- Review the system operation in order to familiarize yourself with the system functions. As required, disable the auto-stop function prior to repair. Refer to Hybrid Modes of Operation Description.
- Ignition key in the OFF position.
- Charge the battery if the battery is not fully charged.
- Disable the fuel and spark by removing the Fuel Pump relay and Powertrain relay. Refer to Electrical Center Identification Views for the Fuse Block - Underhood Label.
- Remove the spark plug wires from the spark plugs.
- Remove all of the spark plugs.
- Install a compression gage to the cylinder to be tested.
- Start with the compression gage at zero and crank the engine 3-5 seconds using the ignition key.
- Return the ignition key to the OFF position.
- Measure the compression for each cylinder. Record the readings.
- The minimum compression in any 1 cylinder should not be less than 70 percent of the highest cylinder. For example, if the highest pressure in any 1 cylinder is 862 kPa (125 psi), the lowest allowable pressure for any other cylinder would be 607 kPa (88 psi). (862 kPa x 70% = 607 kPa) (125 psi x 70% = 88 psi).
- If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole. Measure the compression again and record the reading.
- Reinstall the Fuel Pump relay and Powertrain relay.
- Using the scan tool, clear all diagnostic codes.
Warning: Do not leave the ignition key in the ON position after the test is performed. Leaving the key in the ON position may result in an Auto-Start of the engine and possible personal injury.
Note: When performing an engine cylinder compression test for the RPO-LFA engine, note that this engine has a camshaft position actuator with a late intake valve closing feature and a 29 degree retard park position. With the actuator parked in a retard position, the effective compression of the engine is reduced during cranking. Compression values on the gage will be lower than a typical small block engine that does not have this feature.
Warning: Do not leave the ignition key in the ON position after the test is performed. Leaving the key in the ON position may result in an Auto-Start of the engine and possible personal injury.
| • | Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder. |
| • | Piston Rings Leaking -- Compression is low on the first stroke. Compression builds up with the following strokes, but does not reach normal. Compression improves considerably when you add oil. |
| • | Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil. |
| • | If 2 adjacent cylinders have lower than normal compression, and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders. |
