Fuel Injection System
SYSTEM OPERATIONAll engines used have a sequential Multi-Port Electronic Fuel Injection system. The MPI system is computer regulated and provides precise air/fuel ratios for all driving conditions. The Powertrain Control Module (PCM) operates the fuel injection system.
The PCM regulates:
- Ignition timing
- Air/fuel ratio
- Emission control devices
- Cooling fan
- Charging system
- Idle speed
- Vehicle speed control
Various sensors provide the inputs necessary for the PCM to correctly operate these systems. In addition to the sensors, various switches also provide inputs to the PCM.
All inputs to the PCM are converted into signals. The PCM can adapt its programming to meet changing operating conditions.
Fuel is injected into the intake port above the intake valve in precise metered amounts through electrically operated injectors. The PCM fires the injectors in a specific sequence. Under most operating conditions, the PCM maintains an air fuel ratio of 14.7 parts air to 1 part fuel by constantly adjusting injector pulse width. Injector pulse width is the length of time the injector is open.
The PCM adjusts injector pulse width by opening and closing the ground path to the injector. Engine RPM (speed) and manifold absolute pressure (air density) are the primary inputs that determine injector pulse width.
PCM REPLACEMENT
USE THE DRB SCAN TOOL TO REPROGRAM THE NEW PCM WITH THE VEHICLES ORIGINAL IDENTIFICATION NUMBER (VIN) AND THE VEHICLES ORIGINAL MILEAGE. IF THIS STEP IS NOT DONE A DIAGNOSTIC TROUBLE CODE (DTC) MAY BE SET.
Modes of operation
As input signals to the PCM change, the PCM adjusts its response to output devices. For example, the PCM must calculate a different injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT). There are several different modes of operation that determine how the PCM responds to the various input signals.
There are two different areas of operation, OPEN LOOP and CLOSED LOOP. During OPEN LOOP modes the PCM receives input signals and responds according to preset PCM programming. Input from the oxygen (O2S) sensor is not monitored during OPEN LOOP modes.
During CLOSED LOOP modes the PCM does monitor the O2S sensor input. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air/fuel ratio of 14.7 parts air to 1 part fuel. By monitoring the exhaust oxygen content through the 02S sensor, the PCM can fine tune the injector pulse width. Fine tuning injector pulse width allows the PCM to achieve optimum fuel economy combined with low emissions.
The multi-port fuel injection system has the following modes of operation:
- Ignition switch ON (zero RPM)
- Engine start-up
- Engine warm-up
- Cruise (Idle)
- Acceleration
- Deceleration
- Wide Open Throttle
- Ignition switch OFF
The engine start-up (crank), engine warm-up, and wide open throttle modes are OPEN LOOP modes. Under most operating conditions, the acceleration, deceleration, and cruise modes, with the engine at operating temperature are CLOSED LOOP modes.
Ignition Switch ON (Zero RPM) Mode
When the multi-port fuel injection system is activated by the ignition switch, the following actions occur:
- The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.
- The PCM monitors the coolant temperature sensor and throttle position sensor input. The PCM modifies fuel strategy based on this input.
When the key is in the ON position and the engine is not running (zero rpm), the Automatic Shutdown (ASD) relay and fuel pump relay are not energized. Therefore battery voltage is not supplied to the fuel pump, ignition coil, fuel injectors or oxygen sensor heating element.
Engine Start-up Mode
This is an OPEN LOOP mode. The following actions occur when the starter motor is engaged.
If the PCM receives the camshaft position sensor and crankshaft position sensor signals, it energizes the ASD relay and fuel pump relay. These relays supply battery voltage to the fuel pump, fuel injectors, ignition coil, and oxygen sensor heating element. If the PCM does not receive the camshaft position sensor and crankshaft position sensor signals within approximately one second, it de-energizes the ASD relay and fuel pump relay.
The PCM energizes all injectors until it determines crankshaft position from the camshaft position sensor and crankshaft position sensor signals. The PCM determines crankshaft position within 1 engine revolution.
