Engine Controls - System/component Tests - Efi Isuzu Amigo I

INTRODUCTION

Before testing separate components or systems, perform procedures in F - EFI BASIC TESTING article in the ENGINE PERFORMANCE Section. Since many computer controlled and monitored components set a trouble code if they malfunction, also perform procedures in G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

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

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 one volt. If reading is greater than one volt, check for open, corrosion and loose connection on ground lead. See ECM GROUND LOCATION table for ECM ground location.

ECM GROUND LOCATION

Power Circuits (Constant Voltage)

1. ECM should always have constant battery voltage to retain memory. On Amigo, Pickup and Rodeo 2.6L, check voltage at Gray wire of 14-pin ECM connector. On Pickup and Rodeo 3.1L, check voltage at Red wire of 32-pin or White wire of 24-pin ECM connector.
2. Voltage is supplied by fuse No. 3, located in fuse block at left side of dash.
3. On Trooper 2.6L, check voltage at Gray wire of 14-pin ECM connector. Voltage is supplied by fuse No. 6, located in fuse box at left side of engine compartment.
4. On Trooper 2.8L, check voltage at White wire of 32-pin ECM connector. Voltage is supplied by Green fusible link, located in fusible link box at right front corner of engine compartment.

Power Circuits (Ignition Voltage)

1. ECM should always have battery voltage when ignition is on. On Amigo, Pickup and Rodeo, check voltage at Light Green/Red and Light Green/Black wires of 18-pin ECM connector. Voltage is supplied by ECM relay, located in fuse/relay box at right side of engine compartment.
2. White/Blue wire of main relay receives voltage from fuse No. 1 in fuse/relay box at right corner of engine compartment. Violet wire of main relay receives voltage from fuse No. 8, located in fuse block at left side of dash.
3. On Trooper, check voltage at Black/White wire of 18-pin (24-pin on 2.8L) ECM connector. Voltage is supplied by main relay, located on right side of engine compartment. White wires at main relay should have constant battery voltage and Black/Yellow wire should have voltage only if ignition is on.
4. Voltage to White wires is supplied by Green fusible link, located in fusible link box at right front corner of engine compartment. Black/Yellow wire receives voltage from fuse No. 14, located in fuse block on left side of engine compartment.

A/C SWITCH

See A/C CLUTCH CONTROL under MISCELLANEOUS CONTROLS.

Amigo, Pickup, Rodeo & Trooper 2.6L

1. Pull back rubber boot on airflow sensor harness connector. With ignition off, check for voltage between Black wire terminal and ground. Voltage should be less than.2 volt. If voltage is incorrect, check wiring to ECM. Repair as necessary.
2. Turn ignition on. With engine off, check voltage between Red wire (Amigo, Pickup and Rodeo) or Light Green/Red wire (Trooper) and ground. (Scheme 143)or (Scheme 144). Voltage should be 10-14 volts. With ignition off, voltage should be less than.2 volt. If voltage is incorrect, check wiring to ECM. Repair as necessary. NOTE: Airflow sensor malfunctions may also set trouble Codes 61 and 62. For additional testing information, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.
3. With engine idling, check voltage between White wire (Amigo, Pickup and Rodeo) or Light Green/White wire (Trooper) and ground. Voltage should be.5-1.5 volts. If voltage is incorrect and voltage in steps 1) and 2) was okay, replace airflow sensor.
4. Check airflow sensor by-pass circuit. (Scheme 145) If circuit is dirty or contaminated, clean it with carburetor cleaner. DO NOT let carburetor cleaner touch electrical or rubber components.

Scheme 143

Scheme 144

Scheme 145

COOLANT TEMPERATURE SENSOR

1. Unplug coolant temperature sensor. On Amigo, Pickup, Rodeo and Trooper (2.6L), sensor is located on right side of engine, below intake manifold. Sensor connector contains Black and Green/Yellow wires.
2. On Trooper 2.8L, sensor is located on front of intake manifold, near throttle body.
3. On all models, check resistance between sensor terminals at specified temperature. See «COOLANT TEMP SENSOR RESISTANCE SPECIFICATIONS»(/isuzu/amigo/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-efi) table. Replace sensor if not within specification.

Note. Coolant temperature sensor malfunctions may also set trouble Codes 14 and 15. For additional testing information, refer to the appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

COOLANT TEMP SENSOR RESISTANCE SPECIFICATIONS

For testing information, see CODE 41 in appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section. If crank angle sensor malfunctions, Code 41 will set. Replace distributor assembly if wiring circuit is okay. (Scheme 146)or (Scheme 147).

Scheme 146

Scheme 147

Pickup & Rodeo 3.1L; Trooper 2.8L

To test crank signal, see DIAGNOSTIC CHARTS, CHART C-1B, CHECKING CRANK SIGNAL.

