P0304 Code on Ford F150: Cylinder 4 Misfire Detected
Quick Answer: What is P0304?
On a Ford F150, the P0304 code means the engine computer has detected that Cylinder Number 4 is not firing properly. Because Ford engines use a "Coil-on-Plug" design, in 80% of cases, this is caused by a dead ignition coil or a fouled spark plug sitting directly on top of Cylinder 4. It is one of the easiest repairs to do at home.
1. Common Symptoms in a Ford F150
A single cylinder misfire on a heavy truck like the F150 creates very noticeable drivability issues:
- Engine Shaking or Shuddering: The truck will vibrate noticeably, especially when idling in gear or accelerating up a hill.
- Flashing Check Engine Light: Indicates severe catalyst-damaging misfires.
- Lack of Power: The truck feels like it is struggling to accelerate (because it is running on one less cylinder).
- Smell of Gas: A strong fuel odor coming from the exhaust pipe.
2. Most Likely Causes (Ranked by Probability)
Ford's EcoBoost and 5.0L Coyote engines are hard on ignition components. Start here:
- Bad Ignition Coil Pack (60% of cases): The coil pack sitting on Cylinder 4 has internally shorted out due to heat and age.
- Worn Spark Plug (30% of cases): The spark plug in Cylinder 4 has a cracked ceramic insulator or the electrode gap is too wide. (Very common on EcoBoost engines if they haven't been changed in 60,000 miles).
- Faulty Fuel Injector (5% of cases): The injector for Cylinder 4 is clogged or electrically dead.
- Low Compression (5% of cases): A mechanical issue like a burnt valve or blown head gasket (rare, but possible on high-mileage engines).
3. Step-by-Step Diagnostic and Fix
Step A: Locate Cylinder 4
On Ford F150s (V8 and V6), Cylinder 4 is always the one closest to the firewall (the windshield) on the passenger side of the engine. It is the furthest one back on the right side.
Step B: The Free "Coil Swap" Test
Before buying any parts, do this free diagnostic trick. Unbolt the ignition coil from Cylinder 4 (the bad one) and swap it with the ignition coil from Cylinder 1 (the very front cylinder on the same side). Clear the codes with your scanner and take the truck for a short drive until the Check Engine Light comes back on.
- If the code changes to P0301 (Cylinder 1 Misfire): The problem followed the coil. You have a bad ignition coil. Buy a new Motorcraft coil and replace it.
- If the code stays P0304 (Cylinder 4 Misfire): The coil is good. The problem is likely the spark plug. Remove the spark plug in Cylinder 4 and inspect or replace it.
4. Estimated Repair Costs
Diagnosing this yourself with the swap trick saves you the expensive diagnostic fee at a shop:
| Repair Type | Estimated Cost (USD) |
|---|---|
| Coil Swap Diagnostic | $0 (Free) |
| Replace 1 Spark Plug (DIY - Motorcraft) | $8 - $15 |
| Replace Ignition Coil Pack (DIY - OEM Part) | $40 - $80 |
| Diagnose & Replace Coil/Plug (Mechanic/Dealer) | $200 - $350+ |