A 2014 Mercedes-Benz CLA220 AMG 2.1 diesel was booked in recently, with the customer complaining about a lack of power. There was also a fairly lengthy story about recent work done to the car. The vehicle had been booked into another garage locally for the same complaint. This somehow led to the DPF internals being removed and the software modified to delete the DPF system from the vehicle. This was done without the customer being told, and they had not authorised the work. When the vehicle was handed back it was no better, and the customer returned to the garage. It was at this point they learned about what had been done and quite rightly they were not impressed. The car was then taken to another garage which installed a functioning second-hand DPF, corrected the software back to standard and also corrected a few other issues including a seized exhaust flap. However, the car still exhibited a lack of power and clearly didn’t have the AMG get-up-and-go it left the factory with. It was at this point the vehicle was brought to me. Initial inspection As can be seen in Fig.1, upon initial inspection we had two fault codes. The first was for the boost pressure deviating from the specified value. According to the sub code of 71, this indicated the actuator was blocked. At this point I wasn’t sure if the turbo had an electronic actuator or used a vacuum/pressure waste gate but this code clearly could cause the issues as explained by the customer. The second fault code indicated a learning value for the injector on cylinder 2 to be at its lower limit. This could also cause a lack of power complaint or limp home to be activated. This meant I had some good diagnostic direction to create a test plan and start doing some checks to locate the problem. I then drove the vehicle with live data displayed to look at boost data and injector data while also confirming the customer’s complaint at the same time. The vehicle was indeed low on power and felt flat, not what you would expect from a 2.1 litre turbo-charged engine. However, injector information looked okay and the boost levels reached where I expected them to. This included the turbo actuator position changing in relation to engine RPM and demand. The only points to note were that there was only actual boost in data and I could not see what the control unit was looking to see. It also felt too slow for the build in boost to happen and not as instant as it is usually with a modern diesel engine. Turbo waste gate Returning to the workshop, I decided to look into how the turbo waste gate was controlled to make sure it was functioning correctly. On this engine the actuator is electrically controlled by the engine control unit, also incorporating a position sensor for feedback to the ECU. The scan tool listed an actuator test moving the actuator arm from 5 and 90% travel. So, I decided my plan would be to test the actuator for correct operation and make sure the turbo control arm moved by the waste gate was free and had full travel. If this is stiff or seized then the actuator will struggle to move it. If all was ok, I would then verify the plausibility of the pressure sensors and also check the injector correction factors to see if an issue could be seen with the injector on cylinder 2, compared to the other three which didn’t log any faults. Carrying out the actuator test, the arm moved freely both from 5 to 90% travel. However, there was not much of a difference in terms of travel between the two positions. With 26 AFTERMARKET MAY 2023 TECHNICAL www.aftermarketonline.net TRAVELLING WITHOUT MOVING? A Merc tested Neil to the max recently and at times just did not make sense but perseverance and a solid test plan got him the fix in the end BY Neil Currie
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