Modes of Operation
The PCM has several operating modes for fuel control, depending on the
information it receives from the sensors.
Starting Mode
When the key is first turned On, the PCM will turn on the fuel pump
relay for two seconds. The fuel pump runs and builds up pressure in the fuel
system. The PCM then monitors the MAF, IAT, ECT, TP sensors and ICM signal
to determine the required injector pulse width for starting.
Clear Flood Mode
If the engine is flooded with fuel during starting and will not start,
Clear Flood Mode can be manually selected. To select Clear Flood Mode, push
the accelerator to Wide Open Throttle (WOT). With this signal, the PCM will
completely turn Off the injectors and will maintain this as long as it sees
a WOT condition with engine speed below 1000 RPM.
Run Mode
The run mode has two conditions: Open Loop and Closed Loop. When the
engine is first started and engine speed is above 400 RPM, the system goes
into Open Loop operation. In Open Loop, the PCM ignores the signals from
the oxygen sensors and calculates the required injector pulse width based
primarily on inputs from the MAF, IAT and ECT sensors. The system will stay
in Open Loop until the following conditions are met:
| • | One oxygen sensor has varying voltage output, showing that it
is hot enough to operate properly. |
| • | The ECT sensor indicates above 80°C. |
| • | A calibrated time delay has elapsed after starting the engine.
This delay allows all sensors to stabilize. |
When these conditions are satisfied, the PCM goes into Closed Loop operation.
In Closed Loop, the PCM adjusts the calculated injector pulse width for each
bank of injectors based on the signals from each oxygen sensor.
Acceleration Mode
The PCM monitors changes in TP and MAF sensor signals to determine when
the vehicle is being accelerated. The PCM will then increase injector pulse
width to provide more fuel for improved driveability.
Deceleration Mode
The PCM monitors changes in TP and MAF sensor signals to determine when
the vehicle is being decelerated. The PCM will then decrease injector pulse
width or even shut Off injectors for short periods to reduce exhaust emissions.
Battery Voltage Correction Mode
When the PCM sees a low battery voltage condition, it can compensate
to maintain acceptable vehicle driveability. It does this by:
| • | Increasing the injector pulse width to maintain the proper amount
of fuel delivered. |
| • | Increasing the idle speed to increase generator output. |
Load Management Control Mode
When the HVAC controller has a request for rear window defog at idle,
the HVAC controller sends a message via Class II Serial Data to the PCM to
increase the desired idle speed. The changes to desired idle speed are as
follows. At idle in park/neutral desired idle speed will be at least 1040
RPM. When a gear other than park or neutral is selected, the desired idle
speed will be at least 704 RPM.
Fuel Shut-Off Mode
The PCM has the ability to completely turn all the injectors Off or
selectively turn Off some of the injectors when certain conditions are met.
These fuel shut-off modes allow the Northstar powertrain to protect itself
from damage and also improve its driveability.
The PCM will disable all eight injectors under the following conditions:
| • | Ignition Off (prevents engine run-on). |
| • | Ignition On but no ignition reference signal (prevents flooding
or backfiring). |
| • | High engine speed (above red line). |
| • | High vehicle speed (above rated tire speed). |
| • | Extended high speed closed throttle coastdown (reduces emissions
and increases engine braking). |
The PCM will selectively disable up to four injectors under the following
conditions:
| • | Torque Management enabled (transaxle shifts or abusive maneuvers). |
| • | Traction Control enabled (in conjunction with front brakes applying). |
| • | Low coolant condition (protects engine from overheating). |
