duct.

Scheme 27

1. Start engine and warm to normal operating temperature. Disconnect air intake duct and immediately check position of air control door. (Scheme 27)
2. Door should be down (fully open). If not, disconnect No. 8 vacuum hose from air control diaphragm and check for vacuum. Vacuum should not be present. If vacuum is not present, replace air control diaphragm and retest. If vacuum is present, replace air bleed valve "A" and retest. Reconnect air intake duct.

See also:
• BASIC TESTING - CARBURETED
• TESTS W/CODES - 2.0L PGM-CARBURETED
• COOLANT TEMPERATURE (TW) SENSOR RESISTANCE
• AIR SUCTION CONTROL SOLENOID VALVE
• PURGE CUT-OFF SOLENOID VALVE