Engine Controls - System/component Tests - Efi Isuzu Impulse II

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.

SECONDARY AIR SYSTEM DOHC

To check secondary air system, proceed to DIAGNOSTIC CHARTS, CHART C-2D, SECONDARY AIR SYSTEM.

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)

ECM should always have constant battery voltage to retain memory. Check voltage at Red/White wires of 24-pin and 32-pin ECM connectors. Voltage is supplied by ECM fuse, located in fuse/relay box at left front corner of engine compartment.

Power Circuits (Ignition Voltage)

ECM should always have battery voltage when ignition is on. Check voltage at Red/Green wire of 24-pin ECM connector. Voltage is supplied by main relay, located in fuse relay box in front of left strut tower. Ensure voltage is present at Black/Yellow wire of main relay. Main relay receives voltage from fuse No. 11 of junction block, located at left kick panel.

A/C SWITCH

See A/C CLUTCH CONTROL under MISCELLANEOUS CONTROLS.

COOLANT TEMPERATURE SENSOR

Unplug coolant temperature sensor. Sensor is located on left side of engine, in coolant outlet. Check resistance between sensor terminals at specified temperature. See COOLANT TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS table. Replace sensor if not within specification.

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

COOLANT TEMP SENSOR RESISTANCE SPECIFICATIONS

EGR TEMPERATURE SENSOR

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

Impulse Turbo

See TIMING CONTROL SYSTEMS under IGNITION SYSTEMS.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

MAP sensor is located in left rear corner of engine compartment. To diagnose MAP sensor problem, see DIAGNOSTIC CHARTS, CHART C-1D, MAP SENSOR OUTPUT.

Note. A malfunctioning MAP sensor may set trouble Codes 33A and 33B. For additional sensor testing procedures, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

MANIFOLD AIR TEMPERATURE (MAT) SENSOR

1. Remove MAT sensor from intake manifold. MAT sensor is located near throttle position sensor and contains a Blue/Black and Black/White wire connector.
2. Using ohmmeter, check resistance across sensor terminals. Reading should vary with temperature. Replace sensor if not within specification. See MAT SENSOR RESISTANCE SPECIFICATIONS table.

Note. If a MAT sensor problem develops, ECM will set Code 23A or 23B. For additional testing procedures, see appropriate G - EFI TESTS W/ CODES article in the ENGINE PERFORMANCE Section.

MAT SENSOR RESISTANCE SPECIFICATIONS

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 78) 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 78

PARK/NEUTRAL SWITCH CONTINUITY SPECIFICATIONS

PARK/NEUTRAL SWITCH RELAY

For Park/Neutral switch relay testing procedure, see DIAGNOSTIC CHARTS, CHART C-1A, PARK/NEUTRAL SWITCH RELAY. Relay is mounted in relay box at right front corner of engine compartment.

POWER STEERING PRESSURE SWITCH

Power steering pressure switch is located in power steering pump housing. To test power steering pressure switch, see DIAGNOSTIC CHARTS, CHART C-1D, POWER STEERING PRESSURE SWITCH. Replace switch if defective.

THROTTLE POSITION SENSOR (TPS)

1. Unplug TPS harness at sensor. Connect ohmmeter between Blue/Red or Yellow/Blue and Black/White wire terminals of sensor
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 Impulse & Stylus (1) Behind Left Side Of Instrument Panel (1) DO NOT confuse transaxle Electronic Control Unit (ECU), located on left side of instrument panel, with ECM located behind air duct. ECM contains a 24-pin and 32-pin connector. Transaxle ECU contains a 16-pin and 20-pin connector.
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 terminal C14 (Blue/Orange 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 ECM wire terminal C13 (Yellow/Blue 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 21A or 21B 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.

VEHICLE SPEED SENSOR

1. With instrument cluster removed, use ohmmeter to check continuity across vehicle speed sensor (VSS) terminals. (Scheme 79)
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 79

Note. If a problem develops with vehicle speed sensor, ECM will set Code 24. For additional testing procedures, see 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 80) and (Scheme 81) as examples.

Scheme 80

Scheme 81

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 82

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.

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 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.

IDLE AIR CONTROL VALVE

1. If Idle Air Control (IAC) valve is operating improperly, remove IAC valve from throttle body. Inspect IAC valve and throttle body bore for binding and clogged passages. Repair as necessary. If binding or clogged passages is not present, proceed to step 2).
2. Disconnect electrical connector from IAC valve. Using ohmmeter, check resistance across terminals No. 1 and No. 2 and across terminals No. 3 and No. 4. (Scheme 83) Replace IAC valve if resistance is not 40-80 ohms.
3. Using ohmmeter, check continuity across terminals No. 1 and No. 4 and across terminals No. 2 and No. 3. Replace IAC valve if continuity exists.
4. If IAC valve tests okay, check for faulty connections at IAC valve and ECM. If connections are okay, check input devices used by ECM to control IAC valve operation.

Scheme 83

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 (ESC) (Impulse Turbo)

To test ESC system, see DIAGNOSTIC CHARTS, CHART C-5, ESC SYSTEM. ESC module is part of MEM-CAL.

