Engine Controls - System/component Tests Mazda 929 HD

INTRODUCTION

Before testing separate components or systems, perform procedures in 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 TESTS W/CODES article in the ENGINE PERFORMANCE section.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests using 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.

System Check

Start engine, and operate it at idle. Ensure shutter valve actuator rod is retracted at idle. (Scheme 29) Actuator rod should extend when engine is started, for 5 seconds after engine is started and when engine is operating at 1100-4800 RPM with throttle opened in "D" range. If necessary, check Variable Inertia Charging System (VICS) components.

Scheme 29

Check Valve

Remove check valve. Blow air through port "A", and verify flow through port "B". Ensure air does not flow in reverse direction. Replace as necessary.

Solenoid Valve

Remove solenoid valve. Blow air through port "B". (Scheme 30) Ensure air flows from valve air filter. Connect 12 volts and a ground to solenoid valve terminals. Blow air through valve port "B", and ensure air flows from port "A". Replace solenoid valve as necessary.

Scheme 30

Shutter Valve Actuator

Disconnect vacuum hose from shutter valve actuator. (Scheme 29) Connect vacuum pump to actuator. Apply vacuum and verify shutter valve rod retracts. Replace as necessary.

Shutter Valve

Shutter valve stopper bolt is preset at factory. DO NOT adjust shutter valve stopper bolt. Remove shutter valve actuator. Ensure shutter valve rotates smoothly. (Scheme 31) Replace dynamic chamber if valve is stuck or does not rotate smoothly.

Scheme 31

Vacuum Chamber

Remove vacuum chamber. Visually inspect vacuum chamber for clogging, cracks and damage. Replace as necessary.

Remove check valve. Blow air through port "A" and verify flow through port "B". Ensure air does not flow in reverse direction. Replace as necessary.

POWERTRAIN CONTROL MODULE

1. Locate Electronic Control Unit (ECU) or Powertrain Control Module (PCME). See ECU/PCME LOCATION table. Connect Engine Signal Monitor (49-9200-162) to ECU/PCME. (Scheme 32) Check voltage at each terminal of ECU/PCME. If input and output component voltage readings are not as specified, check faulty component. Proceed to «PIN VOLTAGE CHARTS»(/mazda/929/hd-1993-1995/remont/pin-voltage-charts/#engine-controls-pin-voltage-charts) article in the ENGINE PERFORMANCE section, «TESTS W/CODES»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-tests-wcodes) article, and testing for appropriate component in this article.
2. If input and output component voltages are as specified and ECU/PCME voltage is incorrect, replace ECU/PCME.

ECU/PCME LOCATION

Scheme 32

A/C SWITCH

See A/C CUT-OFF CONTROL SYSTEM under A/C CLUTCH under MISCELLANEOUS CONTROLS.

AIRFLOW METER

Inspect airflow meter for damage, and ensure measuring plate or cone moves smoothly. (Scheme 33) Disconnect airflow meter electrical connector. Move measuring plate or cone, and measure resistance between terminals. See appropriate AIRFLOW METER TERMINAL RESISTANCE table. Replace sensor as necessary.

AIRFLOW METER TERMINAL RESISTANCE

Scheme 33

ATMOSPHERIC PRESSURE SENSOR

See PIN VOLTAGE CHARTS article in the ENGINE PERFORMANCE section.

BRAKELIGHT SWITCH

Disconnect brakelight switch connector. Measure resistance between terminals of brakelight switch. With brake pedal released, continuity should not exist. With brake pedal depressed, continuity should be present. Replace switch as necessary.

CENTRAL PROCESSING UNIT (CPU)

CPU acts as an electrical load sensor. Remove CPU from behind left front side trim panel near door. (Scheme 34)-10. Check voltage at terminals of CPU connector. See appropriate CPU UNIT VOLTAGE CHART. If voltages are incorrect, check appropriate circuit. If circuits are okay but voltages are still incorrect, replace CPU.

Scheme 34

Scheme 35

Scheme 36

Scheme 37

Scheme 38

CLUTCH SWITCH (M/T)

Disconnect clutch switch electrical connector. Using ohmmeter, check continuity between switch terminals. With clutch pedal depressed, continuity should be present. With clutch pedal released, continuity should not exist. Replace switch as necessary.

COLD START THERMOSWITCH

Remove cold start thermoswitch. Place thermoswitch and thermometer in container of coolant. Connect ohmmeter to thermoswitch terminals. Slowly heat coolant. Note resistance at specified temperatures. See COLD START THERMOSWITCH RESISTANCE table. Replace thermoswitch as necessary.