EGR TEMPERATURE SENSOR

See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS & SUB-SYSTEMS.

Pickup 3.1L, Rodeo 3.1L & Trooper 2.8L

See TIMING CONTROL SYSTEMS under IGNITION SYSTEMS.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

MAP sensor is located on left side of air cleaner (Pickup & Rodeo 3.1L; Trooper 2.8L) and on right side of engine compartment (Amigo, Pickup, Rodeo & Trooper 2.6L). To diagnose MAP sensor problem, see DIAGNOSTIC CHARTS, CHART C-1D, MAP SENSOR OUTPUT.

Note. A malfunctioning MAP sensor may set trouble Codes 33 and 34 (Amigo, Pickup, Rodeo & Trooper). For additional sensor testing procedures, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

O2 SENSOR

1. Start engine, and warm to operating temperature. Ensure vehicle is operating in closed loop. Unplug O2 sensor connector at sensor.
2. Using Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, connect DVOM (on voltmeter scale) between ground and O2 sensor connector (sensor side).
3. Place a short jumper wire in sensor lead (computer side). While holding jumper wire in one hand, alternately touch negative battery terminal and then positive terminal with other hand. DO NOT touch sensor lead directly to battery.
4. Monitor DVOM reading. When negative battery terminal is touched, O2 sensor output voltage should increase (up to one volt). When positive battery terminal is touched, O2 sensor output voltage should drop (as low as .1 volt). If O2 sensor does not respond as indicated, replace sensor.

PARK/NEUTRAL SWITCH

Disconnect switch connector at transmission, and note terminal identification. (Scheme 148) Using ohmmeter, check continuity between specified terminals in proper gear positions. See PARK/NEUTRAL SWITCH CONTINUITY SPECIFICATIONS table. Replace switch if continuity is not as specified.

Scheme 148

PARK/NEUTRAL SWITCH CONTINUITY SPECIFICATIONS

THROTTLE POSITION SENSOR (TPS)

1. Unplug TPS harness at sensor. Connect ohmmeter between wire terminals Blue/Red and Green/Yellow wires.
2. Resistance should vary smoothly as throttle is moved from idle to wide open throttle. Resistance reading should not drop or climb suddenly as continuity is checked. Replace sensor if defective.
3. To check sensor operating voltage, connect TPS harness. Sensor operating voltage may be monitored at ECM with ignition on. Note ECM location. See ECM LOCATION table. ECM LOCATION Model Location Amigo, Pickup & Rodeo Behind Left Kick Panel Trooper Below Center Console, Between Seats
4. On all models, turn ignition on. DO NOT start engine. Using digital voltmeter, backprobe ECM connector terminals to check if 5-volt TPS reference signal is present. Reference signal should be present at ECM terminals: Amigo, Pickup, Rodeo and Trooper (2.8L) - C13 (Blue/Red wire). Trooper 2.6L - C200 (Gray/Black wire).
5. If 5-volt reference signal is not present, check for short to ground in 5-volt reference line from ECM to TPS. If no short is present, ECM is defective.
6. If 5-volt reference signal is present, test TPS input signal at appropriate ECM terminal. Connect negative voltmeter probe to ground. Backprobe ECM terminal with positive voltmeter probe at following ECM wire terminals: Amigo, Pickup, Rodeo and Trooper (2.8L) - C13 (Blue/Red wire). Trooper 2.6L - (Gray/Black wire).
7. With engine running, voltage should read approximately .5 volt at idle and increase to approximately 5 volts at wide open throttle. If voltage reading is incorrect, check wiring to TPS. If wiring is okay, replace TPS.

Note. Code 21 or 22 may set if a malfunction in TPS exists. For additional TPS testing procedures, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

Note. Trooper 2.6L uses throttle position sensor and throttle valve switch on A/T models. M/T models uses only throttle valve switch.

1. Disconnect throttle valve switch. Note terminal identification. (Scheme 149) Check throttle valve switch terminals for proper continuity. With throttle at idle, continuity should be present between terminals "I" and "P", but not between terminals "P" and "F."
2. At wide open throttle, continuity should be present between terminals "P" and "F", but not between terminals "I" and "P."
3. No continuity should exist between terminals "I" and "P" or "P" and "F" with throttle between idle and wide open position. Replace throttle valve switch if defective.

Scheme 149

Amigo, Pickup & Rodeo

1. Remove instrument cluster and combination meter from dash. Using ohmmeter, check continuity across vehicle speed sensor (VSS) terminals. (Scheme 150)
2. Rotate speedometer shaft slowly and note if reading alternates from continuity to an open circuit. Replace speedometer assembly if VSS is defective.

