Cylinder 1 Misfire Detected

Same misfire detection as P0300, but the PCM has pinned it to cylinder 1. That makes diagnosis way easier — you only have to test what's unique to that cylinder. Three things make a cylinder fire: spark, fuel, and compression. Swap, test, eliminate. Don't throw parts. If the misfire follows a swapped coil or injector, that part is the problem. If it stays on cylinder 1 after both swaps, you're looking at compression — burned valve, broken ring, blown head gasket, or a bent pushrod. Same diagnostic logic applies to P0302–P0308, just on a different cylinder.

Crankshaft deceleration during cylinder 1's power stroke exceeds the misfire threshold. Counts logged per-cylinder; P0301 sets when cylinder 1's count crosses the emissions limit.

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 1Swap the cylinder 1 coil with cylinder 2 (or any neighbor). Clear codes, drive. If misfire moves to cylinder 2 — coil is bad.
2. 2If coil swap didn't move it, swap the injector with a neighbor. If misfire moves — injector. (Note: not all platforms allow easy injector swap.)
3. 3Pull the cylinder 1 plug. Look at it. Oil-fouled = valve seal/rings. Wet with fuel = ignition issue or dead injector. White and clean = lean misfire or coolant intrusion (head gasket).
4. 4If coil and injector both check good, run a compression test on cylinder 1. Low and dry = valve/ring. Low and rises with oil added = rings. Low with bubbles in coolant = head gasket.
5. 5Cylinder leakdown will tell you exactly where compression is escaping: intake (carb noise at throttle body), exhaust (hiss at tailpipe), rings (air at oil cap), head gasket (bubbles in coolant).
6. 6Don't ignore the wiring. A chafed coil wire or loose injector connector mimics a failed part perfectly. Wiggle-test with a scope on the signal.

• Failed ignition coil on cylinder 1
• Fouled, cracked, or worn spark plug on cylinder 1
• Clogged or leaking injector on cylinder 1
• Burned exhaust valve / low compression on cylinder 1
• Cracked plug well filling with water/oil (Ford Triton, Hemi, others)
• Broken valve spring or worn cam lobe affecting cylinder 1
• Wiring or connector issue at coil/injector for cylinder 1

Plug $10–$40. Coil $80–$300. Injector $150–$500. Valve job $1,500–$3,500. Head gasket $1,500–$3,000.