Engine Controls - Tests W/o Codes Mazda 929 HD

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in appropriate BASIC TESTING article and appropriate TESTS W/CODES article in BASIC TESTING TABLE and G -TESTS W/ CODES TABLE. Use this article to diagnose driveability problems existing when a hard fault code is not present or vehicle is not equipped with a self-diagnostic system.

F - BASIC TESTING

G - TESTS W/ CODES

Note. Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or computer application.

Symptom checks can direct the technician to malfunctioning components for further diagnosis. A symptom should lead to a specific component, system test or adjustment.

Use intermittent test procedures to locate driveability problems that do not occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present but no problem was found during self-diagnostic testing.

Note. For specific testing procedures, see appropriate article in I - SYS/COMP TESTS TABLE below. For specifications, see appropriate article in D - ADJUSTMENTS TABLE or C - SPECIFICATIONS TABLE below.

I - SYS/COMP TESTS

D - ADJUSTMENTS

C- SPECIFICATIONS

SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate BASIC TESTING article and appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section were performed before diagnosing a symptom. See BASIC TESTING and TESTS W/CODES TABLE in this article. Following symptoms are available for diagnosis.

1. Difficult To Start Or Will Not Start
2. Rough Or Unstable Idle
3. High Idle After Warm Up
4. Engine Stalls
5. Engine Misfires Or Has Lack Of Power
6. Engine Runs Rough On Deceleration
7. Backfire In Exhaust System
8. Poor Fuel Mileage
9. Excessive Oil Consumption
10. Abnormal Noise Or Knocking

DIFFICULT TO START OR WILL NOT START

1. Check battery condition.
2. Check condition of spark plugs.
3. Ensure fuel system pressure is correct.
4. Check Electronic Fuel Injection (EFI) main fuse located in fuse box (if equipped).
5. Ensure inertia switch circuit is not open (Navajo).
6. Verify crank angle sensor has correct resistance values (B2300, B4000, MX-3 1.8L, MX-6 and 626 2.5L, Navajo, RX7 and 929).
7. Verify optical sensor is working (Miata, Protege and 323).
8. Check coolant temperature sensor resistance.
9. Verify Hall-Effect sensor is working (MX-3, MX-6, 626 and 929).
10. Check for leaky fuel injectors or pressure regulator causing warm-engine no start.
11. Check fuel pump relay operation. A click should be heard from relay as ignition switch is cycled on and off.
12. Check distributor pick-up coil resistance (if equipped).
13. Ensure pressure regulator control system is okay.
14. Check air intake system for restriction.
15. Check EGR valve and solenoid for correct operation.
16. Check for cracks and poor connections at airflow meter or throttle body.
17. Check ignition coil resistance.

ROUGH OR UNSTABLE IDLE

1. Use stethoscope to verify fuel injector operating noise.
2. Ensure fuel system pressure is correct.
3. Check EGR valve condition and operation.
4. Verify ignition timing is correct.
5. Check PCV valve.
6. Check airflow sensor.
7. Check coolant thermosensor for correct resistance.
8. Check idle air control valve function.
9. Check for cracks and poor connections (vacuum leaks) at airflow meter or throttle body.
10. Check O2 sensor for fluctuating 0.1-1.0 volt output while increasing and decreasing engine RPM.
11. Verify throttle position sensor has correct adjustment and resistance value.
12. Check purge valve function.
13. Check for poor fuel quality.

HIGH IDLE AFTER WARM UP

1. Verify correct throttle body dashpot adjustment (if equipped).
2. Check idle air control valve and ISC valve operation.
3. Check air intake system for leaks or restriction.
4. Check throttle cable adjustment.
5. Check coolant temperature sensor resistance.
6. Ensure fuel system pressure is correct.
7. Check airflow meter for cracks. Verify correct airflow meter operation and resistance value.
8. Check ignition timing.

Cold

1. Ensure air filter element is clean.
2. Check fuel filter for restriction.
3. Check EGR valve condition and operation.
4. Check for airflow meter or ISC valve malfunction.
5. Ensure fuel system pressure is correct.
6. Check air intake system for vacuum leaks.
7. Check coolant temperature sensor resistance.
8. Verify correct throttle position sensor adjustment and resistance value.
9. Check neutral switch (M/T) or inhibitor switch (A/T).