Note. If a problem develops with vehicle speed sensor, ECM will set Code 63. For additional testing procedures, refer to the appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

Scheme 150

Trooper

1. With instrument cluster removed, use ohmmeter to check continuity across vehicle speed sensor (VSS) terminals. (Scheme 151)
2. Rotate speedometer shaft slowly and note if reading alternates from continuity to an open circuit 4 times per revolution. Replace speedometer assembly if VSS is defective.

Scheme 151

Note. If a problem develops with vehicle speed sensor, ECM will set Code 24. For additional testing procedures, refer to the appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

Fuel Pump & Main Relays

Detailed test procedures for testing relays are not available from manufacturer. These relays should be tested in usual manner. Use (Scheme 152) and (Scheme 153) as examples.

Scheme 152

Scheme 153

Air Regulator Solenoid

See IDLE CONTROL SYSTEM.

IAC Motor

This component is called Idle Air Control (IAC) valve. See IDLE CONTROL SYSTEM .

Electronic Spark Control Module

See TIMING CONTROL SYSTEMS under IGNITION SYSTEM.

Scheme 154

FUEL DELIVERY

Note. For fuel system pressure testing, see appropriate F - EFI BASIC TESTING article in the ENGINE PERFORMANCE Section.

Pressure Regulator

1. Install fuel pressure gauge on fuel rail. Use care when installing fuel pressure gauge, as fuel lines are under pressure. Disconnect vacuum hose at pressure regulator.
2. Start engine and note fuel pressure. Ensure vacuum supply exists at vacuum line. Reconnect vacuum hose. Fuel pressure should decrease slightly. Replace pressure regulator if fuel pressure does not change.

Pressure Regulator Vacuum Switching Valve (VSV) (2.6L)

1. On Amigo, Pickup and Rodeo, VSV is located on right side of engine compartment, near battery. On Trooper, VSV is located on right side of engine compartment, near charcoal canister. NOTE: On all models, pressure regulator VSV and canister purge VSV share a 4-pin electrical connector and are mounted side-by-side. Ensure VSV hoses are connected to pressure regulator.
2. Disconnect electrical connector. Connector contains Black/White and Light Green wires. Wires for pressure regulator VSV are Blue and Black.
3. Using ohmmeter, check resistance between Blue and Black wire terminals of VSV. Replace VSV if resistance is not approximately 35 ohms. Install connector.
4. To check VSV operation with vehicle not running, disconnect electrical connector. Apply battery voltage to Black wire, and connect ground wire to Blue wire. Replace VSV if operation of vacuum ports does not change.
5. To check VSV operation with vehicle running, install fuel pressure gauge on fuel rail. WARNING: Use care when installing fuel pressure gauge, as fuel lines are under pressure.
6. Start engine and note fuel pressure. Fuel pressure should be approximately 35 psi (2.5 kg/cm 2 ). Disconnect electrical connector from VSV.
7. Apply battery voltage to Black wire, and connect ground wire to Blue wire of VSV. Fuel pressure should be approximately 42 psi (2.9 kg/cm 2 ). Replace VSV if pressure does not increase.

Note. If a problem develops with pressure regulator VSV, ECM will set Code 25 or 53. For additional testing procedures, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

Dropping Resistor (2.6L)

1. Unplug dropping resistor wire connector. Dropping resistor is located on right rear corner of engine compartment, near cruise control actuator.
2. Using ohmmeter, measure resistance between center terminal (White wire) of resistor connector and remaining terminals. Standard resistance at all terminals should be 5-7 ohms at room temperature. If any measurement deviates from standard value, replace dropping resistor.

Scheme 155

1. Warm engine to operating temperature. Turn ignition off. Unplug throttle valve switch wire connector. NOTE: Throttle valve switch and throttle position sensor are mounted on throttle body throttle shaft. M/T models use throttle valve switch. A/T models use throttle position sensor and throttle valve switch.
2. Insert a fine wire into upper (idle) terminal. Reconnect throttle valve switch connector with fine wire partially pulled outward. (Scheme 155)
3. Start engine, and operate at 2000-2500 RPM. Connect battery voltage to fine wire installed on throttle valve switch. When battery voltage is applied, engine speed should decrease to approximately 1250 RPM. Engine surging may occur, which is normal during test procedure.

Note. Fuel cut-off and fuel injection reactivation is controlled by throttle valve switch. See FUEL-CUT SPECIFICATIONS table for fuel-cut operating conditions.

