Compression Sense Ignition (CSI)

The 2.2 liter engine utilizes Compression Sense Ignition, which eliminates the need for a camshaft position sensor. The EI module has sensing circuitry that detects when cylinder # 1 or cylinder # 3 has fired on its compression stroke and relays this information to the ECM. The ECM can then correctly synchronize the fuel injectors for sequential fuel injection. If the ECM cannot detect a correct cam signal, it will default to using the Alternating Synchronous Double Fire (ASDF) method to inject fuel.

The EI module uses capacitive pickup plates located above the 1/4 and 2/3 coils to determine when cylinder # 1 or cylinder # 3 has fired on compression. These plates are used to differentiate the polarity and voltage amplitude difference between the # 1 and # 4 or # 2 and # 3 secondary ignition circuits. Since each coil tower is of opposite polarity and the waste spark (2-4 kV) generally fires before the compression spark (10-25 kV), the module can determine when cylinder # 1 or # 3 is on compression. When the EI module detects a positive to negative polarity sequence and a high negative voltage spike, it will supply 5 volts to the ECM on the cam signal circuit. The ECM knows which cylinder has just fired on its compression stroke when this transition occurs.

The EI module, however, cannot always detect when cylinder # 1 or # 3 has fired on compression. These occurrences include:
^ During deceleration
^ Very low engine load conditions when engine is running
^ If a primary/secondary ignition problem occurs

The Scan tool displays the cam signal to the ECM as CALC. COMPRESSION OUTPUT. Since the engine firing order is 3-4-2-1, a normal compression output bit pattern will be 00000110 or 00001001 during engine crank, idle, cruise or accel. If a fault is occurring in the ignition system or if a cylinder is loosing compression, the bit pattern will intermittently change or stray from the normal pattern. This bit pattern can be used to determine the cause of a misfire. Refer to DTC P0300 for different bit patterns vs. a specific failure mode.