Yellowstreak
New member
Just an FYI in case any fellow boaters have had a problem with their Merc 4.3 MPI going into Guardian Mode and no retrievable or reliable codes coming up. I had a problem that got progressively worse. Eventually boat would not even plane out. Surged at 2800-3000 RPM. Suspect water pressure sensor was replaced. Not the solution. Turns out Merc placed the sensor too close to ignition coils and was getting EMI that fooled the ECM into thinking Guardian was appropriate. A relocation kit was supplied, ECM reflashed, problem solved. Maybe I can save someone else some valuable time and money making unnecessary trips to the lake and the dealer.