FUEL-CUT SPECIFICATIONS

Fuel Injectors

1. Unplug fuel injector harness at injector. Using ohmmeter, measure resistance across terminals. Replace fuel injectors if resistance is not within specification. See «FUEL INJECTOR RESISTANCE SPECIFICATIONS»(/isuzu/amigo/i-1989-1994/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-efi) table.
2. With engine running, check fuel injector operating noise. Normal operation of injectors is indicated if a regular "click" is heard, which varies with engine speed. If "click" is not heard, replace injector.

FUEL INJECTOR RESISTANCE SPECIFICATIONS

Fuel Injector Balance Test

1. Connect fuel pressure gauge to fuel rail. Disconnect vacuum hose at pressure regulator. Turn ignition on and note fuel pressure. Fuel pressure should be 35-38 psi (2.5-2.7 kg/cm 2 ). Start engine, and reconnect vacuum hose. Fuel pressure should slightly decrease. NOTE: Fuel pressure must be correct before proceeding with injector balance test.
2. With ignition off, unplug harness connectors at all injectors. Install Injector Tester (J-34730-3) on one injector. Turn ignition on, and bleed off air in fuel pressure gauge. Fuel pump should operate for approximately 2 seconds.
3. Turn ignition off for 10 seconds. Turn ignition on with engine off. Turn injector on by pressing button on injector tester. Note pressure drop the instant gauge needle stops. Pressure may increase for a few seconds after initial pressure drop. CAUTION: To prevent flooding, entire test should not be repeated more than once.
4. Injector pressure drop should be nearly the same for all injectors. Replace any injector with more than a 1.45 psi (10 kg/cm 2 ) difference from other injectors.

See A/C CLUTCH CONTROL under MISCELLANEOUS CONTROLS.

Scheme 156

1. Check operation of air regulator with engine cold. Start engine and note if idle speed is higher than normal after initial start. If idle speed is not higher, proceed to step 4).
2. As engine temperature increases, engine idle speed should stabilize. Check air regulator for leakage. Disconnect hose between air regulator and throttle valve body at throttle valve body side. Plug throttle body fitting end. (Scheme 156)
3. Start engine, and check for variation in engine speed by closing and opening end of air regulator hose. Variation in engine speed should be less than 50 RPM. Replace air regulator if variation in engine speed is more than specification.
4. If fast idle speed was not higher than normal on initial engine start, disconnect air regulator harness connector at air regulator. On Amigo, Pickup and Rodeo, air regulator is located on right rear of engine, below intake manifold. On Trooper, air regulator is located on right side of engine, in front of starter.
5. Using an ohmmeter, measure resistance between air regulator terminals. Resistance should be 38-42 ohms (Amigo, Pickup and Rodeo) or 45-49 ohms (Trooper). Replace air regulator if resistance is not within specification. If resistance is within specification, proceed to step 6).
6. Turn ignition on. Using a voltmeter, check for voltage at air regulator harness connector. If voltage is present, replace air regulator. If voltage is not present, check wiring to air regulator and fuel pump relay.

IDLE AIR CONTROL VALVE (AMIGO, PICKUP, RODEO & TROOPER)

For Idle Air Control (IAC) valve testing, see DIAGNOSTIC CHARTS, CHART C-2C, IDLE AIR CONTROL VALVE.

See ENGINE SENSORS & SWITCHES .

IGNITION SYSTEM

Note. For basic ignition checks, see appropriate F - EFI BASIC TESTING article in the ENGINE PERFORMANCE Section.

Electronic Spark Control (Pickup & Rodeo 3.1L, Trooper 2.8L)

To test ESC system, see DIAGNOSTIC CHARTS, CHART C-5, ESC SYSTEM. ESC module is located on right side fenderwell and contains a 5-pin connector.

Note. If a problem develops with ESC, ECM will set Code 43. For additional testing procedures, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

Electronic Spark Timing (Pickup & Rodeo 3.1L, Trooper 2.8L)

1. To check system operation, check timing at 1500 RPM with ALDL ungrounded. Locate ALDL connector.
2. ALDL is located below left side of instrument panel (Pickup and Rodeo) or below center console (Trooper). (Scheme 157)
3. Install jumper wire between terminals "A" and "B" of ALDL connector. (Scheme 157) Note timing at 1500 RPM. If timing changes, system is operating correctly.

Note. If a problem develops with EST, ECM will set Code 42. For additional testing procedures, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

Scheme 157

Power Transistor (Amigo, Pickup, Rodeo & Trooper 2.6L)

1. Disconnect high-tension coil wire at distributor. Install Spark Tester (J-26792) on end of coil wire. If spark tester is not available, coil wire can be held approximately 1/4" away from metal surface using insulated pliers while testing for spark.
2. Raise and support vehicle. Remove right front tire. Disconnect rubber cover from inner fender. Remove power transistor from bottom of intake manifold. Disconnect power transistor electrical connector.
3. Install a 1.5-volt dry cell battery between connector and power transistor. (Scheme 158)
4. With dry cell battery connected, ground power transistor to vehicle frame. Turn ignition on.
5. Disconnect and reconnect jumper lead at power transistor connector. Verify spark is present at spark tester or between coil wire and metal surface. Repeat test procedure several times. Replace power transistor if spark is not present.

