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Black Box Mystique: What is an EMM and how does it work?

by ‎10-19-2011 02:20 - edited ‎10-19-2011 02:41


Whether you call it a "brain box" or a "black box", the engine management module (EMM) is  the control center that directs everything required to make your E-TEC operate correctly. Gone are the days when you adjusted idle rpm, fiddled with the carburetor mixture needles, and went through a complex procedure of synchronizing the throttle with the timing linkage to make an outboard motor run well. Today the computer on your outboard is the equivalent of a commander in chief.




The EMM was introduced with the model year 2000 Evinrude outboards. Prior to that, and with other manufacturers, engine computers were called Electronic Control Units or ECUs. The major difference is that the EMM not only monitors the engine operation, but it also rectifies and regulates the AC  alternator voltage and oversees the electrical systems. All this is contained in one compact unit, unlike an ECU which requires additional external components and wiring to accomplish the same things.


An EMM by itself, as the old saying goes, is dumber than a box of rocks. It is only a combination of special electronic parts that can't do anything unless they are "taught" specifically what to do. Erroneously called software, the operating instructions for each particular outboard are electronically "burned" into the EMM main logic chip, which is just like the BIOS chip on your personal computer. The programming is also called a MAP or a look-up table. The Evinrude EMM programming can be updated by a dealer as conditions warrant unlike other company's control modules that have to be replaced. 


To keep your Evinrude compliant with EPA emission regulations, the EMM has safeguards built in so they cannot be used on other motors or to affect power output and emissions.  The EPA has strict penalties for tampering with emission control parts or trying to change horsepower. The engine serial number and operating history is a permanent part of each individual EMM. Every fuel injector has a unique identification number describing its flow characteristics and that along with its cylinder location is programmed into memory. This is why EMMs and injectors cannot be interchanged among different outboards.


Engine temperature, RPM, throttle opening, charging voltage, and barometric pressure are just a few of items that are monitored by the engine management module. From that information, the EMM controls the output and the timing of the fuel system and the ignition system to make each cylinder deliver optimum power at that particular moment. It is equivalent to getting a tune up every time a cylinder fires. At 5800 rpm this happens around 576 times per second on a 6 cylinder outboard. The EMM probably makes over a million calculations per minute if you count all the data and all the output commands required for full throttle.


The EMM cannot think, it only gathers information, compares it to the MAP or look-up chart, then sends commands to the fuel injectors and to the ignition system. In addition it manages the charging system and the oiling system for the motor and generates warning alarms, tachometer pulses, and I-Command data for most models. There are 4 built-in LEDs that can be used for engine diagnostics. Read the EMM sticker for troubleshooting with the illuminated LEDs.


You can think of the EMM as an executive decision maker sitting at a desk. His various employees, the input sensors, run into the office and start yelling:

"Hey boss, the motor is running 4000 rpm"

"Hey boss, the engine temperature is 160°"

"Hey boss, the throttle is at 75%"

"Hey boss, the air temp is 82°"

"Hey boss, the battery is at 14 volts"

"Hey boss, the barometric pressure is 29.92"

The decision maker then considers all of the inputs and looks up the information on his reference chart ( MAP ) that says if the throttle is 3/4 and the rpm is 4000, then the spark timing should be this setting and the fuel delivery should be this amount. The other factors including temperatures, exhaust backpressure, and barometric pressures slightly modify (trim) the spark and fuel commands according to another lookup chart. After studying the data, the decision maker yells commands to his other underlings, the output actuators.

"Set the #1 spark timing to 28° before top dead center"

"Set the #1 fuel injector to deliver X amount of gasoline 1 microsecond before the sparkplug fires"

"Increase the battery voltage to 14.5 "

"Pulse the oil injector 2 times"

All this occurs about 576 times per second at full speed.



The image below illustrates the various sensors and actuators on a typical V-6 Evinrude E-TEC.



1. Engine Management Module (EMM)

2.Battery(12 volt)

3. Key switch (switched B+, start signal)

4. Stator

5. Knock sensor

6. Crankshaft Position Sensor (CPS)

7. Throttle Position Sensor (TPS)

8.  Shift Interrupt Switch

9. Air Temperature Sensor (AT)

10. Oil Pressure Sensor (component of 18)

11. Engine Temperature Sensor(s)

12. Water in Fuel Sensor / Fuel Filter

13. Trim / Tilt Sending Unit

14. Water Pressure Sensor w/adaptor harness

15. LED indicators

16. Fuel Pump (high pressure)

17. Starter Solenoid

18. Oil Injection Pump and Manifold

19. Rear Oil Injector and Manifold

20. Ignition Coil

21. Fuel Injector

22. Tachometer/SystemCheck Gauge

23. I-Command (CANbus) Display

24. Diagnostic Connector

25. Trim and Tilt Relay Module

26. Oil Level Switch




The EMMs use different internal components and modules according to the engine sizes. From 15hp to 30hp, the EMM is a small clear plastic module. The 40hp through 90hp motors use a larger EMM housing while the V-4 and V-6 versions contain a greater number of components and circuits.




Although some people may not embrace the idea of having a computer controlling the engine, it is the Evinrude EMM that makes the E-TEC such an emission-friendly, smooth-running, and efficient outboard motor.

‎10-20-2011 06:16 - edited ‎10-20-2011 06:21

Heres you can see that the EMM is watercooled.


on ‎11-07-2011 07:22



Here is a cut-a-way image of a V-6  EMM