Isuzu 4HK-1, Manual, Page: 8 / 50

8
Isuzu 4HK-1 and 6HK-1 Engine Overview (continued)
Inputs to 81 pin engine harness connector:
•
The 2 wire intake air temperature (IAT) sensor is installed on intake air tube and
detects the temperature of intake air for optimum fuel injection control.
•
The 2 wire boost temperature sensor is installed onto the EGR valve on the
upstream side of intake manifold. The sensor is a thermistor type. The resistance in
the sensor changes as the temperature changes. When the intake temperature
sensor is cold, the sensor resistance is high. When the intake temperature
increases, the sensor resistance decreases. With high sensor resistance, the ECM
detects a high voltage on the signal circuit. With lower sensor resistance, the ECM
detects a lower voltage on the signal circuit.
•
The 3 wire barometric pressure sensor is installed on the machine and converts the
ambient barometric pressure into a voltage signal. The ECM calculates barometric
pressure by this voltage signal and corrects the fuel injection amount (high-altitude
correction) as the machine works at a higher elevation.
•
The 3 wire engine oil pressure sensor is located on the left side of the engine just
below and forward of the high pressure injection pump.
•
An engine emergency stop signal is sent from the machine controller to the engine
controller. The machine controller receives an engine stop signal from the stop
switch located in the instrument cluster.
•
As the engine is started (after the key switch is turned to the START position to start
the engine, and until the return of the key switch to the ON position), optimum fuel
injection quantity is delivered based on information from the starter switch signal,
engine speed, and the engine coolant temperature sensor (ECT). At low
temperature, the fuel injection quantity increases. As the engine starts completely,
this boosted quantity mode at starting is cancelled and normal running mode is
restored.
•
Power Supply – Ignition power is sent to the engine control module (ECM) any time
that the key switch is in the run position. When the ignition signal is present, the
ECM activates the main relay. Once the Main Relay (K33 on machine schematic) is
activated, battery power is fed to the ECM through the relay normally open (NO)
contact to pins number 2 and 6. When the key switch is turned to the off position,
the ECM continues to hold the main relay activated for a period of time to allow the
ECM to power down safely. This delay is about 10 seconds. The ECM has six
ground connections in total.