Engine Controls - Theory & Operation - 5.2L: Overview Dodge Dakota WS

Modes Of Operation

As input signals to PCM change, PCM adjusts its response to output devices. Modes of operation come in 2 types, open loop and closed loop. In open loop mode, PCM is not using input from oxygen sensor and is responding to preset programming to determine injector pulse width and ignition timing. In closed loop mode, PCM is adjusting ignition timing and using input from oxygen sensor to fine tune injector pulse width.

The following inputs are used to determine PCM mode

1. A/C Control Positions
2. A/C Switch
3. Battery Voltage
4. Brake Switch
5. Camshaft Position Sensor
6. Coolant Temperature Sensor (CTS)
7. Crankshaft Position Sensor
8. Engine Speed
9. Park/Neutral Position Switch
10. Idle Contact Switch
11. Manifold Absolute Pressure (MAP) Sensor
12. Oxygen Sensor (O2S)
13. Starter Relay
14. Throttle Position Sensor (TPS)

From these inputs, PCM determines which mode vehicle is in and responds appropriately. Not all inputs are used in all modes or by all models. Modes of operation are

1. Ignition Switch In ON Position (Zero RPM)

This is an open loop mode. PCM determines atmospheric pressure from MAP sensor and determines basic fuel strategy. PCM modifies fuel strategy according to TPS and CTS. ASD relay is not energized.

1. Engine Start-Up

This is an open loop mode. When starter is engaged, PCM receives distributor signal and energizes Auto Shutdown (ASD) relay. See AUTO SHUTDOWN (ASD) RELAY under MISCELLANEOUS CONTROLS. Once ASD relay is energized, PCM determines proper injector pulse width and ignition timing from input signals. During engine start-up, PCM energizes all injector(s) simultaneously until it determines crankshaft position.

1. Engine Warm-Up

This is an open loop mode. PCM determines injector pulse width using information from various inputs and controls each injector sequence and pulse width. PCM controls engine idle speed, throttle stop angle and ignition timing.

1. Cruise Or Idle

When engine is at operating temperature, system will leave open loop mode and move into a closed loop mode. Using information from various inputs, PCM determines injector pulse width. PCM controls engine idle speed (using IAC motor), throttle stop angle and ignition timing. PCM determines proper air/fuel ratio (14.7:1) using input from oxygen sensor(s).

1. Acceleration

All models are in open loop mode. When PCM recognizes an abrupt increase in throttle position or MAP pressure as a demand for increased engine output, it increases injector pulse width in response to increased fuel demand.

1. Deceleration

When engine is at operating temperature, this is an open loop mode. On hard deceleration, with proper RPM and closed throttle conditions, PCM will ignore O2S input and enter a fuel cut-off strategy. If a hard deceleration does not exist, PCM will maintain proper injector pulse width and continue injection. PCM disengages A/C compressor clutch until vehicle is no longer under deceleration.

1. Wide Open Throttle (WOT)

This is an open loop mode. When PCM senses wide open throttle, it grounds EGR and EVAP purge solenoids to prevent EGR and EVAP purge functions. Oxygen sensor input is not utilized and PCM adjusts injector pulse width to supply a predetermined amount of additional fuel.

1. Ignition Switch In OFF Position

This is an open loop mode. All fuel injection is stopped. PCM de-energizes Auto Shutdown (ASD) relay and extends Idle Speed Control (ISC) actuator (if equipped) in anticipation of next start-up.