17/05/2026
Mercedes GLA220d OM651 came in with intake flap faults, rough running and intermittent injector-related issues.
Initial diagnosis pointed toward the intake manifold/swirl flap system as this was the main persistent fault stored in the ECU, so the investigation started there.
During strip-down and further testing, the engine condition deteriorated significantly with: • Heavy juddering
• White smoke
• Raw diesel from exhaust
• Fuel dilution in engine oil
• Unstable cylinder balance values
Live data initially pointed in multiple directions, with injector corrections constantly shifting between cylinders. Leak-off test was good, which made diagnosis more interesting than a typical failed injector.
After deeper testing and monitoring live smooth-running data, injectors were removed and sent for bench testing.
Results: • Injector 4 leaking badly
• Other injectors had badly burnt nozzles
• Fuel was washing into the oil and exhaust system
Injectors repaired/refitted, fresh oil and filter fitted, adaptations reset and now running perfectly smooth again with injector corrections sitting around ±2.
Another reminder that injector faults on these OM651 engines can imitate timing issues, chain stretch and other major mechanical faults.
Good result in the end 👌🔧
