Engine Controls - Tests W/o Codes: Other Mazda 626 GD

DIFFICULT OR NO START (CRANKS OKAY) (CARB)

1. Check battery condition.
2. Ensure sufficient secondary spark is available.
3. Verify choke valve is closed (engine cold).
4. Verify choke valve is open (engine hot).
5. Ensure fuel level is at specified mark on carburetor sight glass.
6. Ensure fuel system pressure is correct.
7. Check mixture control valve operation.
8. Check for correct vacuum hose routing.
9. Check slow fuel-cut solenoid valve operation. A click should be heard from solenoid valve as ignition switch is cycled on and off.
10. Check duty solenoid valve for correct switching.
11. Check charcoal canister operation by clamping hose(s) shut. If problem goes away, check vacuum hose routing. If routing is correct, replace charcoal canister.
12. Ensure winter grade fuel is not being used in warm climate conditions.
13. Ensure exhaust system is not restricted.

DIFFICULT OR NO START (CRANKS OKAY) (EFI)

1. Check battery condition.
2. Check Electronic Gasoline Injection (EGI) main fuse located in fuse box (if equipped).
3. Verify crank angle sensor at connector has correct resistance values (RX7 models only).
4. Check main relay operation. A click should be heard from main relay as ignition switch is cycled on and off.
5. Verify distributor connector parallel terminal resistance is correct.
6. Ensure distributor pick-up coil resistance is correct.
7. Ensure pressure regulator control system is okay.
8. Ensure secondary air injection system is functioning correctly (if equipped).
9. Check air intake system for restriction.
10. Check EGR valve and solenoid for correct operation.
11. Check for cracks or poor connections at airflow meter or throttle body.
12. Ensure ignition coil has correct resistance.

ROUGH OR UNSTABLE IDLE (CARB)

1. Ensure there are no vacuum leaks.
2. Verify vacuum hose routing is correct.
3. Ensure fuel level is at specified mark on carburetor sight glass.
4. Check PCV operation by clamping hose shut. If problem goes away, replace PCV valve.
5. Check EGR operation.
6. Verify ignition timing is correct.
7. Briefly remove spark plug wires individually to determine if problem can be isolated.
8. Verify mixture control solenoid operation is correct.

ROUGH OR UNSTABLE IDLE (EFI)

1. Use sound amplification tool to verify operational noise coming from fuel injector(s).
2. Ensure fuel system pressure is correct.
3. Check PCV system for restrictions.
4. Check coolant thermosensor for correct resistance.
5. Check air valve or ISC valve for malfunction.
6. Check for cracks or poor connections at airflow meter or throttle body.
7. Check O2 sensor for 0-1.0 volt output while increasing and decreasing engine RPM.
8. Verify throttle position sensor has correct adjustment and resistance value.
9. Check for purge valve malfunction.

EXCESSIVE FAST IDLE (CARB)

1. Ensure no vacuum leaks present.
2. Check choke adjustment and operation.
3. Check throttle cable adjustment.
4. Check ignition timing.
5. Verify dashpot disengages throttle lever at 1900-2100 RPM.

EXCESSIVE FAST IDLE (EFI)

1. Verify correct throttle body dashpot adjustment.
2. Check By-Pass Air Control (BAC) valve and ISC valve operation.
3. Check air intake system for leaks or restriction.
4. Check pressure regulator control system.
5. Ensure fuel system pressure is correct.
6. Check coolant thermosensor.
7. Check airflow meter for cracks. Verify correct airflow operation and resistance value.

Carbureted Models

1. Verify correct air cleaner intake control door operation.
2. Ensure correct choke adjustment and operation.
3. Check choke diaphragm vacuum source.
4. Check choke diaphragm for damage.
5. Check idle mixture adjustment.
6. Ensure there are no vacuum leaks.
7. Check PCV operation by clamping hose shut. If problem goes away, replace PCV valve.
8. Check A/C cut-off system.
9. Check HAC valve operation.
10. Check EGR valve operation.