Warm

1. Check PCV system for restrictions.
2. Check air valve or ISC valve for malfunction.
3. Check connections at airflow meter or throttle body.
4. Check operation of lock-up torque converter.
5. Check coolant temperature sensor resistance.
6. Ensure fuel system pressure is correct. Use ohmmeter to verify correct fuel injector resistance.
7. Check throttle bore for dirt and carbon.

ENGINE MISFIRES OR HAS LACK OF POWER

1. Verify air filter is clean.
2. Check fuel filter for restriction.
3. Check vacuum switching valve operation.
4. Check coil resistance.
5. Check airflow meter for cracks.
6. Check EGR valve and solenoid for correct operation (if equipped).
7. Check purge control valve operation.
8. Check airflow operation and resistance value.
9. Check atmospheric pressure sensor.
10. Check ignition system for intermittent operation.
11. Check for restricted catalytic converter.
12. Check Variable Resonance Induction System (VRIS) for correct operation (if equipped).
13. Check Variable Inertia Charge System (VICS) for correct operation (if equipped).
14. Verify crank angle sensor (permanent magnet type) has correct resistance values.
15. Check A/C cut-off system (if equipped).
16. Ensure fuel system pressure is correct.
17. Check turbocharger system (if equipped) for wear or malfunctioning parts. Turbo system inspection should include the following: Turbo Precontrol Wastegate Control Turbo Control Charge Control Charge Relief

ENGINE RUNS ROUGH ON DECELERATION

1. Verify idle speed is correct.
2. Verify correct throttle body dashpot adjustment.
3. Check coolant thermosensor and throttle position sensor.
4. Check air valve or ISC valve for malfunction.
5. Check fuel pressure regulator.
6. Check O2 sensor operation.
7. Check throttle position sensor.
8. Check airflow sensor operation.

BACKFIRE IN EXHAUST SYSTEM

1. Verify base timing is correct and advance system is functional.
2. Ensure air filter element is clean.
3. Check throttle body dashpot adjustment (if equipped).
4. Check coolant temperature sensor and throttle position sensor.
5. Check air valve, ISC switch and idle switch operation.
6. Check intake air system and throttle body electrical connections for vacuum leaks.
7. Ensure fuel system pressure is correct.
8. Verify no leaks exist in exhaust system.

POOR FUEL MILEAGE

1. Check injectors for leakage.
2. Verify correct throttle body dashpot adjustment.
3. Ensure correct throttle position sensor adjustment and resistance value.
4. Check intake air and coolant temperature sensor.
5. Ensure fuel system pressure is correct.
6. Ensure exhaust system is unrestricted.

EXCESSIVE OIL CONSUMPTION

1. Check for restricted PCV system.
2. Check turbo system for malfunction.
3. Check metering oil pump (RX7).
4. Check for worn engine parts.

ABNORMAL NOISE OR KNOCKING

1. Check engine oil and coolant level.
2. Check turbo system (if equipped) for damage and wear.
3. Check engine control system for malfunctioning components.

System inspection should include following components

1. Airflow Meter
2. Idle Switch
3. Vacuum Routing (For Leaks)
4. Neutral Safety Switch (A/T)
5. Clutch Switch (M/T)
6. EGR Valve Position Sensor (If Equipped)
7. Knock Sensor (If Equipped)
8. Throttle Position Sensor
9. Coolant Temperature Sensor
10. Coolant Thermoswitch
11. Inhibitor Switch (A/T)
12. Electronic Controlled Automatic Transmission (ECAT) Unit

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify problem. These procedures may lead to computer setting a fault code (on some systems) which may help in diagnosis.

If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.

Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.

Intermittent Simulation

To reproduce conditions creating an intermittent fault, use the following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.

See also:
• BASIC TESTING
• SYSTEM/COMPONENT TESTS
• ADJUSTMENTS
• SPECIFICATIONS
• SYS/COMP TESTS TABLE