The Signs & Symptoms of a Faulty Electronic Control Module in a MerCruiser

ECM Reset

• A MerCruiser ECM will reset when there is a voltage drains suddenly. Primarily found on boats with dual MerCruiser engines, this problem causes the ECM to shut down and the engine will not start. Sometimes the ECM will reset without a problem and the engine will only sound like an ignition miss. If the voltage does not return to the minimum amount required by the ECM, the engine will not start until the voltage requirement is repaired.

Blown ECM

• One of the major problems with the ECM is when the computer blows. The engine will begin to miss out or not accelerate to the desired speed. The main cause of an ECM blowing is attaching accessories into the engine's electrical harness. Splicing wires into the engine's wiring harness to run other devices will also cause the ECM to fail.

Not Starting

• The MerCruiser ECM controls the ignition system on the engine. If the engine will not crank, there could be a problem with the ECM. Once the ignition switch is engaged, the ECM tells the electrical wiring harness to power up. Voltage is sent from the battery to the alternator and into the starter, which provides the initial current for the spark plug or plugs, firing the engine. A failing ECM will prevent this signal from being sent and the engine will not start.

Missing Out

• Another symptom that the ECM is failing is when the engine begins to miss under normal operating conditions. The ECM controls the amount of fuel distributed through the fuel injectors. When the ECM is failing, the fuel injector system is not being instructed how much fuel to spray into the cylinders. If the cylinders do not get enough fuel, then the engine will begin to miss and cough.