After determining crankshaft position, the PCM begins energizing the injectors in sequence. The PCM adjusts injector pulse width and controls injector synchronization by turning the individual ground paths to the injectors On and Off.
When the engine idles within ± 64 RPM of its target RPM, the PCM compares current MAP sensor value with the atmospheric pressure value received during the Ignition Switch On (zero RPM) mode. If the PCM does not detect a minimum difference between the two values, it sets a MAP diagnostic trouble code into memory.
Once the ASD and fuel pump relays have been energized, the PCM:
- Determines injector pulse width based on engine coolant temperature, MAP and the number of engine revolutions since cranking was initiated.
- Monitors the engine coolant temperature sensor, camshaft position sensor, crankshaft position sensor, MAP sensor, and throttle position sensor to determine correct ignition timing.
Engine Warm-up Mode
This is a OPEN LOOP mode. The following inputs are received by the PCM:
- Engine coolant temperature
- Manifold absolute pressure
- Engine speed (crankshaft position sensor)
- Throttle position
- A/C switch
- Battery voltage
The PCM adjusts injector pulse width and controls in3ector synchronization by turning the individual ground paths to the injectors On and Off.
The PCM adjusts ignition timing and engine idle speed. Engine idle speed is adjusted through the idle air control motor.
Cruise or Idle Mode
This is a CLOSED LOOP mode. The PCM recognizes an abrupt increase in throttle position or MAP pressure as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased fuel demand.
When the engine is at operating temperature this is a CLOSED LOOP mode. During cruising speed the following inputs are received by the PCM:
- Engine coolant temperature
- Manifold absolute pressure
- Engine speed (crankshaft position sensor)
- Throttle position
- Exhaust gas oxygen content
- A/C control positions
- Battery voltage
The PCM adjusts injector pulse width and controls injector synchronization by turning the individual ground paths to the injectors On and Off.
The PCM adjusts engine idle speed and ignition timing. The PCM adjusts the air/fuel ratio according to the oxygen content in the exhaust gas.
Acceleration Mode
This is a CLOSED LOOP mode. The PCM recognizes an abrupt increase in throttle position or MAP pressure as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased fuel demand.
Deceleration Mode
This is a CLOSED LOOP mode. During deceleration the following inputs are received by the PCM:
- Engine coolant temperature
- Manifold absolute pressure
- Engine speed
- Throttle position
- Exhaust gas oxygen content
- A/C control positions
- Battery voltage
The PCM may receive a closed throttle input from the Throttle Position Sensor (TPS) when it senses an abrupt decrease in manifold pressure. This indicates a hard deceleration. The PCM may reduce injector pulse width or the number of injectors firing per engine revolution. This helps maintain better control of the air/fuel mixture (as sensed through the O2S sensor).
Wide Open Throttle (WOT) mode
This is an OPEN LOOP mode. During WOT operation, the following inputs are received by the PCM:
- Engine coolant temperature
- Manifold absolute pressure
- Engine speed
- Throttle position
When the PCM senses WOT condition through the Throttle Position Sensor (TPS) it will:
De-energize the air conditioning relay. This disables the air conditioning system.
The exhaust gas oxygen content input is not accepted by the PCM during WOT operation. The PCM will adjust injector pulse width to supply a predetermined amount of additional fuel.
Ignition Switch Off Mode
When the ignition switch is turned to the OFF position, the following occurs:
- All outputs are turned off.
- No inputs are monitored.
- The PCM shuts down.
SYSTEM DIAGNOSIS
Operation
The PCM can test many of its own input and output circuits. If the PCM senses a fault in a major system, the PCM stores a Diagnostic Trouble Code (DTC) in memory.
For DTC information see On-Board Diagnostics.
CCD BUS
Various controllers and modules exchange information through a communications port called the CCD Bus. The PCM transmits the malfunction indicator (check engine) lamp On/Off signal, engine RPM and vehicle load information on the CCD Bus.