The OM611 was Mercedes' first common-rail diesel, powering the early Sprinter, C-Class, and E-Class. As a first-generation common-rail engine, injector failures are common on surviving examples due to age and mileage.
Rough idle with age-related wear: High-mileage OM611 injectors produce uneven idle due to worn nozzles and control valves.
Hard starting when cold: First-generation injectors lose atomisation quality, making cold starts progressively harder.
Black smoke under load: Worn nozzles over-fuel individual cylinders, producing black smoke when accelerating.
Fuel leak at injector seals: Age-degraded O-rings and sealing components allow diesel to leak externally.
Why OM611 injectors fail
fuel contamination
high-pressure wear cycles
carbon buildup
poor fuel quality
internal valve wear
How to diagnose OM611 injector faults
Read fault codes: Connect an OBD-II scanner and note any injector-related codes (P0201–P0204, P2146, P2149). This identifies which cylinder is affected.
Perform a leak-off test: Disconnect the fuel return pipes and route into measuring containers. Run the engine at idle for 60 seconds. Compare volumes per cylinder against manufacturer spec.
Listen for injector tick: Use a mechanic's stethoscope on each injector body. A dead or irregular tick indicates a stuck or failing solenoid.
Check fuel rail pressure: Monitor live fuel rail pressure data via diagnostic tool. Low pressure can mimic injector symptoms and may indicate a fuel pump issue instead.
Inspect for external leaks: Check around injector seals for signs of fuel or combustion gas leakage. Black carbon deposits indicate a blown seal.
Cylinder balance test: Use diagnostic software to run a cylinder contribution test. This electronically disables each injector in turn to measure its effect on engine speed.
OM611 injectors do not require electronic coding — they are plug-and-play. and torque to 7 Nm. Check fuel rail pressure sensor condition when replacing injectors.
No. The OM611 predates electronic injector coding. The injectors are direct-fit plug-and-play.
How much does it cost to replace OM611 injectors?
A set of four remanufactured injectors costs £350-£550. Labour is typically 2-3 hours.
Are OM611 injectors still available?
Yes. Remanufactured OM611 injectors are still widely available and are the recommended replacement option.
How much does it cost to replace injectors?
Replacement typically costs £150–£350 per injector depending on brand and engine. A full set of four with professional fitting usually costs £600–£1,200.
Can I drive with a faulty injector?
Driving with a faulty injector can cause engine damage, increased fuel consumption, DPF contamination, and oil dilution. We recommend diagnosis and replacement as soon as possible.
Do new injectors need coding?
Some vehicles require injector coding after replacement using manufacturer-specific diagnostic tools. Many Bosch solenoid units are plug and play. Check your engine guide for specific requirements.
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