Note. If a problem develops with power transistor, ECM will set Code 25 or 53. For additional testing procedures, refer to the appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

Scheme 158

Air Management System (Trooper 2.8L)

To check air management system, see DIAGNOSTIC CHARTS, CHART C-6, AIR MANAGEMENT SYSTEM.

Air Management Valve (Amigo, Pickup & Rodeo 2.6L)

1. Warm engine to normal operating temperature. With engine idling, ensure secondary air is passing from silencer on air management valve. (Scheme 159)
2. Stop engine. Disconnect air hose at check valve, and plug opening of check valve. Start engine and note air passes from air management valve for a few seconds. After a few seconds, air should pass from silencer. Replace air management valve if defective. Air management valve will operate only under specified conditions. (Scheme 160)

Scheme 159

Scheme 160

Air Switching Valve (Trooper 2.6L)

1. Warm engine to normal operating temperature. With engine idling, ensure secondary air is diverted from silencer, located on air cleaner. (Scheme 161)
2. Disconnect vacuum hoses "X" and "Z" from air switching valve. Disconnect air hose at check valve, and plug check valve opening.
3. Disconnect vacuum hose "Y", and connect hose to air switching valve vacuum hose port "X." Ensure secondary air passes from air switching valve at check valve hose. Replace air switching valve if defective. Air switching valve will operate only under specified conditions. (Scheme 162)

Scheme 161

Scheme 162

Air Switching Valve VSV (Trooper 2.6L)

1. Disconnect electrical connector from VSV, located on left side of engine compartment, near brake booster. Apply battery voltage to VSV. Ensure air does not pass freely between ports "X" and "Y" and passes freely between ports "Y" and "Z". (Scheme 163)
2. Disconnect battery voltage from VSV. Ensure air passes freely between ports "X" and "Y" and does not pass freely between ports "Y" and "Z". Replace VSV if defective.

Scheme 163

Check Valve (Amigo, Pickup & Rodeo 2.6L; Trooper)

1. Remove check valve from air manifold. Blow air into air pump side of check valve. Air should pass freely to manifold side of check valve.
2. Blow air into manifold side of check valve. Air should not pass to air pump side of valve. Replace check valve if defective.

Backpressure Transducer (BPT) (Amigo & Pickup 2.6L - Federal; Rodeo & Trooper 2.6L)

Disconnect BPT vacuum hoses. Blow air into Black port (bottom port). Ensure air does not pass through transducer. When blowing on vacuum line to EGR at transducer, ensure air passes through transducer and out air filter. Replace assembly if defective.

Duty Solenoid (Amigo & Pickup 2.6L - California)

Testing procedure is not available from manufacturer.

EGR Control Module (Trooper 2.8L)

Testing procedure is not available from manufacturer.

EGR System (Amigo & Pickup 2.6L - Federal; Rodeo & Trooper (2.6L)

Testing procedure is not available from manufacturer. System will operate only under specified conditions. (Scheme 164)

Scheme 164

EGR System (Amigo & Pickup 2.6L - California)

1. System will operate only under specified conditions. (Scheme 165) To test system operation, ensure engine coolant temperature is less than 59°F (15°C). Install tachometer. Disconnect vacuum hose at EGR valve, and connect vacuum gauge to vacuum hose.
2. Start engine. Vacuum gauge should read zero at all engine speeds. With engine at normal operating temperature, vacuum gauge should read zero at idle. Vacuum gauge should start to indicate vacuum at 3500 RPM.
3. Reconnect vacuum hose to EGR valve. Ensure EGR valve diaphragm moves when engine is at 2000 RPM.

Scheme 165

EGR System (Trooper 2.8L)

EGR solenoid is located inside EGR control module, on rear of right cylinder head. To check EGR system, see DIAGNOSTIC CHARTS, CHART C-7, EGR SYSTEM.

Note. Ensure Code 24 or 34 is not stored before testing EGR system. See appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

EGR Temperature Sensor (Amigo & Pickup 2.6L - Federal; Rodeo & Trooper 2.6L)

If a malfunction in EGR temperature sensor occurs, ECM will set Code 32 or 34. For EGR temperature sensor testing procedure, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

EGR Vacuum Switching Valve (VSV) (Amigo & Pickup 2.6L Calif)

Apply 12 volts to VSV terminals. Air should flow freely through ports. Disconnect voltage. Air should not flow through ports. Replace VSV if defective.

