DELPHI EFI ECU compares input signals to programmed maps in its memory to determine appropriate fuel and spark requirements for immediate operating conditions. ECU then sends output signals to set injector duration and ignition timing. ECU continually performs a diagnostic check of itself, each of sensors, and system performance. If a fault is detected, ECU can turn on a Malfunction Indicator Light (MIL) (if equipped) on equipment control panel, store fault code in its fault memory, and go into a default RSHUDWLQJPRGH'HSHQGLQJRQVLJQLїFDQFHRUVHYHULW\ of fault, normal operation may continue.
A technician can access stored fault code using a blink code diagnosis ADVKHGRXWWKURXJK0,/$QRSWLRQDOFRPSXWHUVRIWZDUH diagnostic program is also available, see Tools and Aids. ECU requires a minimum of 6.0 volts to operate. To prevent engine overspeed and possible failure, a revlimiting feature is programmed into ECU. If maximum RPM limit (4500) is exceeded, ECU suppresses injection VLJQDOVFXWWLQJRIIIXHOARZ7KLVSURFHVVUHSHDWVLWVHOILQ rapid succession, limiting operation to preset maximum. Wiring harness used in EFI system connects electrical components, providing current and ground paths for system to operate.
All input and output signaling occurs through two special all weather connectors that attach and lock to ECU. Connectors are Black and Grey and keyed differently to prevent being attached to ECU incorrectly. Condition of wiring, connectors, and terminal connections is essential to system function and performance. Corrosion, moisture, and poor connections are as likely cause of operating problems and system errors as an actual component. Refer to Electrical System for additional information. EFI system is a 12 VDC negative ground system, designed to operate down to a minimum of 6.0 volts.
If system voltage drops below this level, operation of voltage sensitive components such as ECU, fuel pump, ignition coils, and injectors will be intermittent or disrupted, causing erratic operation or hard starting. A fully charged, 12 volt battery with a minimum of 350 cold cranking amps is important in maintaining steady and reliable system operation. Battery condition and VWDWHRIFKDUJHVKRXOGDOZD\VEHFKHFNHGїUVWZKHQ troubleshooting an operational problem. Keep in mind that EFIrelated problems are often caused by wiring harness or connections. Even small amounts of corrosion or oxidation on terminals can interfere with milliamp currents used in system operation.
Cleaning connectors and grounds will solve problems in many cases. In an emergency situation, simply disconnecting and reconnecting connectors may clean up contacts enough to restore operation, at least temporarily. If a fault code indicates a problem with an electrical component, disconnect ECU connector and test for continuity between component connector terminals and corresponding terminals in ECU connector using an ohmmeter. Little or no resistance should be measured, indicating that wiring of that particular circuit is OK. Crankshaft position sensor is essential to engine RSHUDWLRQFRQVWDQWO\PRQLWRULQJURWDWLRQDQGVSHHG (RPM) of crankshaft.
There are 23 consecutive teeth FDVWLQWRA\ZKHHO2QHWRRWKLVPLVVLQJDQGLVXVHG to reference crankshaft position for ECU. Inductive crankshaft position sensor is mounted 0.200.70 mm LQIURPA\ZKHHO During rotation, an AC voltage pulse is created within sensor for each passing tooth. ECU calculates engine speed from time interval between consecutive pulses. gap from missing tooth creates an interrupted input VLJQDOFRUUHVSRQGLQJWRVSHFLїFFUDQNVKDIWSRVLWLRQQHDU BDC for cylinder #1. This signal serves as a reference for control of ignition timing by ECU. Synchronization of inductive speed pickup and crankshaft position takes SODFHGXULQJїUVWWZRUHYROXWLRQVHDFKWLPHHQJLQHLV started.
Sensor must be properly connected at all times. If sensor becomes disconnected for any reason, engine will quit running. Throttle position sensor (TPS) is used to indicate throttle plate angle to ECU. Since throttle (by way of governor) reacts to engine load, angle of throttle plate is directly related to load on engine. Mounted on throttle body and operated directly off end of throttle shaft, TPS works as a potentiometer, varying voltage signal to ECU in direct correlation to angle of throttle plate. This signal, along with other sensor signals, is processed by ECU and compared to internal preprogrammed maps to determine required fuel and ignition settings for amount of load.
Correct position of TPS is established and set at factory. Do not loosen TPS or alter mounting position unless absolutely required by fault code diagnosis. If TPS is loosened or repositioned, appropriate TPS Learn Procedure must be performed to reestablish baseline relationship between ECU and TPS. Engine (oil) temperature sensor is used by system to help determine fuel requirements for starting (a cold engine needs more fuel than one at or near operating temperature). Mounted in breather cover, it has a temperature VHQVLWLYHUHVLVWRUWKDWH[WHQGVLQWRRLOARZ5HVLVWDQFH changes with oil temperature, altering voltage sent to ECU.
Using a table stored in its memory, ECU FRUUHODWHVYROWDJHGURSWRDVSHFLїFWHPSHUDWXUH8VLQJ fuel delivery maps, ECU then knows how much fuel is required for starting at that temperature. Intake Air Temperature (IAT) sensor is a thermally sensitive resistor that exhibits a change in electrical resistance with a change in its temperature. When sensor is cold, resistance of sensor is high. As sensor warms up, resistance drops and voltage signal increases. From voltage signal, ECU can determine temperature of intake air. Purpose of an air temperature sensor is to help ECU calculate air density. Higher air temperature less dense air becomes.
As air becomes less dense ECU knows WKDWLWQHHGVWROHVVHQIXHOARZWRDFKLHYHFRUUHFWDLUIXHO ratio. If fuel ratio was not changed engine would become rich, possibly losing power and consuming more fuel. Oxygen sensor functions like a small battery, generating a voltage signal to ECU based upon difference in oxygen content between exhaust gas and ambient air. 24 KohlerEngines.com 24 690 01 Rev. D