EMM Unwrapped

What is an EMM and how does it work?


Whether you call it, a “brain box” or a “black box”, the engine management module (EMM) is the Grand Central Station of your outboard motor. It controls everything to make your E-TEC operate correctly. Gone are the days when you adjusted idle rpm, fiddled with the carburetor mixture needles, and worked through a complex procedure of synchronizing the throttle linkage to make a motor run well. Today the computer on your outboard is the equivalent of an onboard engineer.



The EMM was introduced with the model year 2000 Evinrude outboards. In prior years, along with other manufacturers, onboard computers were called Electronic Control Units or ECUs. The major difference is that an EMM not only monitors the engine operations, but it also regulates the AC alternator voltage, charges the batteries, and oversees the electrical systems. All this is contained in one compact unit, unlike an ECU which requires multiple external components and additional 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 collection of electronic parts that can’t do anything unless they are “taught” specifically what to do. Erroneously called software, the operating instructions (firmware) for each particular outboard are electronically “burned” into the EMM main logic chip, similar to the BIOS chip on your personal computer. The instruction set is also called a MAP or a look-up table. The Evinrude EMM programming is easily updated by a dealer with a laptop as conditions warrant or when improvements are available. Other outboard companies normally have ECUs which cannot be upgraded or improved without replacing them with another unit.


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 controls or trying to change horsepower output. The engine serial number and operating history are 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 the EMM memory. This is the reason why EMMs and injectors cannot be interchanged between 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. According to Evinrude engineer George Broughton, the EMM handles about eight million calculations per minute if you count all of the data and the commands required for full throttle operation.


The EMM cannot think, it only gathers information, compares it to a look-up table, then sends specific commands to the fuel injectors and to the ignition system. In addition it manages the battery charging and the engine’s oiling system. It also generates warning alarms, a tachometer signal, and the NMEA2000 networking data. A unique feature of the EMM is the four built-in LEDs which can be used for engine diagnostics. A yellow sticker on the cover informs the operator how to troubleshoot the engine using the illumination sequence of the LEDs. 


To understand how an EMM operates imagine an executive sitting behind a desk. His various employees, the input sensors, run into the office and start telling him:

“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 executive considers all of the input data and refers to the look-up table (MAP) that says if the throttle is 3/4 and the rpm is 4000, then the spark timing should be at this setting and fuel delivery should be this amount. The other factors such as air and engine temperatures, exhaust backpressure, and barometric pressure slightly modify (or trim) the spark and fuel commands according to a different lookup chart. 


After reviewing the information, 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 volts”

“Pulse the oil injector 2 times”

On a V-6 outboard all of these input and output calculations occur at over 133,000 times per second at full throttle.


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




1. Engine Management Module (EMM)

EMM42. 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

EMM316. 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 have different internal components and modules depending on the engine model family.  From 15hp to 30hp, the EMM sits inside a clear plastic case. The 40hp through 90hp outboards require a larger EMM module while the V-4 and V-6 versions use the same housing but a greater number of components and circuits for the additional cylinders and the NMEA2000 networking data.


Although some people may not embrace the idea of having a computer controlling all aspects of engine operation, it is the EMM that allows the motor to run efficiently, protects the outboard if something goes wrong, and keeps emissions within EPA regulations. As with cell phones, home entertainment, and vehicles, today’s electronics allow us conveniences that were unheard of only a generation ago.