COLD START THERMOSWITCH RESISTANCE

CRANK ANGLE SENSOR

See IGNITION CHECKS in BASIC TESTING article in the ENGINE PERFORMANCE section.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

Remove engine coolant temperature sensor. Place sensor and thermometer in container of coolant. Connect ohmmeter to sensor terminals. Slowly heat coolant. Note resistance at specified temperatures. See appropriate ECT SENSOR RESISTANCE table. Replace sensor as necessary.

ECT SENSOR RESISTANCE

EGR POSITION SENSOR

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

HEATED OXYGEN SENSOR (HO2S)

With engine at room temperature, disconnect HO2S connector. Measure resistance across terminals "C" and "D". (Scheme 39) See HO2S RESISTANCE table. Replace HO2S as necessary. Also se PIN VOLTAGE CHARTS article in the ENGINE PERFORMANCE section.

HO2S RESISTANCE

Scheme 39

IDLE SWITCH

Idle switch is part of throttle position sensor. See ADJUSTMENTS article in the ENGINE PERFORMANCE section.

Scheme 40

INHIBITOR SWITCH (A/T)

Disconnect inhibitor switch electrical connector. Connect ohmmeter to indicated switch terminals. (Scheme 41) Continuity should be present with gearshift in Park and Neutral positions. Continuity should not exist in any other gear positions. Replace switch as necessary.

Scheme 41

INTAKE AIR THERMOSENSOR (DYNAMIC CHAMBER)

Remove intake air thermosensor. Using a heat light, ohmmeter and thermometer, measure resistance of sensor at various temperatures. (Scheme 42) See INTAKE AIR THERMOSENSOR RESISTANCE table. Replace sensor as necessary.

INTAKE AIR THERMOSENSOR RESISTANCE

Scheme 42

KNOCK SENSOR

See PIN VOLTAGE CHARTS article in the ENGINE PERFORMANCE section.

OXYGEN (O2S) SENSOR

1. Warm engine to operating temperature. Operate engine at idle. Disconnect O2S sensor electrical connector. Connect voltmeter between O2S sensor connector terminals "A" and "B". (Scheme 43)
2. Observe voltmeter while rapidly accelerating and decelerating engine speed. Voltage should be 0.5-1.0 volt during acceleration and 0.0-0.4 volt during deceleration. Replace O2S sensor as necessary.

Scheme 43

POWER STEERING PRESSURE SWITCH (PSPS)

Disconnect power steering pressure switch electrical connector. Connect ohmmeter to PSPS terminals. Start engine, and operate it at idle. Turn steering wheel from side to side, and observe ohmmeter. Ohmmeter should indicate continuity when front wheels are turned. Continuity should not exist when wheels are not turned. Replace switch as necessary.

THROTTLE POSITION SENSOR

See ADJUSTMENTS article in the ENGINE PERFORMANCE section for checking and adjustment procedures.

VEHICLE SPEED SENSOR (VSS)

See PIN VOLTAGE CHARTS article in the ENGINE PERFORMANCE section.

1. Connect positive lead of voltmeter to Green/Red wire of combination meter. Connect negative lead of voltmeter to ground. Raise and support rear wheels. Start engine. Engage Drive and rotate rear wheels. Voltmeter should show 3-4 volts. If not, stop engine.
2. Disconnect connector from combination meter. Measure resistance across Blue/White and Blue/Yellow wires (terminals 1K and 1L). Resistance should be 290 ohms. If resistance is not 290 ohms, check wiring to transmission. If wiring is okay, check resistance of VSS at transmission.
3. If resistance of VSS is not 290 ohms, replace VSS. If resistance of VSS is 290 ohms, replace VSS buffer in instrument cluster.

Circuit Opening Relay

See FUEL PRESSURE under FUEL SYSTEM in BASIC TESTING article in the ENGINE PERFORMANCE section.

Cold Start Injector Relay

Remove cold start injector relay. Apply battery voltage to terminal "C", and ground terminal "D". Continuity should be present with battery voltage applied. Continuity should not exist without voltage applied. Replace relay as necessary.

Main Relay

1. Ensure main relay clicks when ignition is turned on and off.
2. If no sound is heard, unplug relay. Apply 12 volts to terminal "A", and ground terminal "B". (Scheme 43)
3. Using ohmmeter, check continuity between terminals "C" and "D". Continuity should be present with 12 volts applied. Continuity should not exist with no voltage applied. Replace main relay as necessary.