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 (EST) (Impulse Non-Turbo & Stylus)

1. To check system operation, check timing at 1500 RPM with ALDL ungrounded. Locate ALDL connector.
2. ALDL is located behind right side of instrument panel. (Scheme 84)
3. Install jumper wire between terminals "A" and "C" of ALDL connector. (Scheme 84) 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 84

EXHAUST GAS RECIRCULATION (EGR)

Note. On Impulse and Stylus, EGR Vacuum Switching Valve (VSV) may also be referred to as EGR control solenoid.

EGR System

EGR vacuum switching valve (VSV) is located behind distributor on non-turbo models and in front of brake booster on turbo models. To check EGR system, see DIAGNOSTIC CHARTS, CHART C-7A, EGR SYSTEM.

EGR Transducer

1. Remove vacuum hoses from EGR transducer. Place finger over port "P", and blow into port "Q". (Scheme 85)or (Scheme 86). Air should pass through filter of EGR transducer.
2. Place finger over port "P", and blow into port "R". Air should pass through EGR transducer, but be restricted. Replace EGR transducer if defective.

Scheme 85

Scheme 86

Note. On Impulse and Stylus, EGR vacuum switching valve (VSV) may also be referred to as EGR control solenoid.

EGR Vacuum Switching Valve (VSV)

1. Disconnect vacuum hoses from VSV, located behind distributor. With ignition off, disconnect electrical connector from VSV.
2. Using ohmmeter, check resistance between VSV terminals. Replace VSV if resistance is not 33-39 ohms. If resistance is okay, blow air into port "A". (Scheme 85)or (Scheme 86). Air should pass through air filter and not through port "B". Replace assembly if air passes through port "B".
3. Install electrical connector on VSV. Turn ignition on. Install jumper wire between terminals "A" and "C" of ALDL. (Scheme 84) ALDL is located behind right side of instrument panel.
4. Blow air into port "A". Air should pass from port "B". If air does not pass from port, check wiring between ECM and VSV. If wiring is okay, replace VSV.

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.

Canister Purge Control Valve (Impulse Non-Turbo & Stylus)

1. Purge control valve is an integral part of canister. With engine running, vacuum signal is supplied to top hose of purge control valve. Purge control valve opens at 15 in. Hg, allowing vapors to purge from canister into intake manifold through purge control valve lower hose.
2. Connect vacuum hose to lower hose connection of purge control valve, and attempt to blow through it. Little or no air should pass through purge control valve into canister.
3. Using hand-held vacuum pump, apply 15 in. Hg to upper hose connection of purge control valve. Again attempt to blow through lower hose. Air should pass easily into cansiter. If air does not pass easily, replace canister and purge control valve as an assembly.

Canister Purge Solenoid Valve (Impulse Turbo)

For diagnosis of canister purge solenoid valve, see DIAGNOSTIC CHARTS, CHART C-3, CANISTER PURGE SOLENOID VALVE DIAGNOSIS.

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.

MISCELLANEOUS CONTROLS

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

A/C CLUTCH CONTROL

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

CHART C-1A, PARK/NEUTRAL SWITCH RELAY

Park/Neutral switch contacts are closed to ground in Park or Neutral and open in all other ranges. ECM supplies voltage through a resistor on Pink/Blue wire from ECM to relay. ECM senses when switch is closed and voltage decreases to less than one volt on Pink/Blue wire. ECM uses this input to control idle speed, EGR operation and vehicle speed sensor diagnostics.

If Pink/Blue wire indicates Park or Neutral (grounded) while in Drive range, EGR will not operate, resulting in possible detonation. If Pink/Blue wire indicates Drive (open), a decrease in idle speed may occur when gearshift is placed in gear.

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

1. This step checks for a closed switch to ground in Park position.
2. This step checks for an open switch in Drive range.
3. Ensure Scan tester indicates Drive even while slightly moving gearshift. This will check for an intermittent or misadjusted switch in Drive or Overdrive range.

Scheme 87

Scheme 88

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 1.2-2.3 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)

Scheme 89

Scheme 90

CHART C-1D, POWER STEERING PRESSURE SWITCH

Power Steering Pressure Switch (PSPS) is normally open and circuit No. 901 is approximately battery voltage. When power steering pump pressure increases, PSPS closes, causing voltage on circuit No. 901 to fall to less than one volt.

ECM monitors voltage and increases idle speed when voltage decreases. If PSPS fails to close or open exists in circuit No. 901, engine may stall when power steering pump pressure is high. If PSPS fails to open or short to ground exists in circuit No. 901, idle speed may be affected and A/C relay will be de-energized.

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

1. Check Scan tester instructions on how switch state will be displayed.
2. This step checks for a short to ground in circuit No. 901
3. This step simulates a closed switch.

