VW Polo Diesel Performance Drop Due to Cylinder Issues

Had a similar situation with my 2016 VW Golf TDI. The symptoms matched exactly, poor performance, increased fuel consumption, and rough running. Initially thought it was a fuel injector problem, but diagnostic testing revealed a more complex issue. The root cause turned out to be carbon buildup affecting the cylinder pressure, which damaged one fuel injector and created a chain reaction of problems. The turbocharger was also affected due to inconsistent pressure in the system. The repair required: Cleaning carbon deposits, Replacing damaged fuel injector, Recalibrating injection timing, Testing turbocharger function, Adjusting cylinder pressure This was a serious repair job that took several days to complete properly. The symptoms you describe strongly suggest fuel delivery issues, possibly stemming from carbon buildup like in my case. Would recommend getting a second opinion from a shop specialized in VW diesel engines, as these issues can worsen and cause additional damage if left unaddressed. Important to note that with diesel engines, cylinder pressure problems often indicate upstream issues with the fuel injection system. A proper diagnosis should include fuel pressure testing and injector spray pattern analysis.

Really appreciate you sharing that experience, very similar to what I dealt with in my Polo last year. The carbon buildup issue makes a lot of sense given my symptoms. Just got the car back today actually, they found a faulty fuel injector that needed replacement plus some carbon cleaning too. By chance do you remember roughly what you paid for the full repair? Also wondering if youve had any other problems since getting it fixed? My mechanic mentioned something about checking the head gasket next service just to be safe.

The repair cost on my Golf came to 0€ since it was covered under warranty as a consequential issue from a previous repair. Pretty fortunate timing on that. Since getting the cylinder pressure fluctuation fixed, the car has been running perfectly. The engine idles smoothly, fuel economy is back to normal, and performance is exactly where it should be. The mechanic did a thorough job checking the intake manifold and timing belt while they had everything apart, which likely helped prevent future issues. Regarding the head gasket inspection your mechanic mentioned, that is smart preventative maintenance. Head gasket problems can develop from prolonged pressure irregularities, though I have not experienced any issues with mine in the years since the repair. The turbocharger and surrounding components have also remained in good condition, likely because the root cause was addressed before it could cause widespread damage.

Thanks for the input. Finally got the car back from the shop yesterday after a week-long ordeal. The diagnostic revealed exactly what was discussed, bad fuel injector and carbon deposits causing the rough running and power loss. Total bill came to 850€ for parts and labor. The mechanic did a full fuel system cleaning and replaced two faulty injectors that were causing uneven cylinder pressure. They also inspected the turbocharger which thankfully showed no damage. The engine knocking has completely disappeared and it runs like new again. Had a bit of a scare when the camshaft position sensor threw a code during testing, but it turned out to be just a loose connection they fixed at no extra charge. Really glad I got it sorted before any major damage occurred. No issues since picking it up, fuel economy is back to normal and power delivery is smooth. Definitely learned my lesson about getting strange engine symptoms checked out promptly rather than hoping they go away on their own. Will be following up at the next service to make sure everything is still running properly.