Scheme 44

Cold Start Injector Resistance

Disconnect cold start injector electrical connector. Using ohmmeter, measure resistance between injector terminals. Resistance should be 2.7-3.4 ohms at 68°F (20°C). Replace injector as necessary.

EGR Solenoid

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

Fuel Injectors

Using stethoscope, listen for normal clicking sound at each injector during idle and acceleration. If clicking sound is not heard, check injector wiring circuit, or main relay and circuit.

Fuel Injector Resistance

Disconnect fuel injector electrical connector. Using ohmmeter, measure resistance between injector terminals. Resistance should be 12-16 ohms. Replace injector as necessary.

Pressure Regulator Control Solenoid

Disconnect vacuum hose from pressure regulator control solenoid. Blow air through solenoid port "A". (Scheme 45) Ensure air flows through port "B". Disconnect solenoid valve electrical connector. Connect 12 volts and ground to solenoid terminals. Blow air through solenoid port "A". Air should flow through valve air filter. Replace solenoid as necessary.

Scheme 45

Purge Control Solenoid

See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS.

VICS Solenoid

See VARIABLE INERTIA CHARGING SYSTEM under AIR INDUCTION SYSTEMS.

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING article in the ENGINE PERFORMANCE section.

See FUEL PRESSURE under FUEL SYSTEM in BASIC TESTING article in the ENGINE PERFORMANCE section.

Fuel Pump Circuit

See FUEL PRESSURE under FUEL SYSTEM in BASIC TESTING article in the ENGINE PERFORMANCE section.

Fuel Pressure Regulator

See FUEL PRESSURE under FUEL SYSTEM in BASIC TESTING article in the ENGINE PERFORMANCE section.

See PRESSURE REGULATOR CONTROL SOLENOID under SOLENOIDS under RELAYS & SOLENOIDS.

See FUEL INJECTORS under SOLENOIDS under RELAYS & SOLENOIDS.

Injector Fuel Leakage

1. Relieve fuel system pressure. See «BASIC TESTING»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-basic-testing) article in the ENGINE PERFORMANCE section. Remove air valve or dynamic chamber as necessary. Remove delivery pipe with hoses still connected. Remove fuel injectors. Using wire, secure injectors tightly onto delivery pipe. CAUTION: Ensure injectors are securely tied to delivery pipe. If injectors are not properly secured to delivery pipe, fuel may spray from loose connections.
2. Connect a jumper wire between terminals F/P and GND of diagnostic connector located near battery. (Scheme 46)
3. Turn ignition on for 10 seconds. Turn ignition off, and clean injector nozzles. Turn ignition on. Ensure no fuel leakage exists at injectors. After one minute, a single drop of fuel is acceptable. If fuel leakage is present, replace faulty injector.

Scheme 46

Air Valve

1. Disconnect air hoses from air valve. Blow air through valve from port "A" and ensure air flows through valve when engine is cold. (Scheme 47)
2. Warm engine to normal operating temperature. Blow air through valve from port "A". Air should not flow through valve. Replace valve as necessary.

ISC Valve

Disconnect ISC valve electrical connector. Connect ohmmeter to ISC valve 2-wire connector. Measure resistance. See ISC RESISTANCE SPECIFICATIONS table. If resistance is not within specification, replace ISC valve.

Scheme 47

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC TESTING article in the ENGINE PERFORMANCE section.

DECELERATION CONTROL SYSTEM

Note. Deceleration control system is a function of dashpot and ECU. Dashpot prevents sudden closure of throttle valve. ECU controls fuel cut during deceleration. For adjustment and testing, see ADJUSTMENTS article in the ENGINE PERFORMANCE section.

1. Connect Engine Signal Monitor (49-9200-162) and Test Harness (49 G018 903) to ECU. Start engine. Increase engine speed, and check voltage at ECU terminals 3O and 3P while engine is cold. See «PIN VOLTAGE CHARTS»(/mazda/929/hd-1993-1995/remont/pin-voltage-charts/#engine-controls-pin-voltage-charts) article in the ENGINE PERFORMANCE section. Voltage should be 12 volts.
2. Warm engine to operating temperature, and operate it at idle. Increase engine speed, and ensure engine signal monitor Green and Red lights flash at ECU terminals 3O and 3P.
3. Disconnect EGR solenoid valve (vacuum side) electrical connector. Apply 12 volts and a ground to solenoid valve. Ensure engine runs rough or stalls at idle. Test EGR components as necessary. (Scheme 48)

Scheme 48

EGR Control Valve

Bring engine to normal operating temperature and operate at idle. Disconnect and plug vacuum hose at EGR control valve. Engine should run smoothly. Connect vacuum pump to EGR control valve, and apply vacuum. See EGR CONTROL VALVE OPERATING VACUUM table. Engine should run rough or stall. If engine does not operate as specified, clean or replace EGR control valve.

