Misfire: Comprehensive Checks

[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

Edited January 10, 2016 by Joseph Stone

[Loren]

:welcome: 

 

In modern OBD II cars fault codes usually tell you more than you need to know to solve most problems.

Without the fault codes - everything is just guess and potentially an endless stream of wasted money.

Have your fault codes read with either a Porsche diagnostic tool (PIWIS) or Durametric (Porsche specific) software - then report your fault codes back here.

 

We can give you specific factory procedural tests for most all faults.