[old_master]

P0301 is in fact a miss on #1 cylinder. Aparently he didn't check O2 voltage in the freeze frame data, (that would indicate a lean or rich mixture when it missed). A lean reading would indicate the injector is not opening. A rich reading could mean the injector is stuck open or an ignition problem.

There are two ignition coil packs on your engine: One coil fires cylinders 1 & 4 and the other coil fires #2 & #3. When a coil fires, it fires both cylinders simultaneously. When one cylinder is firing on the compression stroke, the other is firing on the exhaust stroke. It is entirely possible for half of a coil to fail.

Here are some things to try that will narrow the problem down, but, they must be done in this order:

The first two steps will determine if a spark plug or a plug wire is faulty.

1. Swap #1 & #2 spark plugs, if the miss moves to cylinder #2, the spark plug is faulty.

2. Swap #1 plug wire with #2 plug wire and see if the miss moves to #2 cylinder. If the miss moves, the plug wire is faulty.

This step will determine if the coil is faulty:

Only at the ignition coil, (not the spark plugs) swap #1 & #4 plug wires. If the miss moves to cylinder #4, the coil is faulty.

If the miss stays on cylinder #1 after all this, the problem is with either the injector, the wire harness to the injector, or the ECM.


Post your results.