EGR CONTROL VALVE OPERATING VACUUM

1. Disconnect EGR position sensor electrical connector. Connect ohmmeter to EGR position sensor. Disconnect vacuum hose from EGR control valve. Apply vacuum to EGR control valve.
2. Check sensor resistance between indicated terminals. See «EGR POSITION SENSOR RESISTANCE»(/mazda/929/hd-1993-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. If resistance is not within specifications, replace sensor.

EGR POSITION SENSOR VOLTAGE

EGR POSITION SENSOR RESISTANCE

EGR Solenoid Valve

1. Disconnect vacuum hoses. Blow air through vacuum hose (vacuum side). Ensure air does not flow. Disconnect EGR solenoid valve (vacuum side) electrical connector. Apply 12 volts and a ground to solenoid valve (vacuum side) terminals. (Scheme 49) Blow air through vacuum hose and ensure air flows.
2. Blow air through vacuum hose (vent side). Ensure air flows. Disconnect EGR solenoid valve (vent side) electrical connector. Apply 12 volts and a ground to solenoid valve (vent side) terminals. (Scheme 49) Blow air through vacuum hose and ensure air does not flow. Replace solenoid valves as necessary.

Scheme 49

System Inspection

Purge system operation takes place when vehicle is accelerating in gear (off idle), engine is at operating temperature and oxygen sensor is functioning normally. (Scheme 50)

Scheme 50

Charcoal Canister

Check for loose, missing, cracked and broken connections and parts. Repair or replace as necessary. No liquid should exist in canister.

2-Way Check Valve

Remove check valve. Connect a vacuum pump to one end of check valve. Air should flow with about 1-1.7 in. Hg applied. Connect vacuum pump to other end of check valve. Air should also flow with about 1-1.7 in. Hg applied. Replace valve as necessary.

3-Port Check Valve

Note direction of valve installation. Remove check valve. Cap port going to 2-way check valve. Connect a vacuum pump to lower port. Air should flow from port going to fuel tank with 3.0 in. Hg applied. Replace valve as necessary.

Fuel Vapor Valve

Remove fuel vapor valve. Blow air into upper port of valve. Air should flow through valve to lower port. Turn valve upside down. Blow air through lower port of valve. Air should not flow. Replace valve as necessary.

Purge Control Solenoid Valve

1. Warm engine to normal operating temperature and operate at idle. Disconnect vacuum hoses from solenoid valve. Ensure vacuum is not present at solenoid valve. Disconnect vacuum hoses from charcoal canister.
2. Ensure air does not flow through solenoid valve. If air flows through solenoid valve, disconnect solenoid valve connector. Connect 12 volts and a ground to solenoid valve terminals. (Scheme 51) Blow air through check valve. Air should flow through valve. Replace valve as necessary.

Separator

Check for loose, missing, cracked and broken connections and parts. Repair or replace as necessary. No liquid should exist in canister.

Scheme 51

1. Warm engine to normal operating temperature, and operate it at idle. Disconnect Positive Crankcase Ventilation (PCV) valve, together with vent hose, from valve cover. Block PCV valve opening and check for vacuum. If no vacuum is felt, check for collapsed line and blockage.
2. Note direction of valve installation. Remove PCV valve. Blow air into upper port of valve. Air should flow through valve from lower port. Blow air through lower port of valve. Air should not flow from upper port. Replace valve as necessary.

A/C Cut-Off Control System

1. Turn A/C, blower and ignition on. DO NOT start engine. Shift transmission into a drive gear. Open throttle fully. Listen for A/C clutch disengaging and re-engaging after a few seconds. See A/C CUT-OFF TIME SPECIFICATIONS table.
2. If system does not function as specified, check operation of related switches, sensors and relays. See «PIN VOLTAGE CHARTS»(/mazda/929/hd-1993-1995/remont/pin-voltage-charts/#engine-controls-pin-voltage-charts) article in the ENGINE PERFORMANCE section.

A/C CUT-OFF TIME SPECIFICATIONS

See also:
• BASIC TESTING
• TESTS W/CODES
• PIN VOLTAGE CHARTS
• ADJUSTMENTS
• A/C CLUTCH