Compression Check: Testing and Inspection
AllData Editors Note - Ford does not provide a cranking pressure specification, only an acceptable range.General Remarks
Note: Removing fuses and disconnecting electrical components causes the powertrain control module (PCM) to come up with an error message. After measurement has been carried out this error message should be cleared from memory by connecting NGS.
Note: Only check the compression pressure with the valves set to the prescribed clearance (if this can be adjusted).
The compression pressure should be checked with the engine at operating temperature.
Differing designs of compressor pressure recorder and varying starter motor speeds usually only make it possible to check that the compression is the same in all cylinders.
Check The Compression Pressure-2.0L
Warning: On manual transaxles shift the transaxle into neutral. On automatic transaxles select "P". Failure to follow this instructions will result in personal injury.
1. Open the Central Junction Box (CJB).
2. Remove the Fuel Pump Relay (R8).
3. Stan the engine-the engine will start up, run for a few seconds and then stall.
4. Remove the cover plate from the cylinder head cover.
5. Remove the spark plugs.
6. Pull off the spark plug connectors.
7. Pull off the ignition coil electrical connector.
8. Install auxiliary starter switch in starting circuit. With ignition switch OFF, using auxiliary starter switch, crank engine a minimum of five compression strokes and record the highest reading. Note the approximate number of compression strokes required to obtain the highest reading.
9. Repeat test on each cylinder, cranking the engine approximately the same number of compression strokes.
10. Install the components in the reverse order, observing the specified tightening torques.
11. Reset the PCM fault memory.
Check The Compression Pressure-2.5L
Warning: On manual transaxle shift the transaxle into neutral. On automatic transaxles select "P". Failure to follow this instructions will result in personal injury.
1. Open the Central Junction Box (CJB).
2. Remove the fuel pump relay (R8).
3. Start the engine. The engine will start up, run for a few seconds and then stall.
4. Remove the engine cover.
5. Pull off the spark plug wires and remove the spark plugs.
6. Disconnect the electrical connector from the coil.
7. Install auxiliary starter switch in starting circuit. Within ignition switch OFF, using auxiliary starter switch, crank engine a minimum of five compression strokes and record the highest reading. Note the approximate number of compression strokes required to obtain the highest reading.
8. Repeat test on each cylinder, cranking the engine approximately the same number of compression strokes.
9. Install the components in the reverse order, observing the specified tightening torques.
10. Reset the PCM fault memory.
Interpretation Of The Results
The indicated compression pressure are considered within specification if the lowest reading cylinder is within 75 '7o of the highest reading.
Caution: If engine oil is sprayed into the combustion chamber, after carrying out the measurement run the engine at 2000 rpm for about 15 minutes, in order to burn the oil and prevent damage to the catalytic converter.
If the measurement on one or more cylinders is much lower than the specified value, spray some engine oil into the combustion chamber and repeat the compression measurement.
If the reading greatly improves then the piston rings are damaged.
If the reading stays the same then the cause is either bad valve seats or valve stem seals.
If the measurements for two cylinders next to each other are both too low then it is very likely that the cylinder head gasket between them is burnt through. This can also be recognized by traces of engine oil in the coolant and/or coolant in the engine oil.