Scheme 91

Scheme 92

CHART C-2D, SECONDARY AIR SYSTEM

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

1. Without proper vacuum at solenoid, system will not function properly.
2. When ignition is on and engine is not running, solenoid should not be energized. Solenoid is normally closed, vacuum should not pass to actuator.
3. With diagnostic terminal grounded, ECM should ground circuit No. 476 on Impulse (non-turbo) and Stylus. On Impulse (turbo), White/Blue wire circuit should be grounded. ECM terminal for Impulse (non-turbo) and Stylus is M2-2. ECM terminal for Impulse (turbo) is A4. When these circuits are grounded, solenoid will energize, allowing vacuum to pass to actuator.
4. This step checks vacuum actuators ability to move secondary intake valve linkage.
5. This step checks circuit continuity.

Scheme 93

Scheme 94

CHART C-3, CANISTER PURGE SOLENOID VALVE (IMPULSE TURBO)

Canister purge is controlled by a solenoid which allows manifold and/or ported vacuum to purge canister when energized. ECM supplies ground to energize solenoid (purge on).

Purge solenoid is turned on under following conditions

1. ALDL is not grounded.
2. Engine has been running for longer than 20 seconds.
3. Coolant temperature is greater than 140°F (60°C).
4. Vehicle speed is less than 15 MPH.
5. Solenoid is also energized when diagnostic test terminal (ALDL) is grounded with engine off.

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

1. Checks to see if solenoid is open or closed. Solenoid is normally de-energized in this step, so it should be closed.
2. Checks if solenoid was open due to electrical circuit problem or defective solenoid.
3. Completes functional check by grounding test terminal. This should normally energize solenoid, which should open valve and allow vacuum to drop and purge canister.

Diagnostic Aids

Visually check vacuum hoses. Check throttle body for possible cracked and plugged vacuum hoses. Check engine for possible mechanical problem.

Scheme 95

Scheme 96

CHART C-5, ESC SYSTEM (IMPULSE TURBO)

Knock sensor is used to detect engine detonation and ECM will retard electronic spark timing based on signal being received. Circuitry within knock sensor pulls 5-volt signal from ECM down to approximately 2.5 volts DC. Knock sensor produces an AC signal which rides back to ECM on 2.5 volts DC voltage. Amplitude and frequency are dependent upon knock level.

MEM-CAL used with this engine contains functions which were part of remotely mounted ESC modules used on other vehicles. ESC portion of MEM-CAL then sends signal to other parts of ECM which adjusts spark timing to retard spark and reduce detonation.

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

1. With engine idling, knock signal should not be present at ECM because detonation is not likely under a no-load condition.
2. Tapping on engine lift bracket should simulate a knock signal to determine if sensor is capable of detecting detonation. If no knock is detected, try tapping on engine block closer to sensor before replacing sensor.
3. If engine has an internal problem which is creating a knock, knock sensor may be responding to internal failure.
4. This test determines if knock sensor is faulty or if ESC portion of MEM-CAL is faulty. If it is determined MEM-CAL is faulty, ensure it is properly installed and latched into place. If not properly installed, repair and retest.

While observing knock signal on Scan tester, an indication knock is present when detonation can be heard should exist. Detonation is most likely to occur under high engine load conditions.

Scheme 97

Scheme 98

CHART C-7A, EGR SYSTEM (IMPULSE NON-TURBO & STYLUS)

ECM operates a Vacuum Switching Valve (VSV) to control vacuum to EGR valve. This solenoid is normally closed. ECM provides a ground to solenoid and VSV opens, allowing vacuum to EGR valve.

Engine control system operates within 2 block learn cells, a closed throttle cell and a open throttle cell. Open throttle cell is affected by EGR operation. When EGR system is operating correctly, block learn in both cells should be approximately the same. If EGR system is inoperative, open throttle block learn value would increase, but block learn value at closed throttle would not change. This change or difference in block learn values is used to monitor EGR operation.

If EGR system works properly, check for restricted EGR passages or defective MAP sensor. These items could cause high block learn values in open throttle, but not in closed throttle.

Scheme 99

CHART C-7A, EGR SYSTEM (IMPULSE TURBO)

ECM operates a Vacuum Switching Valve (VSV) to control vacuum to EGR valve. This solenoid is normally closed. ECM provides a ground to solenoid and VSV opens, allowing vacuum to EGR valve.

Engine control system operates within 2 block learn cells, a closed throttle cell and a open throttle cell. Open throttle cell is affected by EGR operation. When EGR system is operating correctly, block learn in both cells should be approximately the same. If EGR system is inoperative, block learn value at open throttle would increase, but block learn value at closed throttle would not change. This change or difference in block learn values is used to monitor EGR operation.

If EGR system works properly, check for restricted EGR passages or defective MAP sensor. These items could cause high block learn values in open throttle, but not in closed throttle.

Scheme 100

CHART C-10, A/C CLUTCH CONTROL DIAGNOSIS (IMPULSE TURBO)

When A/C mode is selected, ECM supplies a ground to A/C clutch relay. Battery voltage is then supplied to A/C clutch through completion of circuit through thermoswitch relay. If A/C system exhibits high pressure or an overheating conditions exists, A/C system will be disabled by opening of A/C high pressure switch or A/C thermoswitch.

A/C high pressure switch is located in high pressure side of A/C hose. Thermo cut-out switch is part of A/C evaporator mounted under dash.

Scheme 101