Ford Expedition P0300: Random or Multiple Cylinder Misfire Detected
Quick Answer: What is P0300?
On a Ford Expedition, the P0300 code triggers when the PCM detects multiple cylinders are failing to fire. In the 3.5L EcoBoost and 5.4L Triton V8, this is overwhelmingly caused by worn-out spark plugs, moisture in the spark plug wells, or failing ignition coils.
Common Symptoms
- Engine Shuddering: The vehicle shakes, especially under heavy load or while towing.
- Lack of Power: Significant hesitation when merging onto the highway.
- Rough Idle: The engine feels "lumpy" at stoplights.
- Reduced MPG: The engine wastes fuel because it isn't burning it efficiently.
Most Likely Causes
- Failed Ignition Coils (45%): Ford "Coil-on-Plug" units are prone to heat failure, especially on the back cylinders of the engine.
- Old Spark Plugs (30%): EcoBoost engines are very hard on plugs; they often need replacement every 40,000 to 60,000 miles.
- Moisture Intrusion: Water getting into the spark plug wells after a heavy rain or engine wash.
- Vacuum Leak: A cracked PCV hose or intake manifold gasket.
Detailed Repair Cost Breakdown
Estimates for Ford Expedition (3.5L and 5.4L) in the US market:
| Component / Task | Aftermarket Part | OEM Motorcraft Part | Labor Time |
|---|---|---|---|
| Ignition Coil (Each) | $45 - $75 | $115 - $160 | 0.5 - 1.5 hrs |
| Spark Plugs (Set of 6 or 8) | $60 - $100 | $120 - $180 | 1.5 - 3.0 hrs |
How to Fix P0300 on a Ford Expedition
1. The "Coil Swap" Diagnostic
If your scan tool shows a specific misfire (like P0302), swap the ignition coil with its neighbor. If the code moves (e.g., to P0303), the coil is dead. For the Expedition, always use Genuine Motorcraft coils. Aftermarket coils are famous for causing "radio interference" and misfires on Ford trucks.
2. Gap Your Plugs Correctly
If you have an EcoBoost 3.5L engine, the spark plug gap is critical due to the turbo pressure. Ensure your new plugs are gapped precisely to 0.028 - 0.030 inches. Even "pre-gapped" plugs from the box are often wrong and will cause a P0300 code under acceleration.
3. Inspect the PCV Hose
On the older 5.4L engines, look at the rubber elbow of the PCV hose at the back of the intake manifold. They are notorious for dry-rotting and cracking. A vacuum leak here will cause a "lean misfire" (P0300 and P0171). Replacing this $30 hose is a very common and easy fix.