Everything You Need To Know About Boat Computer Plugins

Whilst there are a few different names for plugging into a boat computer, for this article we’re going to call it the Engine Control Module (ECM). We will explain the reasons why you would plugin to the computer, and what you can expect to achieve from doing so. Typically engines can have multiple “computers” fitted, but there is only one that is used for diagnostics and read outs.

MerCruiser ECM

They can also be referred to as:

Engine Control Unit (ECU)
Diagnostic Port
Engine Computer
Engine Control Module

What are ECM diagnostics?

Modern marine engines are electronically controlled, and have that little black box where the “magic happens”. That little black box is the ECM or ECU (engine control module/unit) – consider it the engine’s brain. The ECM receives “inputs”, analyses the data and delivers “outputs”. An example of an “input” could be crankshaft and camshaft position (so the engine knows where each piston is at any given time). With this input the ECM now knows when to “output” the signal for fuel injection and spark to the given cylinder. 

The list of possible engine inputs can become exhaustive, some further basic examples are oil pressure, coolant temperature, throttle position, inlet manifold pressure and exhaust manifold temperature. If any of the engine’s ECM inputs go outside of the preset parameters the engine can sound a warning alarm and potentially de-rate / limit the RPM of the engine to prevent significant damage to the engine occurring.

Marine engine manufacturers each have their own engine management software and diagnostic tool. A diagnostic tool is a computer program that has the ability to exchange information with the engine’s ECM. 

At BoatBuy, we have the ability to complete a ECM plugin on most petrol engines, inboard and outboards should you request it. 

What is an ECM plugin?

An ECM plugin is where a diagnostic tool is connected to the engine’s computer to read current and historically saved data. 

Do all engines have an ECM and how do I know if I can plug-in to the ECM?

No, not all engines have an ECM. Generally if your engine is equipped with EFI (electronic fuel injection) there is the ability to connect to the ECM to read data. Even some carbureted engines can be connected to with limited data, such as engine hours available. Pre-1992 there is no ability to complete an engine diagnostic reading.

What does the ECM plugin tell me?

Pending the manufacturer, data that may be available can include:

  • Total engine hours
  • Engine runtime in given RPM ranges
  • Active faults
  • Logged faults
  • Occurrences of faults with a snapshot of all engine data at the time of fault
  • Sensor failures
  • Engine start count
  • The amount of times the engine has shifted gears

Is an ECM plugin worth it?

An ECM plugin can be beneficial as it gives us the opportunity to review a history that has been saved by the engine. Without it, it’s simply guesswork to the life the engine has endured. If an alarm has sounded it should log an event in the engine’s memory. By opting for an ECM plugin we can get a glimpse into the history of the engine. This can be beneficial for checking whether there has been any historical or reoccurring overheats or low oil pressure events, which can result in significant internal engine wear and potential damage. The only downside is with some engine manufacturers the fault history can be cleared, which can make it impossible to see if any faults have occurred.

The boat doesn’t have an hour meter, is this an issue?

A boat without an hour meter or with an hour meter that doesn’t work, is like a car that has had its odometer disconnected. You might think you are getting the deal of a lifetime on an early model low hours boat, only to find out the petrol engine has turned out over 2000 hours and is well overdue for rebuild or a re-power. With that being said, there are usually other tell-tale signs to high hours such as blow by, steering play, or low compression for example.

Should I get the ECM plugin?

This option is completely up to you, the ECM plugin has its pros and cons. 

The single ‘con’ that comes to mind, is that the only data available to be read on some engines is total engine hours and hours logged per RPM range, with no history of engine faults or events. This actually sounds more like a ‘pro’ as there has been less historically noted faults or events for the ECM to record. 

How can an ECM plugin be used for diagnostic troubleshooting?

Multiple tests can also be performed with a diagnostic tool. These can include (but not limited to depending on the manufacturer):

  • IAC function
  • Fuel pump relay function
  • Injector cut out test
  • Relative compression

Here is a basic example of how the diagnostic tool can be of assistance when attempting to diagnose a fault:

If your engine does not achieve its rated RPM, your engine could be missing on a cylinder. First you could perform a cylinder drop test (removing a spark plug lead with the engine running and listening for a drop in engine RPM, to confirm spark to the cylinder). To complement the drop test you could use the diagnostic tool to complete an injector cut out test. At the click of a button you can prevent the injector from delivering fuel to the given cylinder (again listening for a drop in the engine’s RPM). Pending the engine you may be able to complete these by hand, but when access is limited, further removal of parts will be required to complete successfully. Both of these tests could be completed per cylinder with the diagnostic tool, saving time and also being the safer alternative.

Screenshots of invaluable data on various manufacturers ECM printouts

Curious about what the printouts actually show? Here’s a few screenshots from some popular ones.

Volvo ECM Readout
Volvo ECM Printout Showing High Exhaust Gas Temperature
Suzuki ECM Printout
Suzuki ECM Printout With 1/3 Running Hours At Idle
Evinrude eTec ECM Printout
Evinrude ETEC Showing Critical Overheat
MerCruiser ECM Readout
MerCruiser ECM Readout Showing Guardian Mode At 424 Hours
About the Author – Brendan Sutton

Brendan is a dual-certified Marine Surveyor & Engineer, who completed his trade at well respected marine engineering company based on the Hawkesbury River. After relocating his family to the Gold Coast, he joined the BoatBuy team in QLD. Liked this article? We would love to hear from you. Feel free to email Brendan with any boating related questions you might have here.


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