Preliminary Work

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Information

Test conditions for compression pressure check

Engine oil temperature: approx. 80 °C.
Battery voltage: at least 12.5 V.

Remove engine cover. → Removing Engine Cover (Design Cover) 108319 REMOVING AND INSTALLING ENGINE COVER (DESIGN COVER)
Disconnect electric plug connections at the glow plugs.
Disconnect electric plug connection at the fuel pressure regulator -arrow- on the fuel distributor (cylinders 1-3).

Fig 1: Locating Pressure Regulator Electric Plug Connection
Courtesy of PORSCHE CARS NORTH AMERICA, INC.
Reduce the fuel pressure in the fuel distributor.
To do this, start the engine briefly.
Remove all glow plugs.