Can anyone help me understand what all of this means? I get the general idea but I don't know how to turn the data into something I can understand to help me diagnose what is wrong with my car. I have a P0304 error code on a 2004 3s 2.3L and it's been on for a while. I've tried new spark plugs, new fuel injectors, replace the O2 sensors, checked the vacuum lines for leaks. Any information to help me make sense of this data is welcome.

Freeze Frame
-P0304: Cylinder 4 Misfire Detected (Powertrain, Generic)
-Fuel system status: Fuel system A: Closed loop (1)
-Fuel system status: Fuel system B: NA
-Calculated engine load: 22.0 %
-Engine Coolant Temperature: 114 °F
-Short Term Fuel Trim - Bank 1: -8.6 %
-Long Term Fuel Trim - Bank 1: 13.3 %
-Intake Manifold Absolute Pressure: 8.9 inHg
-Engine RPM: 1132 RPM
-Vehicle Speed Sensor: 6 mph
-Ignition Timing Advance for #1 Cylinder: -2.5
-Intake Air Temperature: 68 °F
-Air Flow Rate from Mass Flow Sensor: 0.6 lb/min
-Absolute Throttle Position: 13.7 %
-Time Since Engine Start: 0 min 56 s
-Commanded EGR: 0.0 %
-Commanded Evaporative Purge: 0.0 %
-Fuel Level Input: 18.0 %
-Number of warm-ups since DTCs cleared: 1
-Distance traveled since DTCs cleared: 1 miles
-Barometric Pressure: 29.2 inHg
-Catalyst Temperature Bank 1, Sensor 1: 743 °F
-Control module voltage: 14.13 V
-Absolute Load Value: 17.3 %
-Fuel/Air Commanded Equivalence Ratio: 1.000
-Relative Throttle Position: 4.7 %
-Absolute Throttle Position B: 14.1 %
-Accelerator Pedal Position D: 7.8 %
-Accelerator Pedal Position E: 8.2 %
-Commanded Throttle Actuator Control: 4.7 %

 

Hmmm, what engine do you really have in your car; the 2004 Mazda3 s didn't come with a 2.5 liter motor.

 

Sorry, I've changed it to 2.3L. That was my mistake when typing.

 

P0304 is cylinder 4 misfire, is it coil on plug ignition? Have you swapped the coil to another cylinder? Maybe swap the plugs around, just to rule out a dodgy new plug.

Have you carried out a compression test?

What do all the spark plugs look like after a long drive?

Cold be a wiring fault for the coil or injector.

 

I have tried swapping the coils and the plugs with the problem not changing. Haven't done a compression test. I'll check the spark plugs after work today and rent a compression tester.

 

It is coil on plug. Spark plugs all look normal. I just did a compression test and one cylinder was 50% of the others. When standing in front of the car facing engine it is the cylinder all the way on the right.

 

Everything looks fine except the cylinder on the drivers side has 50% compression compared to the rest of the cylinders.