Ford P0304

Cylinder 4 misfire on Ford — coil-pack failure on EcoBoost, glow-plug/injector on TDCi, or carbon-fouled plug on Duratec.

Ford P0304 — Cylinder 4 misfire on Ford — coil-pack failure on EcoBoost, glow-plug/injector on TDCi, or carbon-fouled plug on Duratec. Typical UK independent garage cost: £80–£480.

What actually causes P0304 on a Ford

On Ford 1.6/2.0 EcoBoost cyl 4 is the rearmost cylinder and the coil pack runs hottest — fails first, by 60k miles typically. On 2.0 TDCi diesels cyl 4 misfire is usually a failed glow plug (no smoke from start) or a tired injector (smoke). On older Duratec 1.6/2.0 petrols it's typically a fouled spark plug or perished HT lead.

Ford engines that log P0304

• 1.0 EcoBoost (Fiesta, Focus, B-Max — 3-cyl so cyl 4 = rare extended variants)
• 1.6 EcoBoost (Focus, Kuga)
• 2.0 EcoBoost (Mondeo, Kuga)
• 1.6/2.0 TDCi (Focus, Mondeo, Transit)

How we diagnose P0304 on a Ford

1. FORScan — read misfire counter per cylinder, isolate the bad cylinder
2. Swap coil pack from cyl 4 to cyl 1 (EcoBoost) — code follows the coil if coil is at fault
3. Pull spark plug and inspect for oil/carbon (Duratec) or carbon (EcoBoost)
4. On TDCi, test glow plug and injector return-flow
5. Replace failed component and clear codes

The common misdiagnosis to avoid

Don't replace all 4 coils as a set on EcoBoost when only cyl 4 has failed — swap cyl 4's coil with cyl 1, if the misfire follows the coil, replace just that one.

Ford P0304 repair cost in the UK

Expect £80–£480 including parts and labour at an independent garage. Main-dealer quotes on Ford are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.

Bob's workshop tip

On 1.6 EcoBoost ST-Line with cyl 4 misfire, also check the coolant level — these engines have a known head crack issue and a misfire on cyl 4 plus disappearing coolant is the early warning sign. Catching it early saves a £4,000 engine.

Codes usually seen alongside P0304 on Ford

• P0300
• P0301
• P0302
• P0303

Symptoms drivers report with P0304

• Engine warning light flashing (not steady) under load
• Noticeable juddering at idle in gear
• Smell of unburnt fuel from the exhaust
• Misfire worse when engine is cold and damp
• Significantly reduced power

Repairs that clear P0304

• Plug & coil replacement

For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0304 guide.