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Drew
Drew, Super Mazda Tech.
Category: Mazda
Satisfied Customers: 2518
Experience:  19 yrs. experience. Mazda Senior Certified Tech, with Ford, Linc. & Merc. experience. ASE L1 Advanced Certified Master Tech.
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Mazda Miata: I have 2000 Miata that will get a random misfire

Resolved Question:

I have 2000 Miata that will get a random misfire code (check engine) and will cut out. It will not restart for some time but will after it sits. Mechanics have replaced fuel pump twice, catalytic converter, O2 sensors, plug wires. The fuse to the fuel pump has also blown once. Many times mechanics can't find anything wrong as the "Check Engine" light clears and the vehicle runs like a top. I've already dropped over $3K trying to get this fixed.
Submitted: 2 years ago.
Category: Mazda
Expert:  Michelle-Mod replied 2 years ago.


Hi, I’m a moderator for this topic and I wonder whether you’re still waiting for an answer. If you are, please let me know and I will do my best to find a Professional to assist you right away. If not, feel free to let me know and I will cancel this question for you. Thank you!


Customer: replied 2 years ago.
What information do they need?
Customer: replied 2 years ago.
Yes. still waiting. It said they needed additional info, but I never saw what info they wanted.
Expert:  Drew replied 2 years ago.
Welcome to Just Answer. My name is XXXXX XXXXX I will be glad to assist you.

Sorry for the delay in answering your question.

If you are getting a random misfire code P0300, I suspect a faulty crankshaft positions sensor or camshaft position sensor.

Also seen several faulty computer on this vehicle when hot. You can try to duplicate the concern by heating the computer with a blow dryer and see if it will stall. Also with the engine running, try flexing the computer connector and wiggle the wiring harness.

Here is a list of other possible causes for P0300. All will need to be inspected.

Please let me know if you have any additional questions by hitting the reply button.

Thanks
Drew



DTC P0300

Random misfire detection

DETECTION CONDITION

  • PCM monitors CKP sensor input signal interval time. PCM calculates the change of the interval time for each cylinder. If the change of interval time exceeds the preprogrammed criteria, PCM detects a misfire in the corresponding cylinder. While the engine is running, PCM counts the number of misfires that occurred at 200 crankshaft revolutions and 1,000 crankshaft revolutions and calculates misfire ratio for each crankshaft revolution. If the ratio exceeds the preprogrammed criteria, PCM determines that a misfire, which can damage the catalytic converter or affect emission performance, has occurred.

    Diagnostic support note
  • This is a continuous monitor (MISFIRE).

  • MIL illuminates if PCM detects the misfire which affects emission performance in two consecutive drive cycles.

  • PENDING CODE is available if PCM detects the misfire which affects emission performance during first drive cycle.

  • MIL flashes if PCM detects the misfire which can damage the catalytic converter during first drive cycle. Therefore, PENDING CODE is not available while MIL flashes.

  • FREEZE FRAME DATA is available.

  • DTC is stored in the PCM memory.

POSSIBLE CAUSE

  • CKP sensor malfunction

  • CMP sensor malfunction

  • Ignition coil malfunction

  • High-tension lead malfunction

  • Mass airflow sensor contamination

  • Excess air suction in intake‐air system (between mass air flow sensor and dynamic chamber)

  • Fuel pump malfunction

  • Fuel pressure regulator malfunction

  • Fuel line clogged

  • Fuel filter clogged

  • Fuel leakage in fuel line

  • Purge control solenoid valve malfunction

  • PCV valve malfunction

  • EGR valve malfunction

  • Vacuum hoses damages or improper connection

  • Related connector and terminal malfunction

  • Related wiring harness malfunction


Diagnostic procedure


STEP

INSPECTION

ACTION

1

VERIFY FREEZE FRAME DATA HAS BEEN RECORDED
  • Has FREEZE FRAME DATA been recorded?

Yes

Go to next step.

No

Record FREEZE FRAME DATA on repair order, then go to next step.

2

VERIFY RELATED REPAIR INFORMATION AVAILABILITY
  • Check for related Service Bulletins and/or on-line repair information availability.

  • Is any related repair information available?

