Automotive Vehicle Strategies and ECM Modes (Diagnostic Strategies of Modern Automotive Systems Book 5) by Mandy Concepcion

Author:Mandy Concepcion [Concepcion, Mandy]
Language: eng
Format: mobi
Tags: auto-training, electronics, automotive technician, obd ii, automotive, obd2, computer networks, auto-technology, mechanic, auto, technician, auto-repair, obdii, auto-electric
Publisher: www.autodiagnosticsandpublishing.com
Published: 2011-05-29T16:00:00+00:00

The seven main fuel control modes are – cranking enrichment, engine warm-up, open-loop, closed-loop, acceleration enrichment, deceleration enleanment and idle speed control.

Several other modes of operation exist and apply to specific systems or conditions.

These are – clear flood, limp-in-mode, variable valve timing, selective fuel injector cut-off and synchronous and asynchronous fuel injection.

These modes are explained in the following pages.

Section: Cranking Enrichment MODE

* Cranking enrichment mode – The ECM provides the extra fuel needed to start the engine. This is done by increasing the injector pulse width to as much as 40 mS and using injector group firing, as opposed to sequential. This mode is activated whenever the ignition key is switched on. As soon as the engine starts and its speed goes above a certain RPM value, the ECM switches to the next logical mode, whatever that may be.

On certain vehicles, a start/crank input from the starter relay or solenoid is provided to the ECM. This signal may reach the ECM through either a fuse or a direct wire connection. A failure in this circuit may cause severe performance problems, such as excessive fuel delivery – if this signal is shorted to power. Or it may also cause long cranking time – if this signal does not reach the ECM (the ECM does not know it has to go into cranking mode).

During cranking mode, the ECM constantly compares the ECT sensor value with a look-up table stored in ROM memory to determine the correct injector pulse-width. Normal cranking mode A/F ratio is between 1.5:1 to 12.0:1 depending on engine coolant temperature. The main reason for this mode is that at colder temperatures the fuel tends to form into large droplets, which do not burn as efficiently. For this reason, manufacturers are constantly looking for ways to reduce the cranking and warm-up mode times as much as possible, since they are the greatest cause of automotive air pollution in modern engines.

As a side note, the low voltage sub-mode also plays a role while at cranking enrichment mode. The low voltage submode program code instructs the ECM to further increase injector pulse to compensate for the lower fuel pressure, brought about by the lower available fuel pump voltage from the starter motor cranking the engine.

Regardless of whatever mode is active, a low supply voltage will increase injector pulse.

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