Grand Marquis V8-4.6L Flex Fuel (2010)
Compression Check: Testing and Inspection
Compression Test
Engine
Component Tests
The following component tests are used to diagnose engine concerns.
Compression Test
WARNING: Before servicing a vehicle equipped with a fire suppression system, depower the system by following the procedure in Vehicle
Jacking and Lifting. Failure to follow the instructions may result in serious personal injury.
1. Make sure the oil in the crankcase is of the correct viscosity and at the correct level and that the battery is correctly charged. Operate the vehicle
until the engine is at normal operating temperature. Turn the ignition switch to the OFF position, then remove all the spark plugs.
2. Set the throttle plates in the wide-OPEN position.
3. Install a compression gauge such as the Compression Tester in the No. 1 cylinder.
4. Install an auxiliary starter switch in the starting circuit. With the ignition switch in the OFF position, and using the auxiliary starter switch, crank
the engine a minimum of 5 compression strokes and record the highest reading. Note the approximate number of compression strokes necessary to
obtain the highest reading.
5. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
6. WARNING: If the vehicle is equipped with a fire suppression system, repower the system. For important safety warnings and
procedures, refer to Vehicle Jacking and Lifting. Failure to follow these instructions may result in serious personal injury.
If equipped with a fire suppression system, repower the system.
Compression Test - Test Results
The indicated compression pressures are considered within specification if the lowest reading cylinder is at least 75% of the highest reading. Refer to the
Compression Pressure Limit Chart.
Compression Pressure Limit Chart
