MI-04 Ignition management In the normal course of events, with the engine operating at the correct temperature in defined conditions, the SECM will use load and engine speed to derive the correct ignition timing. In addition to load and speed there are other circumstances under which the SECM may need to vary the ignition timing, including low engine coolant temperature, air temperature, start-up, idle speed control. VR Sensor (1) Timing Wheel (2) VR Sensor A Variable Reluctance sensor (Figure 31) is an electromagnetic device consisting of a permanent magnet surrounded by a winding of wire. The sensor is used in conjunction with a ferrous timing wheel located on the crankshaft pulley.
The timing wheel is referred to as 30-5 ignition because the wheel has 30 gear teeth with 5 removed at precise locations, giving the SECM a very accurate speed reference signal. Rotation of the timing wheel near the tip of the sensor changes the magnetic flux, creating an analog voltage signal in the sensor coil. Ignition Coil (Smart Coil) The MI-04 system is capable of operating with either a distributor based ignition system or a distributor less ignition system. The current application uses a distributor based ignition system. The distributor will have no internal advance mechanisms giving the SECM consistent authority over ignition timing.
The spark is sent to the appropriate cylinder in the conventional way via the rotor arm and spark plug wires. The SECM uses the signal from the VR (Variable Reluctance) sensor mounted near the crankshaft pulley to determine the engine position and RPM at any time. It uses this information together with the information from the TPS sensor and TMAP to calculate the appropriate ignition timing settings for the “smart coil”. The MI-04 system uses a single coil, which incorporates the ignition driver circuitry inside the coil itself. The SECM signals the “smart coil” when to begin its dwell cycle then the coil waits for the trigger signal from the SECM.
The “smart coil” eliminates the need for a driver circuit inside the SECM or externally from the coil. Using a single VR sensor and “smart coil” eliminates multiple sensors and coil packs used in more complex ignition systems. Distributor The distributor of G420/G424 engine has the mechanical advance system internally. But the new distributor of G420E/G424E engine has no internal advance mechanisms. A333011: Distributor assy for G420E/G424E engines A218350: Distributor assy for G420/G424 engines “SmartCoil” 1 2 Figure 31 G420E/G424E Tier LP Engine System Operational Overview 29