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.

Reading P0304 on a Ford properly

A generic reader will show P0304 and nothing else. What matters is the freeze-frame data stored with it — engine speed, load, coolant temperature and fuel trims at the moment the fault was logged — plus whether any other module on the Ford has logged something at the same time. Codes rarely arrive alone, and the order they were stored in usually points at which one is the cause and which are the consequences.

Clearing P0304 without fixing it

Erasing the code resets the Ford's readiness monitors as well as the light. The fault returns on the next drive cycle if the cause is still there, and in the meantime the incomplete monitors can stop the car passing an emissions check. After a genuine repair, the car is driven until the relevant monitor completes before it is handed back.

Bob's Mechanical Repairs is an independent garage in Birnam, Dunkeld, Perthshire, with 32 years of Bob's experience on the tools. If P0304 is showing on your Ford, bring any scan results with you — we will read the live data ourselves, confirm which cause it actually is, and price the repair before any work starts.