EGR Vacuum Switching Valve (VSV) (Rodeo 2.6L)

Apply battery voltage to VSV terminals. Air should flow freely between ports "Y" and "Z" and not between ports "X" and "Y". (Scheme 166) Disconnect voltage. Air should flow between ports "X" and "Y" and not between ports "Y" and "Z". Replace VSV if defective.

Scheme 166

EGR Valve

1. Using a vacuum pump, apply vacuum to EGR valve diaphragm. EGR valve diaphragm should hold vacuum. Ensure vacuum does not leak down and EGR valve diaphragm moves to a fully open position.
2. Inspect EGR valve diaphragm for cracking. Check valve and seat for deformation and carbon deposits. Replace EGR valve if defective.

Thermal Vacuum Valve (TVV) (Amigo & Pickup 2.6L - Federal; Rodeo & Trooper 2.6L)

Disconnect TVV vacuum hoses. With engine coolant temperature less than 95°F (35°C), air should not pass through valve. With coolant temperature greater than 129°F (54°C), air should pass through valve. Replace TVV if defective.

EVAPORATIVE EMISSION SYSTEM (EVAP)

Note. Canister purge vacuum solenoid valve is also known as canister purge vacuum switching valve.

Canister Purge Vacuum Switching Valve (VSV) (2.6L)

1. Disconnect canister purge VSV harness connector, located on left fender panel, near canister. VSV harness connector wire colors are Black/White and Green/White. DO NOT confuse VSV connector with fuel pressure regulator connector.
2. Apply battery voltage to Black wire terminal of VSV connector, and ground Blue wire terminal. Ensure air does not flow freely between ports "Y" and "Z". Air should flow freely between ports "X" and "Y". (Scheme 167)
3. Disconnect battery voltage from VSV connector. Ensure air flows freely between ports "Y" and "Z". Air should not flow freely between ports "X" and "Y". If VSV does not perform as indicated, replace canister purge VSV.

Scheme 167

Canister Purge Control Valve (2.6L)

1. With engine off, disconnect vacuum hose from lower port "A". (Scheme 168)and (Scheme 169). Connect a short section of hose to lower port "A", and blow air into it. Ensure air does not flow freely into charcoal canister.
2. Connect hand-held vacuum pump to lower port "A", and apply 15 in. Hg. Purge control valve should hold vacuum. If it does not hold vacuum, replace purge control valve. With vacuum holding at port "A", install second hand-held vacuum pump to purge control valve port. Gradually apply vacuum to purge control valve port. Purge control valve should open at 7.1-8.7 in. Hg. Replace purge control valve if it does not perform as indicated.
3. Start engine, and let idle. Disconnect vacuum hose from port "C". Ensure vacuum is not present at ports "C" and "D". If vacuum is present at idle, check for improperly routed vacuum hoses or defective purge control valve.

Testing Canister Purge Control Valve (2.6L) (1 of 2) 122403Courtesy of Isuzu Motor Co. Scheme 168

Scheme 169

In-Tank Pressure Control Valve (P/U & Rodeo 3.1L; Trooper 2.8L)

1. In-tank pressure control valve, located in fuel tank sending unit, is a combination roll-over, integral pressure and vacuum relief valve.
2. If vapor pressure in tank exceeds 1 in. Hg, valve opens and allows vapors to vent to canister. In-tank pressure control valve provides pressure relief to protect against pressure build-up in fuel tank and roll-over protection in an accident.

Thermostatic Vacuum Switch (TVS) (Pickup & Rodeo 3.1L; Trooper 2.8L)

TVS is installed in intake manifold coolant passage. TVS is closed until coolant temperature reaches 115°F (46°C), when it opens and purges vapor canister. (Scheme 170)

Scheme 170

PCV Valve

1. With engine running, remove PCV valve from rocker cover. Place thumb over end of valve to check for vacuum. If vacuum is present, go to step 3). If no vacuum is present, remove PCV valve. If vacuum is present when valve is removed or engine dies, replace valve.
2. If engine RPM changes little or does not change after removing valve from hose, replace vacuum hose between throttle body or intake manifold and PCV valve.
3. Turn ignition off. Remove PCV valve. Blow air into PCV valve from cylinder head side of valve. Ensure air flows through valve easily. DO NOT suck air through valve.
4. Blow air into intake manifold side of PCV valve. Ensure air does not flow through other side of valve. If valve does not function as indicated or valve does not rattle when shaken, replace PCV valve.

With engine off and air cleaner installed, TAC snorkel damper door should be open. When cold engine is first started, damper door should close to outside air. If door fails to operate, perform VACUUM MOTOR CHECK and TEMPERATURE SENSOR CHECK.

