Combustion misfire detected

P0301 - Cylinder #1

P0302 - Cylinder #2

P0303 - Cylinder #3

P0304 - Cylinder #4

P0305 - Cylinder #5

P0306 - Cylinder #6

Detection Condition

• The ECU determines which cylinder is misfiring by using the crankshaft position sensor to detect variations in the rotational speed of the crankshaft. While the engine is running, the ECU monitors the number of misfires that occur at 200 crankshaft revolution intervals and 1,000 crankshaft revolution intervals. Calculating the misfire ratio for each crankshaft revolution, if the ratio exceeds the preprogrammed threshold, the ECU determines that misfire significant enough to damage the catalyst(s) and/or negatively affect emissions performance has occurred.

Diagnostic Support Notes

• This is a continuous monitor (MISFIRE)
• Check engine indicator illuminates if the ECU detects that the above malfunction condition is negatively impacting emissions performance in two consecutive drive cycles
• PENDING CODE (emissions performance) is available
• Check engine indicator will flash if the ECU detects misfire capable of causing damage to catalytic converters during the first drive cycle
• PENDING CODE (catalyst protection) is not available
• FREEZE FRAME DATA is available
• DTC is stored in ECU memory

Possible Causes

• Spark plug incorrect gap or malfunction
• COP unit malfunction (KJ) / high-tension lead or distributor/coil unit malfunction (KL)
• Fuel injector malfunction (electrical or mechanical)
• Intake leak between dynamic chamber and cylinder head (KJ)
• Low cylinder compression (failed head gasket, burnt exhaust valve)
• Related connector or terminal malfunction
• Related wiring harness malfunction

Diagnostic Procedure

1.  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.  Check for related TSBs and/or online repair information.  Is any repair information available?

• Yes - Perform repair or diagnosis according to available repair information.  If vehicle is not repaired, go to next step.
• No - Go to next step.

3.  Turn ignition key to OFF then ON (engine off).  Any other pending or current DTCs present?

• Yes - Go to appropriate DTC troubleshooting.
• No - Go to next step.

4.  With an OBD interface, access engine coolant temperature (ECT), intake air temperature (IAT), mass airflow (MAF), engine revolutions per minute (RPM), throttle position (TP), and vehicle speed (VS) PIDs.  Is there any signal that is far out of specification when ignition switch is ON and engine is idling?

• Yes - Inspect suspected circuit and/or part according to inspection results, then go to Step 13.
• No - Go to next step.

5.  Inspect same PIDs as in 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 13.
• No - Go to next step.

6.  Turn ignition key to OFF.  Remove spark plug from suspected cylinder and check for cracks, excessive wear, incorrect gap, or fuel saturation.  Is there a problem with the spark plug condition?

• Yes - If spark plug is wet, fuel flooding is suspected.  Go to Step 12.  If spark plug is damaged, replace faulty plug then go to Step 13.
• No - Go to step 7a (2.3L KJ engine) or step 7b (2.5L KL engine).

7a.  KJ Engine:  Remove coil-on-plug unit from suspected cylinder and inspect insulator for cracks or heat damage from sparks shorting to cylinder head.  Swap the COP unit with one from another cylinder to determine if the misfire DTC moves to the cylinder with the suspected COP unit.  Is COP unit okay?

• Yes - Go to Step 8.
• No - Replace defective part, then go to Step 13.

7b.  KL Engine:  Remove high tension lead from suspected cylinder and inspect insulator for cracks or heat damage from sparks shorting to cylinder head.  Inspect high tension lead condition and resistance.  Inspect distributor rotor for wear or damage.  Inspect distributor cap for wear or damage.  Inspect for proper operation of the ignition coil within the distributor unit.  Are all items okay?

• Yes - Go to Step 8.
• No - Replace defective part, then go to Step 13.

8.  Inspect for air leakage between the dynamic chamber and intake manifold (KJ) and between the intake manifold and cylinder head.  Is air leakage found?

• Yes - Repair or replace suspected part, then go to Step 13.
• No - Go to next step.

9.  Remove intake-air system parts.  Disconnect fuel injector connector on suspected cylinder.  Connect noid light to fuel injector connector terminals.  Does the light indicate normal fuel injector operation while cranking?

• Yes - Go to next step.
• No - Check fuel injector harnesses.  Repair or replace if necessary, then go to Step 13.

10.  Remove radiator cap after engine has cooled sufficiently, implement system bleed procedure, then idle engine.  Are there any small bubbles, which make the engine coolant appear white at the filler opening?

• Yes - Air from combustion chamber is entering cooling system.  Repair or replace faulty parts, then go to Step 13.
• No - Go to next step.

11.  Inspect engine compression.  Is engine compression okay?

• Yes - Go to next step
• No - Overhaul the engine, then go to Step 13.

12.  Remove fuel injector from suspected cylinder and swap it with one from another cylinder.  Start the engine and run it at idle.  Does misfire DTC move to cylinder with suspected injector?

• Yes - Replace injector, then go to Step 13.
• No - Go to next step.

13.  Make sure to reconnect all disconnected connectors.  Start engine, clear DTC from ECU memory using OBD interface and perform DRIVE MODE 1.  Is a PENDING CODE for the same DTC present?

• Yes - Replace ECU.
• No - Go to next step.

14.  Perform "After Repair Procedure" and scan for stored codes.  Is there a DTC present?

• Yes - Go to appropriate DTC troubleshooting.
• No - Troubleshooting completed.

[P0301 / P0302 / P0303 / P0304 / P0305 / P0306 - From 2002 Mazda Millenia factory service manual]