Coolant Temperature Sensors
There are 3 components which supply coolant temperature information to the MCU. They are the coolant temperature switch, coolant temperature sensor and the thermotimer. All 3 devices are located in the water jacket of the engine block. They supply coolant temperature information to the MCU in the form of electrical signals.
The MCU interprets these signals as cold or normal operating temperatures. During cold operating conditions, the air/fuel mixture is enriched by the cold start valve. This valve is located in the intake manifold, downstream from the butterfly valve. It supplies additional fuel to the inlet charge when signaled by the MCU. Extra rich conditions are maintained until normal operating temperature is reached.
MOTRONIC SYSTEM TROUBLE SHOOTING CHART
| Condition | Possible Cause |
|---|---|
| Cold Engine Will Not Start | Fuel Pressure, Fuel Injector, Cold Start Valve, Speed Transmitter, Reference mark Transmitter, Air Flow Sensor, Wire Connections and Plugs, Ignition Coil |
| Cold Engine Starts, But Stalls | Fuel Injector, Motronic Control Unit, Cold Start Injector, High Voltage Distributor, Spark Plugs, Temp. Time Switch |
| Warm Engine Will Not Start | Fuel Pressure, Fuel Injector-Motronic Control Unit, Speed Transmitter, Reference Mark Transmitter, Wire Connections and Plugs, Ignition Coil, Secondary Air of Engine |
| Erratic Idle/Warm-Up Phase | Throttle Switch, Coolant Temp. Sensor, Idle Valve, Motronic Control Unit, Idle Control Unit, Throttle Switch, Air Temp. Sensor, Temp. Switch 112° (45°C), Wire Connections and Plugs, High Voltage Distributor, Spark Plugs, Ignition Circuit, Intake System, Coolant |
| Engine Backfiring | Fuel Injector, Motronic Unit, High Voltage Distributor, Spark Plugs, Ignition Circuit, Exhaust System |
| Idle Speed Incorrect | Fuel Injector, Cold Start Injector, Motronic Control Unit, Intake System, Throttle Switch, Temp. Time Switch, Coolant Voltage Distributor |
| Acceleration Hesitation | Fuel Injector, Motronic Control Unit, Wire Connections, High Voltage Distributor, Spark Plugs, Ignition Circuit |
| Acceleration Knock | Motronic Control Unit, Wire Connections, Spark Plugs, Ignition Coils |
| Coasting Hesitation | Fuel Injector, Motronic Control Unit, Wire Connections and Plugs |
| Engine Misfiring All Conditions | Fuel Injector, Motronic Control Unit, Wire Connections and Plugs, Ignition Circuit, Intake System, Exhaust System, Secondary Air of Engine, Coolant, Insufficient Engine Power, Fuel Injector, Fuel Pressure, Motronic Control Unit, Air Flow Sensor, Throttle Sensor, Coolant Temp. Sensor, Air Temp. Sensor, Ignition Circuit, Intake and Exhaust System |
| High Fuel Consumption | Fuel Injector, Cold Start Injector, Motronic Control Unit, Throttle Switch, Temp. Time Sensor |
| CO Level Incorrect | Fuel Injector, Cold Start Injector, Oxygen Sensor, Wire Connections and plugs, Intake System, Secondary Air of Engine |
| HC and NO(x) Excessive | Fuel Injector, Cold Start Injector, Motronic Control Unit, Oxygen Sensor, Wire Connections and Plugs, Intake System, Secondary Air of Engine |