Vacuum Motor Check

Check all related vacuum hoses for kinks, breaks and plugs. With engine off, disconnect vacuum hose at TAC vacuum motor. Using hand-held vacuum pump, apply 7 in. Hg to motor. Damper door should close off intake (cold air) end of snorkel. If damper door does not close, check linkage and door for binding. If no problem is found, replace vacuum motor on air cleaner.

Temperature Sensor Check

1. With engine temperature less than 86°F (30°C), place a thermometer inside air cleaner as close to sensor as possible. Reinstall air cleaner cover. Start engine, and let idle.
2. Damper door should close immediately. If it does not, check vacuum hoses to sensor from throttle body and to vacuum motor from sensor. If vacuum hoses and vacuum motor are okay, replace sensor.
3. Observe when damper door opens snorkel passage. Remove air cleaner cover, and note thermometer. Temperature should be approximately 131°F (55°C). If temperature is not as indicated, replace sensor.

MISCELLANEOUS CONTROLS

Note. Although some of the controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.

For diagnosis of A/C clutch control, see DIAGNOSTIC CHARTS, CHART C-10, A/C CLUTCH CONTROL DIAGNOSIS.

CHART C-1B, CRANK SIGNAL (P/U & RODEO 3.1L; TROOPER 2.8L)

Crank signal is a 12-volt signal to ECM during cranking to allow enrichment and cancel diagnostics until engine is running or 12-volt signal is no longer on circuit.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for normal cranking voltage to ECM terminal C9. Test light should be on during cranking.
2. Checks if source of blown fuse was a faulty ECM.

Scheme 171

Scheme 172

CHART C-1D, MAP SENSOR OUTPUT

Note. Test numbers refer to test numbers on diagnostic chart.

1. This step checks MAP sensor output voltage to ECM. Without engine running, this voltage represents a barometric reading to ECM.
2. Applying a vacuum reading of 10 in. Hg to MAP sensor should cause voltage to be 1.2 volts less than voltage in step 1). When applying vacuum to sensor, change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3. This step checks vacuum hoses to sensor for leaks and restrictions. Ensure no other vacuum devices are connected to MAP sensor hose.

MAP SENSOR VOLTAGE (1)

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CHART C-2C, IDLE AIR CONTROL VALVE

Note. Test numbers refer to test numbers on diagnostic chart.

1. Continue with test, even if engine will not idle. If idle is too low, Scan tester will display 80 or more counts. If idle is high, it will display zero counts. Occasionally, an erratic or unstable idle may occur. Engine speed may vary 200 RPM or more up and down. Disconnect IAC valve. If condition is unchanged, IAC is not at fault.
2. When engine was stopped, IAC valve plunger retracted (more air) to a fixed park position for increased airflow and idle speed during next engine start. A Scan tester will display 100 or more counts. When performing this test, immediately note RPM on start-up. On a warm engine, RPM will decrease rapidly.
3. Ensure IAC valve is disconnected before testing. Test light will confirm ECM signals with a steady or flashing light on all circuits.
4. There is a remote possibility a circuit is shorted to voltage, which would have been indicated by a steady light. Disconnect ECM, and turn ignition on. Probe terminals to check for this condition.

Diagnostic Aids

A slow unstable idle may be caused by a system problem which cannot be overcome by IAC valve. Scan tester counts will be more than 80 counts if too low and will be zero counts if too high.

If idle is too high, stop engine. Turn ignition on, and ground diagnostic test terminal. Wait 30 seconds for IAC valve to seat, then disconnect IAC valve. Remove ground from diagnostic test terminal, and start engine. If idle speed is more than 450 RPM in Drive, locate and correct vacuum leak. If RPM is less than 450 RPM, adjust minimum idle speed or correct other conditions affecting idle speed.

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CHART C-5, ESC SYSTEM (PICKUP AND RODEO 3.1L)

Electronic Spark Control (ESC) is accomplished using an ESC module which sends a voltage signal to ECM. As knock sensor detects engine knock, voltage from ESC module to ECM is shut off. This signals ECM to retard timing (if engine speed is greater than 900 RPM).

Note. Test numbers refer to test numbers on diagnostic chart.

1. If a Code 43 is not set but a knock signal is indicated while running at 1500 RPM, listen for an internal engine noise. Under a no-load condition, detonation should not exist. If a knock is indicated, an internal engine problem may exist.
2. Usually a knock signal can be generated by tapping on right exhaust manifold. This test can also be performed at idle. Test number 1) was run at 1500 RPM to determine if a constant knock signal which would affect engine performance was present.
3. This tests whether knock signal is due to sensor, a basic engine problem or ESC module.
4. If module ground circuit is faulty, ESC module will not function correctly. Test light should illuminate, indicating ground circuit is okay.
5. Touching a test light from 12 volts to circuit No. 496 should generate a knock signal. This will determine whether knock sensor is at fault or ESC module cannot recognize a knock signal.