Cold

1. Ensure air intake system is unrestricted.
2. Remove By-Pass Air Control (BAC) valve hose and check valve for restrictions. If no restrictions are found, check resistance at BAC valve terminals.
3. Check EGR valve and solenoid for correct operation.
4. Check intake air and water thermosensor.
5. Check airflow meter or ISC valve malfunction.
6. Check A/C cut-off system.
7. Ensure fuel system pressure is correct.
8. Check for cracks or poor connections at airflow meter or throttle body.
9. Verify correct throttle position sensor adjustment and resistance value.

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. Ensure fuel system pressure is correct. Use ohmmeter to verify correct fuel injector resistance.
5. Check throttle bore for dirt or carbon.

ENGINE MISFIRES OR HAS LACK OF POWER (CARB)

1. Ensure fuel level is at specified mark on carburetor sight glass.
2. Verify sufficient fuel is dispensed at accelerator pump jets as throttle valve is opened.
3. Ensure fuel system pressure is correct.
4. Verify base timing is correct and timing advance system is functional.
5. Check EGR valve operation.
6. Check A/C cut-off system (if equipped).
7. Check carburetor mixture control duty cycle using dwell meter.

ENGINE MISFIRES OR HAS LACK OF POWER (EFI)

1. Verify air intake system is unrestricted.
2. Check EGR valve and solenoid for correct operation.
3. Check No. 1 and No. 2 purge control valve operation.
4. Check vacuum switching valve operation.
5. Check airflow meter for cracks.
6. Check airflow operation and resistance value.
7. Check atmospheric pressure sensor.
8. Check secondary air injection system (RX7).
9. Check Variable Dynamic Intake System (VDIS - RX7).
10. Check Variable Resonance Induction System (VRIS) for correct operation (MPV 3.0L, 929 SOHC & DOHC).
11. Check Variable Inertia Charge System (VICS) for correct operation (Protege 1.8L DOHC).
12. Verify connector at crank angle sensor has correct resistance values.
13. Check A/C cut-off system.
14. Check Triple Induction Control System (TICS) for correct operation (929 SOHC).
15. Ensure fuel system pressure is correct. Use ohmmeter to verify fuel injector terminal resistance.

Check turbo system for damage or wear (if equipped). Turbo system inspection should include the following components

1. Air by-pass valve
2. Engine Control Unit (ECU)
3. Intake air thermosensor in airflow meter
4. Knock sensor and knock control unit
5. Turbo wastegate solenoid valve.

ENGINE RUNS ROUGH ON DECELERATION (EFI)

1. Verify correct throttle body dashpot adjustment.
2. Check coolant thermosensor and throttle position sensor.
3. Check triple induction control system for correct operation (929 SOHC only).
4. Check air valve or ISC valve for malfunction.
5. Ensure fuel system pressure is correct.

AFTERBURN IN EXHAUST SYSTEM (CARB)

1. Verify base timing is correct and timing advance system is functional.
2. Verify that air intake system is clear of restrictions.
3. Check neutral switch (M/T) or inhibitor switch (A/T).
4. Check mixture control valve.
5. Verify dashpot disengages throttle lever at 1900-2100 RPM.
6. Check air cleaner reed valves.
7. Verify no leaks in exhaust system.

AFTERBURN IN EXHAUST SYSTEM (EFI)

1. Verify base timing is correct and timing advance system is functional.
2. Check throttle body dashpot adjustment.
3. Check secondary air injection system (RX7).
4. Check water thermosensor and throttle position sensor.
5. Check air valve, ISC switch and idle switch operation.
6. Check intake air system and throttle body electrical connections.
7. Ensure fuel system pressure is correct.
8. Verify no leaks in exhaust system.

POOR FUEL MILEAGE (CARB)

1. Verify correct carburetor idle and fuel mixture adjustment.
2. Verify base timing is correct and timing advance system is functional.
3. Ensure air intake system is unrestricted.
4. Verify choke is fully open after engine is warm.
5. Ensure fuel level is at specified mark on carburetor sight glass.
6. Check carburetor mixture control duty cycle using dwell meter.

POOR FUEL MILEAGE (EFI)

1. Verify correct throttle body dashpot adjustment.
2. Ensure correct throttle position sensor adjustment and resistance value.
3. Check intake air and water thermosensor.
4. Ensure fuel system pressure is correct.
5. Ensure exhaust system is unrestricted.

EXCESSIVE OIL CONSUMPTION

1. Check for restricted PCV system.
2. Check turbo system for malfunction.