Mercedes C-Class Fuel Injector Replacement: Misfire Fixed at 251,000km

This Mercedes C-Class came in with an engine misfire that two rounds of new spark plugs and ignition coils had not cured. We replaced all four fuel injectors. Two days later, the owner confirmed: no misfire.

Job completed: September 2026

Four new fuel injectors on their boxes and the four old injectors on the fuel rail, on our workshop floor

Job completed: September 2026. Last updated: October 2026. Written from our workshop job records and photos; technical details are generalised where the records do not confirm them.

Car: Mercedes-Benz C-Class
Mileage: About 251,000km
Symptom: Engine misfire, still there after two rounds of new spark plugs and coils
Found: Stored misfire codes P030085 and P030385, the second for cylinder 3
Fix: All four fuel injectors replaced with OEM-grade parts
Outcome: The owner reported no misfire two days later

Car	Mercedes-Benz C-Class, about 251,000km
Symptom	Engine misfire after two rounds of new spark plugs and ignition coils
Fault found	Misfire codes P030085 and P030385 stored; our team advised replacing the fuel injectors first
Repair done	All four fuel injectors replaced with OEM-grade parts
Parts	OEM-grade fuel injectors
Time taken	Timeline confirmed when you book
Cost	Quoted and approved before work began
Warranty	No warranty term stated for this job

What the owner reported

The owner brought in this Mercedes C-Class with an engine misfire. The car was at about 251,000km. The owner had already replaced the spark plugs and ignition coils twice, and it still misfired. The owner suspected carbon build-up on the intake valves and asked us about carbon cleaning.

A misfire is hard to ignore. The engine runs rough, feels hesitant under load, and can trigger the check engine light. Left undiagnosed, it puts strain on the catalytic converter and can lead to a bigger repair bill.

The car

This is a Mercedes-Benz C-Class, the W205 generation, champagne in colour. At about 251,000km on the clock it has done well, but high-mileage engines can develop fuel injector faults over time.

Fuel injectors spray a fine mist of fuel into the engine. Over time, carbon deposits and wear affect how well each injector atomises the fuel, and a failing injector can cause a cylinder to misfire.

How we diagnosed it

We scanned the engine control module. It had two stored misfire codes: P030085, misfire detected, and P030385, a misfire in cylinder 3. Our team confirmed the engine was still misfiring.

The owner had already replaced the spark plugs and ignition coils twice. Our team advised replacing the fuel injectors first, and checking inside the engine if the misfire stayed after that. The owner approved the injector job.

Diagnostic scanner screen showing two stored misfire codes, P030085 and P030385, in the engine control module

Why this happens on a high-mileage C-Class

Fuel injectors work every engine cycle, for the life of the car. At high mileage the internal components wear, and the nozzle tip that sprays the fuel can foul with carbon deposits.

When an injector cannot spray fuel cleanly, the air-fuel mixture in that cylinder becomes uneven. Combustion is incomplete, and the engine control module sees it as a misfire.

What we did

We replaced all four fuel injectors.

Removed all four old fuel injectors.
Fitted four OEM-grade replacement injectors.

The owner then collected the car. Two days later, the owner told us: so far so good, no misfire.

Before and after

Before

Engine misfire at about 251,000km
Spark plugs and ignition coils already replaced twice, misfire still there
Misfire codes P030085 and P030385 stored in the ECM

After

All four fuel injectors replaced
Collected by the owner once the work was done
Owner reported no misfire two days later

Photos from this job

From our team's record of this job. Number plates are pixelated.

What fuel injector replacement costs on a Mercedes in Singapore

The cost depends on the number of injectors replaced and the car model. On this C-Class we replaced all four injectors, quoted as a set.

We quote before any work begins. WhatsApp us your car model and mileage and we will give you an honest figure.

How to avoid a bigger repair

On a direct-injection engine, keeping the fuel system clean helps injectors last longer. Using quality fuel and following the manufacturer's service intervals for fuel system maintenance keeps the injectors in better condition.

The more important step is acting when you first notice a misfire or a check engine light. A misfire that is caught early is usually a smaller repair. One that is ignored for months can damage the catalytic converter, which is a much more expensive part to replace.

If your Mercedes C-Class has high mileage and starts to feel rough, get it scanned with XENTRY before the problem grows.

About the workshop

This Mercedes-Benz C-Class (Fuel injector replacement) was handled at 1 Car Service, an independent workshop in Sin Ming AutoCity, Singapore. For Mercedes-Benz, we use dealer-level XENTRY diagnostics. We hold a 4.9★ rating from 1,836+ Google reviews.

Signs your Mercedes may have a fuel injector fault

Engine running rough or shaking at idle
Hesitation or stumble under acceleration
Check engine light on, especially at high mileage
Increased fuel consumption with no obvious cause
Smell of unburnt fuel from the exhaust
Rough running that gets worse when the engine is cold

Mercedes misfiring? Get it diagnosed properly first.

WhatsApp us your car model and mileage. We plug in XENTRY, find the real fault code, and quote every item before any work starts. Road tested before you collect.

WhatsApp us for honest advice

Mercedes C-Class fuel injector fault: common questions

How much does fuel injector replacement cost on a Mercedes in Singapore?

The cost depends on how many injectors are replaced and the specific model. On high-mileage cars it often makes sense to replace all injectors at once, since they have done the same number of kilometres. We quote before any work begins, so WhatsApp us your model and mileage for an honest figure.

Is it worth replacing fuel injectors on a high-mileage Mercedes C-Class?

Yes, if the rest of the engine is healthy. A fuel injector job restores smooth combustion and protects the catalytic converter, which is far more expensive to replace. On this car at about 251,000km, the owner reported no misfire two days after the new injectors went in. We always confirm what else needs attention before quoting.

How do you diagnose a fuel injector fault on a Mercedes?

We start by reading the fault codes from the engine control module. Misfire codes like the P030085 and P030385 found on this car show that the engine is misfiring, and sometimes on which cylinder, but not why. On this car the spark plugs and ignition coils had already been replaced twice, and our team advised replacing the injectors before looking inside the engine.

Do you use XENTRY for Mercedes diagnostics in Singapore?

Yes. XENTRY is the Mercedes-Benz factory diagnostic system and we use it for Mercedes diagnostics. It reads the same fault codes and live data that a Mercedes dealer uses, so we get the same depth of diagnosis without the dealership bill.

8033 7708 Chat with a specialist

8033 7708

Specialist advice • Honest quote • No obligation