P1340

What the Code Means

The DME logs a misfire in cylinder 1 specifically at the moment of engine startup. P1340 indicates that in the first seconds of operation, the cylinder isn't producing normal output.

Typical causes are a fouled spark plug, a failed ignition coil, or fuel delivery problems. A separate scenario involves a PCV system failure: on M60 engines, crankcase ventilation is routed near the rear cylinders, and when the PCV valve fails, oil reaches the cylinder 1 spark plug and fouls it.

Symptoms

Engine behavior:

• rough, labored startup;
• misfires after starting.

Indication:

• the Check Engine light comes on.

Additional:

• blue smoke from the exhaust at startup — a sign of oil burning, typical of a spark plug fouled by a failed PCV.

Diagnosis and Repair

1. Check the cylinder 1 spark plug and ignition coil. An oil-fouled or sooty plug with a good coil points to oil ingress, not an ignition system failure.
2. Inspect the PCV system for oil leaks.
3. Replace the PCV valve if it's faulty — on the M60 this is the root cause of rear-cylinder plug fouling.
4. Clear the codes and do a test start to confirm the misfire doesn't return.

Secondary Problems

Continuing to drive with persistent misfires:

• unburned fuel reaches the exhaust and damages the catalytic converter;
• the oxygen sensor degrades.

Oil fouling is dangerous on its own: oil in the combustion chamber can cause pre-ignition and detonation, which are destructive to the piston assembly. Don't put off the repair — the catalytic converter suffers first, then the risk of more serious mechanical damage sets in.