Yes

Perform repair or diagnosis according to available repair information.

  • If vehicle is not repaired, then go to next step.

No

Go to next step.

3

VERIFY RELATED PENDING CODE OR STORED DTCs
  • Turn ignition key to OFF then ON (Engine OFF).

  • Verify related pending code or stored DTCs.

  • Is other DTCs present?

Yes

Go to appropriate DTC troubleshooting.

» DTC TABLE

No

Go to next step.

4

VERIFY CURRENT INPUT SIGNAL STATUS (IGNITION KEY TO ON/IDLE)
  • Access BRK SW, ECT V, IAT V, MAF V, RPM, TP V, and VS PIDs using NGS tester.

    » ENGINE CONTROL SYSTEM INSPECTION

  • Is there any signal that is far out of specification when ignition switch is ON and engine runs at idle?

Yes

Inspect suspected circuit and/or part according to inspection results, then go to Step 22.

» ENGINE CONTROL SYSTEM INSPECTION

No

Go to next step.

5

VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION
  • Inspect same PIDs with step 4 while simulating FREEZE FRAME DATA condition.

  • Is there any signal which causes drastic changes?

Yes

Inspect suspected circuit and/or part according to inspection results, then go to Step 22.

» ENGINE CONTROL SYSTEM INSPECTION

No

Go to next step.

6

INSPECT CMP SENSOR

Yes

Go to next step.

No

Inspect installation condition and damage on timing belt and gears, repair faulty parts.

  • If it is okay, replace CMP sensor.

Then go to Step 22.

7

VERIFY CKP SENSOR INSTALLATION CONDITION
  • Check for CKP sensor looseness.

  • Is CKP sensor loose?

Yes

Retighten CKP sensor, then go to Step 22.

No

Go to next step.

8

CHECK IGNITION COIL OPERATION AND HIGH-TENSION LEAD WITH TIMING LIGHT
  • Verify blinking condition on each cylinder using timing light at idle.

  • Do all cylinders show blinking condition?

Yes

Go to Step 12.

No

Go to next step.

9

CHECK HIGH-TENSION LEADS OF NO BLINKING CYLINDER
  • Turn ignition key to OFF.

  • Inspect high-tension leads for installation condition, corrosion on terminal, open lead and damaged cover.

  • Is condition of high-tension lead okay?

Yes

Go to next step.

No

Replace faulty high-tension lead, then go to Step 22.

10

INSPECT POWER SUPPLY TERMINAL AT IGNITION COIL CONNECTOR
  • Disconnect ignition coil connector.

  • Turn ignition key to ON (Engine OFF).

  • Measure voltage between ignition coil terminal A (harness-side) and body ground.

  • Is there voltage reading B+?

Yes

Go to next step.

No

Check for open circuit between ignition coil connector and ignition switch. Repair or replace wiring harness, then go to Step 22.

11

INSPECT IGNITION COIL RESISTANCE

Yes

Go to Step 22.

No

Replace ignition coil, then go to Step 22.

12

INSPECT MAF V PID
  • Start engine.

  • Access MAF V PID using NGS tester.

  • Verify that MAF V PID changes quickly according to race engine RPM.

  • Is MAF V PID response okay?

Yes

Go to next step.

No

Replace mass airflow sensor, then go to Step 22.

13

INSPECT EXCESSIVE AIR SUCTION IN INTAKE‐AIR SYSTEM
  • Inspect for air leakage at following:

    • Between mass air flow sensor and throttle body

    • Between throttle body and dynamic chamber

  • Is there any malfunction?

Yes

Repair or replace suspected part, then go to Step 22.

No

Go to next step.

14

INSPECT FUEL LINE PRESSURE

Yes

Go to Step 17.

No

If fuel line pressure is excess high, check as follows:

  • Fuel pump maximum pressure

    » FUEL PUMP INSPECTION

  • Fuel return line for clogged

    • If all above are okay, replace pressure regulator.

Then go to Step 22.

If fuel line pressure is too low, go to next step.

15

INSPECT FUEL PUMP MAXIMUM PRESSURE
  • Inspect fuel pump maximum pressure.

