Alfa Giulietta Power Loss & Knocking: Diesel Trouble

I had a very similar issue with my 2011 Alfa Giulia diesel. Having some experience with diesel engines, those symptoms immediately caught my attention since they match what I encountered. In my case, the reduced power and increased fuel consumption were actually symptoms of a clogged intake manifold, a problem that developed because of a faulty turbocharger seal. The turbocharger was leaking oil, which accumulated in the intake system over time. The good news was that since the turbocharger issue was covered under an extended warranty campaign, the repair, including cleaning the intake manifold, was completely free. The workshop diagnosed it using pressure testing and visual inspection of the intake system. Before I can provide more specific advice, could you share: Current mileage on your Giulietta? Are you getting any specific error codes? Does the knocking sound change with engine speed? When was your last timing belt service? These details would help determine if your situation matches what I experienced. The crankshaft sensor readings during diagnosis were also crucial in my case, so that might be worth checking.

Thanks for sharing your experience. Just had my car serviced at 84348 KM where they also found similar issues with engine knocking. The mechanic diagnosed worn piston rings causing compression loss, which explained the power reduction and excessive fuel usage. The camshaft and timing belt were inspected and thankfully those components were fine. However, the intake manifold showed significant carbon buildup that needed cleaning. Our symptoms do sound quite similar, especially regarding the reduced power and engine performance issues. Based on what you described about the turbo seal, I will definitely have that checked as well since it could be contributing to my problems. Did your mechanic mention how long it took to complete the full repair?

The full repair in my case took about 3 working days, mainly because we had to wait for the turbocharger parts to arrive. The actual work of replacing the turbocharger seals and cleaning the intake system was completed in about 8 hours of labor. Interesting that your mechanic found worn piston rings, that definitely explains the compression issues. In my situation, they initially suspected piston rings too, but compression testing revealed the turbocharger was the primary culprit. The carbon buildup you mentioned is a common issue when oil leaks past worn turbo seals, creating a cycle of problems. Since your symptoms match mine so closely, I would strongly suggest having them check the head gasket too while they are working on it. A failing head gasket can sometimes show similar symptoms, and its much more cost effective to address everything at once while the engine is partially dismantled. The spark plug readings in my case also showed oil fouling, which was another indicator of the turbocharger seal issue. Did your mechanic mention anything about the condition of your plugs during the service?

Thanks for all the detailed feedback. The repair estimates came in today, looking at 2200 Euro for the full job including both the piston rings and turbocharger seal replacement. The head gasket thankfully tested fine, so we can skip that for now. The spark plugs were indeed quite fouled with oil residue, just as you mentioned. The mechanic says the engine knocking should completely resolve once the piston rings are replaced and the intake manifold is properly cleaned. They quoted 4-5 days total for the complete repair. Going to schedule it for next week. Really appreciate everyone sharing their experiences, helped me better understand the issue and know what questions to ask at the shop. Will post an update once everything is fixed to share how it turned out.