Understanding the EFI Process


What an EMS Sees for Inputs and Generates for Outputs

An engine management system is simply a computer which understands inputs generated from specialized sensors which have been designed to work in the harsh environment of a running engine. Most vehicles engine management systems are designed to work with 12 volt and 5 volt DC circuit systems.

Below are the common triggers or inputs seen by the EMS. These signals are used to help time the engine and to let the EMS know where the engine is as far as the crankshaft and camshaft rotation is concerned. This information is also used to tell the EMS the position of the pistons and valves in relation to TDC for each cylinder.

ECU Sensor Waveforms

Now we will go over the detailed processes that the EMS completes in order to control various aspects of an engine’s electronics.

1) Input triggers and input signals coming in to the EMS. This information can come via analog or digital signals (RS232 or CAN).

2) EMS “looking-up” what to do according to the table calibration (Ex. Fuel, Ignition, Boost, Camshaft Phasing, etc.)

3) EMS applying compensatory corrections to output based on engine sensors.

4) EMS applying learned adjustments from its Short-Term and Long-Term memory

5) EMS finishes calculations and sends signals to output devices (fuel injectors, coils, solenoids, driver motors, etc.).

Square wave

The above square wave is a standard output of most EMS drivers. These square wave signals are used to control fuel injectors, boost control solenoids, camshaft phasing mechanisms, emission solenoids, electric throttle body motors, etc. Modern Engine Management Systems have the accuracy and speed necessary to precisely control various output devices.

Understanding The Mechanics and Plumbing of Four Different Modern Fuel Systems

1) Low pressure (3-8 psi) carburation return fuel system

Low Pressure

2) High pressure EFI return fuel system

high pressure efi return fuel system

3) High pressure EFI returnless fuel system

high pressure EFI returnless fuel system

4) Ultra High Pressure EFI return & returnless for DISI and CID

Ultra high pressure EFI return and returnless fuel system

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