NOTE: The powertrain control module (PCM) receives an error message when the fuel pump relay is removed or electrical components are disconnected. This error message must be deleted from the fault memory using the Ford diagnostic equipment after completing the compression test. NOTE: Valve clearance must be set correctly before performing a compression test. Make sure the engine is at the normal operating temperature. NOTE: The varying design of compression checking devices and fluctuating starter motor speeds normally only allows for a comparison to be made of the compression pressures in all cylinders.