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CHART C-5, ESC SYSTEM (TROOPER 2.8L)

Electronic Spark Control (ESC) is accomplished using an ESC module which sends a voltage signal to ECM. As knock sensor detects engine knock, voltage from ESC module to ECM is shut off and this signals ECM to retard timing (if engine speed is greater than 900 RPM).

Note. Test numbers refer to test numbers on diagnostic chart.

1. If a Code 43 is not set but a knock signal is indicated while running at 1500 RPM, listen for an internal engine noise. Under a no-load condition, detonation should not exist. If a knock is indicated, an internal engine problem may exist.
2. Usually a knock signal can be generated by tapping on right exhaust manifold. This test can also be performed at idle. Test number 1) was run at 1500 RPM to determine if a constant knock signal which would affect engine performance was present.
3. This tests whether knock signal is due to sensor, a basic engine problem or ESC module.
4. If module ground circuit is faulty, ESC module will not function correctly. Test light should illuminate, indicating ground circuit is okay.
5. Contacting terminal "A" of ESC module harness with a test light to 12 volts should generate a knock signal. This will determine whether knock sensor is faulty or if ESC module cannot recognize a knock signal.

If ESC system checks okay but detonation is complaint, refer to H - EFI TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

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CHART C-6, AIR MANAGEMENT SYSTEM (2.8L)

Air management is controlled by air management valve. This valve directs air into exhaust ports or air cleaner. During cold starts, ECM completes ground circuit and air management valve is energized. Air management valve directs air into exhaust ports. As coolant temperature increases or system goes into closed loop, ECM opens ground circuit. Air management valve is de-energized and air is directed into air cleaner.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This is a system performance check. When vehicle goes into closed loop, air will switch from ports and divert to air cleaner.
2. This tests for a grounded electric divert circuit. Normally, system light will be off.
3. This checks for an open control circuit. Grounding diagnostic terminal will energize this solenoid if ECM and circuits are normal. In this step, if test light is on, circuits are normal and fault is in valve connections or valve.
4. This checks for voltage from battery through a fuse to solenoid.

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CHART C-7, EGR SYSTEM (2.8L)

ECM operates a solenoid in EGR control module to control vacuum to EGR valve. This solenoid is normally closed. ECM provides a ground to solenoid and solenoid opens, allowing vacuum to EGR valve.

ECM controls EGR based on following inputs

1. Engine coolant temperature is greater than 77°F (25°C).
2. TPS is off idle.
3. MAP sensor readings.

Note. Test numbers refer to test numbers on diagnostic chart.

1. With ignition on and engine off, solenoid should not be energized and vacuum should not pass to EGR valve.
2. Grounding diagnostic terminal will energize solenoid, allowing vacuum to pass to EGR valve.
3. This test checks for plugged EGR passages. If passages are plugged, engine may have severe detonation on acceleration.
4. Solenoid is not energized in Park or Neutral. This test will determine if switch input is being received by ECM.

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CHART C-10, A/C CLUTCH CONTROL DIAGNOSIS (2.8L)

A/C clutch control relay is ECM-controlled to delay A/C clutch engagement approximately .4 second after A/C is turned on. This allows IAC to adjust engine RPM before A/C clutch engages. ECM also causes relay to disengage A/C clutch during WOT, when high power steering pressure is present or if engine is overheating. A/C clutch control relay is energized when ECM provides a ground for circuit Green/Black wire circuit No. 03.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks for low refrigerant or dual pressure switch as cause for no A/C.
2. This and following tests check for a faulty A/C control relay.
3. This and following tests check for an open in ECM wiring or a faulty ECM.

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CHART C-10, A/C CLUTCH CONTROL DIAGNOSIS (3.1L)

A/C clutch control relay is ECM-controlled to delay A/C clutch engagement approximately .4 second after A/C is turned on. This allows IAC to adjust engine RPM before A/C clutch engages. ECM also causes relay to disengage A/C clutch during WOT, when high power steering pressure is present or if engine is overheating. A/C clutch control relay is energized when ECM provides a ground for Blue/Green wire at terminal A2.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks for low refrigerant or dual pressure switch as cause for no A/C.
2. This and following tests check for a faulty A/C control relay.
3. This and following tests check for an open in ECM wiring or a faulty ECM.

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Scheme 188

See also:
• COOLANT TEMP SENSOR RESISTANCE SPECIFICATIONS