I have been trying to fix this engine for over a year now with no success. I’ve tried to find a professional mechanic to fix it and the only two I could get to come look at it both just said they don’t know what’s wrong with it and good luck. It’s a 1996 Mercruiser 7.4LX MPI (Gen V) with a Bravo 3 stern drive mounted in a 270 Sundancer.
So far I’ve replaced the cylinder heads, exhaust manifolds, the spark plugs, spark plug wires, cap, rotor, distributor, ignition coil, ignition module, air temp sensor, MAP sensor, IAC, throttle position sensor, mechanical fuel pump, the electric pump in the vapor separator tank, the alternator, raw water impeller and housing, the heat exchangers, thermostat and housing, engine temp sender, oil pressure sender, the entire outdrive, and repaired or replaced wiring. I have quadruple checked the timing and fuel pressure. All is set exactly as it should. Fuel in the tank has been flushed and replaced with new. Oil is fresh and pressure is good. Engine coolant temperature is fine. Compression in all 8 cylinders is 120 psi and testing for spark at all 8 cylinders showed no problems.
But still it has a hard time starting when cold and it will not throttle past 2000 rpm’s under load. Fuel pressure remains at 37 at the rail when under load and adjusting the timing either more retarded or advanced makes no difference. If I had to guess I’d say it almost feels like it’s running to lean but the plugs look normal.
I am at a complete loss as to what’s wrong with this motor. Has anyone ever run into something like this? If so what was the issue and how did you fix it?
So far I’ve replaced the cylinder heads, exhaust manifolds, the spark plugs, spark plug wires, cap, rotor, distributor, ignition coil, ignition module, air temp sensor, MAP sensor, IAC, throttle position sensor, mechanical fuel pump, the electric pump in the vapor separator tank, the alternator, raw water impeller and housing, the heat exchangers, thermostat and housing, engine temp sender, oil pressure sender, the entire outdrive, and repaired or replaced wiring. I have quadruple checked the timing and fuel pressure. All is set exactly as it should. Fuel in the tank has been flushed and replaced with new. Oil is fresh and pressure is good. Engine coolant temperature is fine. Compression in all 8 cylinders is 120 psi and testing for spark at all 8 cylinders showed no problems.
But still it has a hard time starting when cold and it will not throttle past 2000 rpm’s under load. Fuel pressure remains at 37 at the rail when under load and adjusting the timing either more retarded or advanced makes no difference. If I had to guess I’d say it almost feels like it’s running to lean but the plugs look normal.
I am at a complete loss as to what’s wrong with this motor. Has anyone ever run into something like this? If so what was the issue and how did you fix it?
