Preliminary Work

WARNING: This page is about a different car, the 2010 Porsche Cayenne, 2009 Porsche Cayenne, and 2008 Porsche Cayenne. However, it is still accessible from the selected car via links, so may be relevant.

Unscrew all spark plugs. → WM 287020 REMOVING AND INSTALLING SPARK PLUGS ON DFI ENGINES
Position cylinder to be tested to ignition TDC and remove tool (dead centre finder).
1. 2.1. The dead centre finder or "cylinder pipe" consists of a glass tube (inspection glass) with a piston -1- , hose and a rubber cone -2- .
  
  Fig 1: Identifying Dead Centre Finder - Cylinder Pipe
  Courtesy of PORSCHE CARS NORTH AMERICA, INC.
2. 2.2. The rubber cone is pressed onto the spark plug hole. The inspection glass is either held by a helper or is secured vertically in a clearly visible position with a magnet.
  
  Fig 2: Setting Tool For Dead Centre Finder
  Courtesy of PORSCHE CARS NORTH AMERICA, INC.
3. 2.3. If the engine is now turned in direction of rotation on the crankshaft, the piston in the inspection glass is pressed up in the compression cycle in order to go back down immediately upon reaching the TDC. The piston in the inspection glass stays down in overlapping TDC →
  
  Fig 3: Identifying Piston Up
  Courtesy of PORSCHE CARS NORTH AMERICA, INC.
  
  Fig 4: Identifying Piston Down
  Courtesy of PORSCHE CARS NORTH AMERICA, INC.