After reading a lot of the postings in this forum I notice that a lot of people have near the same issue as i'm having with my merc 5.7L LX quiting at about 4000RPMS instead of making it near 5000RPMS. I've now tried everything from changing the wire harness for the ICM, replaced coil, checked tach with shop tach to confirm, took every voltage reading I could and confirmed with the merc specs, checked rotor and cap, replaced my bad battery. So now im down to either a bad ICM (which from my drag racing days seems like a pain in the *** with the way the thunderbolt V system is setup im thinking if i do change the module im going to just ditch the knock sensor setup and go with the marine MSD ignition conversion). I doubt it the carb since the motor runs great from idle to 4000Rpms and pushes the boat to 50 MPH with no problem. Maybe a fuel delivery issue??? Or even low voltage on the alternator but I checked it at the coil at idle of 600rpms and had 12.7 Volts. These engines are fairly basic and easy to work on if your used to working on Chevy 350's that we used in our drag cars. Just a costly next choice to change the ICM when it may be something else and then im stuck with a $400 ICM that I cant return.
