Fuel Injector Buying Guide
Last updated: 24 April 2026
Fuel injectors deliver precisely metered fuel into the combustion chamber or intake port. Clogged, leaking, or electrically faulty injectors cause misfires, poor economy, and rough running. Modern diesel injectors also require coding to the ECU after replacement. At CarParts247 we stock petrol and diesel fuel injectors from Bosch, Siemens/VDO, and Delphi.
Petrol vs diesel injector faults
Petrol injectors operate at lower pressures (3-5 bar port injection, up to 200 bar direct injection). Diesel common-rail injectors operate at extreme pressures (up to 2,500 bar) and are precision-machined components.
- Misfire on one or more cylinders — blocked or electrically faulty injector
- Rough idle and uneven running — injector flow imbalance
- Diesel knock or rattle — injector not atomising fuel correctly
- Fuel smell or visible leak around the injector seat
- Black or white exhaust smoke — over-fuelling or incomplete combustion
Injector coding and maintenance
Diesel injectors have individual correction codes (IMA codes) that must be programmed into the ECU. Without coding, the engine may run rough, produce excess smoke, or damage the DPF.
- Diesel injectors: always code the new injector to the ECU using a diagnostic tool
- Replace copper injector sealing washers every time an injector is removed
- Clean the injector seat thoroughly before refitting to prevent combustion gas leaks
- Petrol injector cleaning additives can help prevent deposits on port-injection engines
- Direct-injection engines (petrol and diesel) are more sensitive to injector fouling
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Petrol and diesel injectors — misfire diagnosis, injector coding, and maintenance tips for long injector life.
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Frequently Asked Questions
Do diesel injectors need coding?
Yes. Each diesel injector has a unique correction code (IMA/C2I code) stamped on it. This must be programmed into the ECU using a diagnostic tool. Without coding, the engine runs incorrectly.
Can fuel injectors be cleaned?
Port-injection petrol injectors can often be cleaned with ultrasonic cleaning or fuel additive. Direct-injection and diesel injectors are harder to clean and may need specialist refurbishment or replacement.
How long do fuel injectors last?
Petrol injectors can last 100,000+ miles. Diesel injectors typically last 80,000-150,000 miles depending on fuel quality and maintenance. Regular fuel filter changes extend injector life.
What are the signs of a leaking injector?
Fuel smell around the engine, visible wetness at the injector seat, hard starting, and diesel knock. A leaking injector can also damage the DPF by allowing unburnt fuel into the exhaust.
How much does fuel injector replacement cost?
The price of fuel injectors depends on your exact vehicle and the brand you choose. Enter your registration above to see parts confirmed to fit, then compare prices from the brands we stock on this page. Free UK delivery on orders over £99.
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