Starting the Engine / Ignition Key

Overview

Starting the engine may be controlled by the ECU, in response to configurable input signals.

To start the engine, the fuel pump must be powered, the engine is primed with fuel, the starter motor must turn the engine over, timing wheel(s) synchronization must be established, and ignition and injection events must then occur with sufficiently precise timing to ensure that the engine starts powering itself.

Cold engines require a richer fuel mixture due to reduced fuel vaporization and increased oil viscosity. The ECU provides methods of enriching the fuel mixture during cranking and warm-up.

When stopping the engine, the ignition key is turned off, and the ECU will stop fuel injection, park the idle stepper motor, and turn off power to the fuel pump and the ECU itself (Main Relay control).

Starter Control

option iconStarter In is a configurable switch input to request the starter motor to run. This is typically connected to the ignition key in the ‘crank’ position. If starting of the engine is managed externally, then option iconStarter In may be left un-configured.

option iconStarter Out is a configurable output that will be energized when the starter motor should be turned on. This is typically connected to a relay coil that switches the high current supply to the starter motor.

option iconStarter Time out configures the maximum time that the starter motor will be energized. This is a safety feature to prevent damage to the starter motor if the engine fails to start.

option iconStarter Exit Speed configures the engine speed at which the starter motor will be turned off, assuming that the engine has started turning itself over. Starter motors turn the engine over at a relatively low speed (typically up to 500 RPM) - the motor should be turned off as soon as the engine is running under its own power to avoid damage to the starter motor and unnecessarily draining the battery.

Cranking Detection

The cranking state is indicated by the channel iconStat Cranking channel. The ECU will report that it is in the ‘Cranking’ state as soon as it is turned on, even though the engine may not actually be turning.

The ECU indicates that the engine is actually in motion if channel iconStat Running is ON. The ECU will trigger any ignition or injection events until channel iconStat Sync'd is ON, indicating that the ECU has synchronized with the engine timing wheel(s). Synchronization is required to ensure that ignition and injection events occur at the correct time in the engine cycle.

When starting an engine, the ECU must compute an channel iconEngine Speed value prior to fully synchronizing with the crankshaft / camshaft timing wheel(s). The ECU estimates the engine speed using fewer crank teeth than a full engine cycle when channel iconStat Sync'd is OFF, see and Engine Speed (RPM) Calculation for details. This initial speed calculation uses option iconStart Actual Teeth, option iconStart Actual Teeth <2, option iconSpeed mul and option iconSpeed Cycle/rev.

option iconStart Crank Teeth configures the number of ‘synchronized’ teeth (channel iconT1 Count Sync’d) that must be detected before the ECU will exit cranking mode.

The channel iconT1 Count Sync'd channel is the number of actual crank teeth seen since engine synchronization was achieved and counts up until it reaches 255, at which point it stops counting. This channel can be useful to monitor short-term loss of synchronization; it is reset to zero if synchronization is lost.

option iconStart min Speed configures the minimum engine speed that must be exceeded before the ECU will allow ignition events to occur. Ignition events will need to start while the engine is being turned over by the starter motor, so this value should be set to a value that is achievable by the starter motor.

option iconCrank Exit configures the engine speed at which the ECU will exit the cranking state. This should be set to a value lower than the minimum idle speed of the engine, but higher than the speed that can be achieved by the starter motor. It indicates that the engine is running under its own power.

Ignition timing may be adjusted during cranking using the option iconStart Ignition option.

Synchronization During Cranking

Due to compression within the engine, the starter motor is unlikely to be capable of turning the engine smoothly, so wider missing / extra tooth tolerances may be required to account for the more significant variations in engine speed during cranking.

Option option iconStart MX Time is used in place of option iconMX Time when starting to determine the tolerance between crank teeth. Its value will depend upon the type of crank wheel (e.g. Missing or eXtra tooth) / sync strategy.

For configurations that normally use sequential ignition, cam synchronization may be ignored during cranking by setting option iconStart No Cam Sync to ON, effectively running the engine in wasted spark mode during cranking.

Start Pulse (Priming)

Warning

Engines using plastic inlet manifolds should not use this feature as the potential for backfire may severely damage / blast off the manifold.

The Start Pulse feature is not commonly required on modern engines; configuring the ECU to provide extra fuel during cranking is usually sufficient and safer.

To use the Start Pulse feature, the cranking position of the ignition key should be wired to the ECU, with the corresponding input pin selected in the option iconStart Pulse pin option. Note: option iconStart Pulse pin can be configured as an active low by making the option negative.

When the start pulse pin is asserted (and channel iconStat Cranking is ON), the ECU will fire all fuel injectors simultaneously with a channel iconStart Pulse duration of fuel.

channel iconStart Pulse is taken from the table iconStart Pulse table, which is indexed by the channel iconCoolant temperature channel.

The starter will turn the engine, and the ECU will try to synchronize with crank and cam timing signals.

The channel iconEngine Speed channel will be calculated after some timing wheel events have occurred, see Engine Speed (RPM) Calculation for details.

When the engine is synchronized, indicated by channel iconStat Sync'd = On, the ignition and fuel injection events will be allowed.

Note

if option iconStart Pulse pin was not detected the first cycle of injections will be extended by channel iconStart Pulse duration. channel iconAfter Start rev counter will increment until option iconCrank Exit speed is exceeded and normal running established, where upon the channel iconAfter Start timer will start.

Stopping

The ignition key is turned to Off, the channel iconMain Relay Off timer starts.

The following options specify time durations for shutdown tasks that are performed in sequence:

  • option iconMain Relay Stop Eng - fuel injection stopped, may take several seconds for the engine to run down.
  • option iconMain Relay Park IAC - resets and parks idle stepper motor.
  • option iconMain Relay Kill Pwr - turns off outputs - option iconOut Main Relay, and - option iconOut Main Relay 2.

This time must be long enough for idle motor to complete parking.

option iconMain Relay Safety will delay the turn off if there is non-volatile write of calibration data indicated by channel iconError EE Checksum if option option iconAuto EE is On.

Re-starting

If the ignition key is returned to on position, after channel iconMain Relay Off exceeds option iconStart Pulse Rearm Time, and option iconStart Pulse Rearm and option iconMain Relay Off Restart are On, the fuel pump will run again for option iconFuel Pump Prime seconds, and channel iconStart Pulse Pending will go On.