    » FUEL PUMP INSPECTION

  • Is fuel pump maximum pressure less than 640 kPa {6.5 kgf/cm 2, 92 psi}?

Yes

Go to next step.

No

Inspect fuel pump circuit for open or poor connection. Repair or replace suspected circuit, then go to Step 22.

  • If okay, replace fuel pump, then go to Step 22.

16

INSPECT FUEL LINE FROM FUEL PUMP TO FUEL DELIVERY PIPE
  • Visually inspect for fuel leakage in fuel line.

  • Is any fuel leakage found?

Yes

Replace suspected fuel line, then go to Step 22.

No

Inspect fuel filters for following:

  • Restriction or clogging at fuel filter (high-pressure side).

  • Foreign materials or stain inside fuel filter (low-pressure side)

Perform following actions as result.

  • If restriction or clogging is found at fuel filter (high-pressure side), replace fuel filter.

  • If foreign materials or stain is found inside fuel filter (low-pressure side), clean of fuel tank and filter.

  • If all items above are okay, replace pressure regulator.

Then, go to Step 22.

17

INSPECT ENGINE COMPRESSION

Yes

Go to next step.

No

Implement engine overhaul for repairs, then go to Step 22.

18

INSPECT OPERATION OF PURGE CONTROL SOLENOID VALVE
  • Turn ignition key to OFF.

  • Connect vacuum pump to purge control solenoid valve and apply vacuum to solenoid.

  • Verify that solenoid holds vacuum.

  • Turn ignition key to ON (Engine OFF).

  • Access PRGV PID in SIMULATION TEST using NGS tester.

  • Set duty value to 100% for PRGV PID.

  • Apply vacuum while turning solenoid from OFF to ON simulating PRGV PID with 100% duty value.

  • Verify that solenoid releases vacuum while solenoid is turned ON.

  • Is purge control solenoid valve operation okay?

Yes

Go to next step.

No

Replace purge control solenoid valve, then go to Step 22.

19

INSPECT PCV VALVE OPERATION
  • Turn ignition key to OFF.

  • Remove PCV valve and check valve operation.

    » PCV VALVE INSPECTION

  • Is PCV valve operation okay?

Yes

Replace PCV valve, then go to Step 22.

No

Go to next step.

20

INSPECT OPERATION OF EGR VALVE
  • Remove EGR valve.

  • Visually check for stuck open condition.

  • Is EGR valve stuck open?

Yes

Repair or replace EGR valve, then go to Step 22.

No

Go to next step.

21

INSPECT SEALING OF ENGINE COOLANT PASSAGE

WARNING:

  • Removing radiator cap when radiator is hot is dangerous. Scalding coolant and steam may shoot out and cause serious injury.

  • When removing radiator cap, wrap thick cloth around and turn it slowly.

  • Remove radiator cap.

  • Implement procedure to bleed air from engine coolant, then run engine at idle.

  • Are there any small bubbles which makes engine coolant white at filling opening?

    NOTE:

    • Large bubbles are normal since they are remaining air coming out from engine coolant passage.

Yes

Air gets in from poor sealing on head gasket or other areas between combustion chamber and engine coolant passage. Repair or replace faulty parts, then go to next step.

No

Go to next step.

22

VERIFY TROUBLESHOOTING OF MISFIRE DTC COMPLETED
  • Make sure to reconnect all disconnected connectors.

  • Turn ignition key to ON (Engine OFF).

  • Clear DTC from memory using NGS tester generic OBD-II function.

  • Start engine and perform DRIVE MODE 1.

    » Mode 1 (PCM Adaptive Memory Produce Drive Mode)

  • Is PENDING CODE of same DTC present?

Yes

Replace PCM, then go to next step.

No

Go to next step.

23

VERIFY AFTER REPAIR PROCEDURE

Yes

Go to applicable DTC inspection.

» DTC TABLE

No

Troubleshooting completed.

Drew, Super Mazda Tech.
Category: Mazda
Satisfied Customers: 2518
Experience: 19 yrs. experience. Mazda Senior Certified Tech, with Ford, Linc. & Merc. experience. ASE L1 Advanced Certified Master Tech.
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