Joseph Stone

Hello, I have a 2010 Porsche Cayenne S. I have had recurring cylinder misfire problems. I am writing here to ask for advice and hopefully provide guidance for any other people with similar problems. Question: Would a good independent mechanic that works on Porsches have all the tools to detect the source of the problem or should I go to the dealer? Do you have any advice on what I should ask them to do? What cost should I expect for the checks (excluding repairs)? Problem: 2010 Porsche Cayenne S with 45000 miles on it. After I changed spark plugs at 40k as a recommended service, cylinder 3 had a misfire. The independent mechanic changed the coil. He said electrical problems are generally isolated and most likely that individual coil is the only one with problems. What I found surprising is that he didn't have any tools to check whether the coil was malfunctioning. He just assumed the coil was the problem. Later I had a misfire at cylinder 5 that would go and come back. The Porsche dealer changed the coil on cylinder 5. After 300 miles, the cylinder 5 has another misfire. I would like to get to the bottom of this. I have read through many forums and websites. Here are the recommended checks if you have an engine misfire. If anyone would like to comment about them or tell us how much they cost or how useful they would be, it might be helpful as well. I don't know what some of these items mean, so I would welcome any corrections as well. Replace spark plugs Switch/Replace/Disconnect coils and see if the problem moves/disappears/stays the same Check if the spark plugs are fouled (oil or carbon fouled) Switch Petrol injectors Check Fuel Pumps Check for fuel leaks around the injectors and fuel rail Replace Inlet Manifold Gaskets Valve Issues Schrader Valve Leaks Clean Cam Sensors Compression Test Borescope check - Scored Cylinder Borescope Check - Scored Cylinder #5 problem on Cayennes Many thanks, Added Note: CEL Light Error Code for the last two times were P0305