P0302 Code: Cylinder 2 Misfire Detected

A P0302 code means the PCM has detected a misfire specifically on cylinder number 2. Unlike a P0300 (random misfire) that points to a system-wide problem, a cylinder-specific misfire code tells you exactly where to look. The PCM monitors crankshaft acceleration — each time a cylinder fires, it should produce a small acceleration of the crankshaft. When cylinder 2 fails to produce that acceleration, the PCM counts it as a misfire.

The great thing about a single-cylinder misfire code is that you can use swap tests to quickly narrow down whether the problem is ignition, fuel, or mechanical. Let us walk through the process.

What Causes a Cylinder 2 Misfire

A misfire on any single cylinder comes down to three things: spark, fuel, or compression. One of these three is missing or insufficient on cylinder 2.

Ignition Problems

• Failed ignition coil: On coil-on-plug (COP) systems, each cylinder has its own coil. A failed coil on cylinder 2 means no spark on that cylinder.
• Worn or fouled spark plug: Excessive gap, carbon fouling, oil fouling, or a cracked insulator. A plug that has been in there for 120,000 miles on a 100K plug application is suspect.
• Damaged spark plug wire (if equipped): On systems with plug wires, check for cracks, carbon tracking, or high resistance. A bad wire to cylinder 2 causes misfire on cylinder 2.
• Spark plug boot damage: Even on COP systems, the boot that connects the coil to the plug can crack, allowing spark to arc to ground instead of jumping the plug gap. Look for white or gray arcing marks inside the boot.

Fuel Problems

• Failed or clogged fuel injector: An injector that is electrically dead (open coil, bad connector) or mechanically clogged delivers no fuel or insufficient fuel to cylinder 2.
• Injector wiring issue: A broken wire, corroded connector, or bad PCM driver for the cylinder 2 injector circuit.

Mechanical Problems

• Low compression: A burned exhaust valve, broken valve spring, blown head gasket between cylinder 2 and a coolant passage, or a scored cylinder wall. Low compression means the cylinder cannot build enough pressure for proper combustion.
• Intake manifold gasket leak at runner 2: Unmetered air entering only the cylinder 2 runner causes a lean misfire on that cylinder.
• Carbon buildup on the intake valve (direct injection): On GDI engines, carbon builds up on the intake valve because there is no fuel washing over it. Heavy carbon on the cylinder 2 intake valve restricts airflow and disrupts the air/fuel mixture.

Step-by-Step Diagnosis

Step 1: Check Misfire Counters

Before you start swapping parts, connect your scan tool and look at misfire counters for all cylinders. Confirm that cylinder 2 is the only one with significant misfire counts. If multiple cylinders are misfiring, you may have a different problem — check our P0300 guide. Also note the misfire rate: occasional misfires (1-5 per 1,000 events) suggest an intermittent issue, while constant misfires (50 or more per 1,000 events) suggest a hard failure.

Step 2: Swap the Ignition Coil

This is the fastest way to test ignition. On COP systems, swap the coil from cylinder 2 with an adjacent cylinder (say, cylinder 4). Clear codes and run the engine. Watch misfire counters:

• Misfire moves to cylinder 4: The coil is bad. Replace it.
• Misfire stays on cylinder 2: The coil is not the problem. Move to the spark plug.

Step 3: Swap the Spark Plug

If the coil swap did not move the misfire, swap the cylinder 2 spark plug with an adjacent cylinder. Clear codes and run the engine:

• Misfire moves: Bad spark plug. Replace all plugs if they are at or near their service interval — if one failed, the others are close behind.
• Misfire stays on cylinder 2: Not an ignition issue. Move on to fuel.

Step 4: Test the Fuel Injector

Check the cylinder 2 injector:

• Listen with a stethoscope: Place the tip on each injector. They should all produce an even clicking sound. An injector that clicks weakly or not at all is suspect.
• Measure resistance: Unplug the injector and measure resistance across the terminals. Compare to spec and to the other injectors. They should all be within 0.5 ohms of each other. Most high-impedance injectors read 11-16 ohms.
• Check the injector pulse with a noid light: Unplug the injector and connect a noid light to the harness connector. Crank the engine — the noid light should flash evenly. If it does not flash on cylinder 2 but does on other cylinders, the problem is in the wiring or the PCM driver.
• Swap the injector (if accessible): On some engines, you can swap injectors between cylinders. If the misfire moves, the injector is bad.

Step 5: Check Compression

If ignition and fuel check out, test compression. A quick relative compression test using starter current draw or RPM variation gives you a fast comparison between cylinders. For a definitive answer, do a traditional compression test:

• Disable ignition and fuel injection.
• Remove the spark plug from cylinder 2.
• Thread in the compression gauge.
• Crank the engine for 4-6 compression strokes.
• Normal compression is typically 150-200 PSI depending on the engine. Compare cylinder 2 to the other cylinders — they should all be within 10% of each other. If cylinder 2 is 30% or more lower than the rest, you have a mechanical problem.

If compression is low, perform a wet test — add a tablespoon of oil to the cylinder through the spark plug hole and retest. If compression comes up significantly, the rings are worn. If it stays low, suspect a valve or head gasket issue.

Step 6: Check for Carbon Buildup (GDI Engines)

On direct injection engines, if compression is normal and ignition/fuel are good, carbon buildup on the cylinder 2 intake valve may be restricting airflow. This requires a borescope inspection through the intake runner or spark plug hole to visualize the valve. Heavy carbon requires walnut shell blasting or chemical cleaning — there is no shortcut for this one.

Common Mistakes

• Replacing the coil without swapping first. A swap test takes 5 minutes and gives you a definitive answer. Guessing at coils wastes money and time.
• Ignoring the spark plug boot. On COP systems, a cracked boot causes misfire even with a good coil and good plug. Always inspect the boot — and if you find coolant or oil in the spark plug well, fix the leak first (valve cover gasket on many engines). A plug sitting in oil or coolant will misfire.
• Not checking for oil or coolant in the spark plug well. A leaking valve cover gasket or tube seal allows oil to pool around the plug. This shorts the spark energy to ground and causes misfire. Fix the leak, replace the plug, and the misfire goes away.
• Skipping the compression test. If you have replaced the coil and plug and the misfire persists, do not keep throwing ignition parts at it. Check compression. A burned exhaust valve on cylinder 2 will not fix itself with new spark plugs.
• Not checking TSBs. Many engines have known cylinder-specific issues. Ford EcoBoost engines have had injector TSBs. GM Gen V V8s have had specific cylinder misfire TSBs related to valve train components. Check TSBs before going deep into diagnosis.

Confirming the Fix

After your repair, clear codes and run the engine. Watch misfire counters on your scan tool — cylinder 2 should show zero or near-zero misfires. Drive the vehicle through a variety of conditions: idle, acceleration, cruise, and deceleration. The code should not return. If the misfire was severe enough to trigger the catalytic converter over-temperature warning (flashing check engine light), drive gently for a while and monitor the catalytic converter — sustained misfires can damage the cat.

For more on misfire diagnostics and engine performance, check out the APEX Tech Nation Academy.