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Home >> Mazda >> 2001 >> MX-5 Miata Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0300: Random Misfire Detected >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

  1. Ensure FREEZE FRAME DATA has been recorded. Check for related service bulletins. Repair as necessary and go to next step.
  2. Turn ignition off and on. Using scan tool, check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If no other DTCs are present, go to next step. If DTCs are present, go to appropriate test.
  3. Start engine and allow to idle. Using scan tool, access PID data for BRK SW, ECT V, IAT V, MAF V, RPM, TP V and VS. Ensure all signal data is within specification. See PIN VOLTAGE/PID VALUE CHARTS article. If all PID data is within specification, go to next step. If any PID data is not within specification, go to applicable test in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article and go to step  20.
  4. Referring to FREEZE FRAME DATA, operate vehicle under same conditions as when DTC was set. Record PID data for BRK SW, ECT V, IAT V, MAF V, RPM, TP V and VS. If all PID data is within specification, go to next step. If any PID data is not within specification, go to applicable test in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. Diagnose and repair as necessary and go to step  20.
  5. Check CMP sensor operation. See BASIC DIAGNOSTIC PROCEDURES article. If CMP sensor is operating appropriately, go to next step. If CMP sensor is not operating appropriately, ensure CMP sensor is installed correctly, and timing belt and gears are not damaged before replacing CMP sensor and go to step  20.
  6. Check CKP sensor installation. See BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary and go to step  20. If sensor is tight, go to next step.
  7. Check primary and secondary ignition system. See BASIC DIAGNOSTIC PROCEDURES article. If both primary and secondary ignition system is okay, go to step  10. If secondary ignition system is not operating properly, repair or replace as necessary. If primary ignition system is not operating properly, go to next step.
  8. Disconnect ignition coil connector. Turn ignition on. Measure voltage at coil harness connector terminal "A" (Black/White wire). If battery voltage is present, go to next step. If battery voltage is not present, repair open in Black/White wire between ignition switch and ignition coil. See WIRING DIAGRAMS article. Go to step  20.
  9. Check ignition coil resistance. See BASIC DIAGNOSTIC PROCEDURES article. If coil is okay, go to step  20. If coil is faulty, replace ignition coil and go to step  20.
  10. Start engine. Using scan tool, check MAF V PID while revving engine. If MAF V PID changes quickly, go to next step. If MAF V PID does not change quickly, replace MAF sensor and go to step  20.
  11. Check for vacuum leaks between MAF sensor and throttle body. Also check for vacuum leaks at throttle body and plenum chamber. Repair or replace as necessary and go to step  20. If no problem is found, go to next step.
  12. Check fuel line pressure. See BASIC DIAGNOSTIC PROCEDURES article. If fuel line pressure is okay, go to step  15. If fuel line pressure is low, go to next step. If fuel pressure is high, check fuel pump maximum pressure. See BASIC DIAGNOSTIC PROCEDURES article. If fuel pump maximum pressure is okay, check for a plugged fuel return line. If fuel return line is okay, replace pressure regulator and go to step  20.
  13. Check fuel pump maximum pressure. See BASIC DIAGNOSTIC PROCEDURES article. If maximum pressure is less than 92 psi (6.4 kg/cm2 ), go to next step. If maximum pressure is not less than 92 psi (6.4 kg/cm2 ), repair wiring. If wiring is okay replace fuel pump and go to step  20.
  14. Check for leaks in fuel system downstream of fuel pump. If any leaks are found, repair as necessary. If no leaks are found, check for plugging at fuel filter and fuel inlet filter (sock). If plugging is present, check fuel tank for debris. If fuel tank is okay, replace fuel filter and go to step  20. If fuel tank has debris, clean tank, replace fuel inlet filter (sock) and fuel filter. If fuel tank, fuel filter and fuel inlet filter (sock) are okay, replace fuel pressure regulator and go to step  20.
  15. Check engine compression. Engine compression should be a minimum of 146 psi (10.22 kg/cm2 ) at 300 RPM with a maximum variation of 28 psi (2 kg/cm2 ). If compression is as specified, go to next step. If compression is not as specified, repair as necessary and go to step  20.
  16. Turn ignition off. Disconnect purge solenoid valve hoses. Purge solenoid valve is located at right side of engine compartment, above catch tank, next to windshield washer reservoir. Disconnect purge solenoid valve connector. Connect vacuum pump to one side of purge solenoid valve. Apply vacuum. Purge solenoid valve should hold vacuum. Apply power and ground to purge solenoid valve. Purge solenoid valve should not hold vacuum. If purge solenoid valve operates as specified, go to next step. If purge solenoid valve does not operate as specified, replace purge solenoid valve and go to step  20.
  17. Check PCV system. If PCV system is okay, go to next step. If problem is found, repair as necessary and go to step  20.
  18. Ensure EGR valve is not stuck open. See applicable test in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. If no problems are found, go to next step. If EGR valve is stuck open, replace or repair as necessary and go to step  20.
  19. Check cooling system for combustion gases. If no problem is found, go to next step. If combustion gases are found in cooling system, repair leak and go to next step.
  20. Reconnect all connectors. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Conduct PCM adaptive memory drive mode. See DRIVE MODES  under SELF-DIAGNOSTIC SYSTEM. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If DTC P0300 is present, replace PCM and go to next step. On vehicles equipped with immobilizer system, reprogram ignition key identification numbers. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. If DTC P0300 is not present, go to next step.
  21. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If no other DTCs are present, testing is complete. If any other DTCs are present, go to applicable test and repair.
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