Boat Repair Questions? Ask a Marine Mechanic for Answers ASAP
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I doubt this is your ECM.
First, make sure you are getting good gas. You must use the premium grade in Mexico.
The surging indicates that you have a vacuum leak in the motor, or air in the fuel lines.
Check that all of the fuel lines are tight on the vacuum side of the fuel pump. Notice any cracks in the rubber or any pinched hoses.
Replace the water separating fuel filter, water in that can cause fuel starvation as well.
You need to check your fuel pressure when the problem is occurring. That will require a fuel pressure gauge attached to the fuel rail and running the boat, in the water, until the problem occurs and you can get a reading. You are probably going to find it is dropping off. If this is the case, replace the fuel pump.
Check your for loose ignition coil ground wires, and the coil(s) for cracks or signs of carbon tracking.
Otherwise, you are going to need to have the ECM read for fault codes. You may have a faulty knock sensor, cam or crankshaft position sensor, or throttle position sensor.