A7 Diesel Performance Drop with High Fuel Usage

Had similar symptoms with my 2013 Audi A6 3.0 TDI. The engine knocking and poor performance turned out to be a serious issue, failed head gasket causing loss of compression in two cylinders. The initial signs matched yours: increased fuel consumption, sluggish acceleration, and check engine light. Even though the turbocharger and fuel injectors were good, cylinder pressure kept dropping. A compression test revealed the root cause. These symptoms often get misdiagnosed as intake manifold or fuel system problems. The head gasket failure was actually caused by a previous repair where the torque settings were incorrect during reassembly. Required complete cylinder head removal and machining. Key checks needed: Full compression test across all cylinders, Leak-down test, Coolant pressure test, Oil analysis for combustion gases The repair was major, requiring engine teardown. Would recommend finding a specialist with documented experience on VAG diesel engines, as proper diagnosis and repair sequence is critical. The spark plug wells should also be checked for oil seepage, as this can indicate additional gasket issues around the valve cover area.

Thanks for sharing your A6 experience. Your symptoms do sound identical to what I experienced with my A7. After reading your detailed breakdown, Im fairly certain my head gasket could be the culprit too, especially since the compression issues point that way. Quick question, do you remember roughly what the total repair cost was for your case? Also curious if youve had any related problems pop up since the head gasket replacement? Mine also has that knocking sound you mentioned, and Im trying to decide if I should take it to a shop that specializes in crankshaft and camshaft repairs, given how deep they might need to go into the engine.

After getting it properly diagnosed, my total repair ended up being covered under warranty since the head gasket failure was traced back to incorrect torque settings from a previous repair. The shop acknowledged their mistake with the initial work on the camshaft, which had caused the cylinder pressure fluctuations. Since the head gasket replacement, the engine has run perfectly, no knocking sounds, proper compression, and fuel consumption back to normal. The piston rings were also inspected during the repair and showed no wear, which was a relief. For your A7, definitely go with a specialist shop that has experience with these engines. The connection between crankshaft, camshaft, and head gasket integrity is crucial. Even though my repair cost was 0 Euro due to the warranty coverage, these jobs typically require significant labor hours since they need to access deep engine components. The most important thing is getting an accurate diagnosis first through compression testing, as head gasket issues can sometimes be confused with other problems like failing fuel injectors.

I took my A7 to a specialist shop yesterday after reading about your similar experience. The diagnostic tests confirmed what I suspected, its definitely the head gasket. The compression test showed uneven readings across cylinders, matching exactly what you described. The mechanic found coolant traces where it shouldnt be and immediately spotted the connection to the head gasket failure. They also checked the intake manifold and spark plug wells while the engine was open, finding some minor wear but nothing serious. The full repair is scheduled for next week. Looking at around 2800 Euro for parts and labor, including machining the cylinder head. They mentioned checking the crankshaft and camshaft alignment during reassembly to prevent future issues. While its not great news, Im relieved to finally have a clear diagnosis. Thanks again for sharing your experience, it helped me push for the right tests and avoid potentially incorrect repairs. Hoping this fixes the fuel consumption and performance issues completely.