I've bought a boat with a bad engine. I plan to replace the long block with a 300 HP version of the same engine. Will the ECM handle it or do I need to just stay with 260 HP.
It's a 1998 year model.
Did they make a 300hp version in the same year as your engine? If so, perhaps your ECU could be reflashed with the tune for the 300hp version. If not, I would not run the 300hp engine run with the tune from a 260hp engine. 300hp takes more fuel to run properly than 260hp, and with no O2 feedback in the stock ECU system (like a car/truck has), it wouldn't know if the engine weren't running properly.
Another option would be to add a piggy back device called the Dynojet CMD Marine unit to it. It's a plug-and-play fuel controller that connects between the stock fuel injector connectors and the fuel injectors. It reads the injector pulse sent out by the ECU, then lets you adjust the fuel delivery using a simple fuel map. The map is set up as RPM vs. manifold pressure.
To make things even easier, you can add our wideband O2 sensor kit to the engine to monitor air/fuel ratio in real time. You can even enable an option in the CMD Marine unit called AutoTune, which lets you set a target air/fuel ratio for each cell in the fuel table. When the engine is running in that cell, the CMD Marine will compare the actual air/fuel ratio to the target air/fuel ratio and create a trim to adjust the fuel delivery to achieve your desired target and build your fuel table while you run the engine.
Not sure what engines were available then. I still haven't completely decided what to do. It's 'only' in a pontoon so I don't need tremendous hp. I was just thinking if I could just swap it out, I might go for the higher hp long block. Thanks for the info.