Mercruiser 5.0 MPI Constant Alarm when speed up and power reduced

[s199810]

when reduce power to idle, alarm gone. When press the throttle-only button (disengage the gear) and rev up, no alarm at all. Drive unit oil full. What could be the problem? drive unit related? As from the service manual, the engine guardian stratety monitors, 1. oil pressure, 2. coolant temp., 3seawater pressure, 4, engine overspeed, 5. exhaust manifold temp., so if the engine guardian alarm sets off, it should be same no matter if the gear is engaged or disconnect from the engine, right? why it does not setoff when I disengage the gear and rev up the engine?

 

[achris]

Year and serial number?

when reduce power to idle, alarm gone. When press the throttle-only button (disengage the gear) and rev up, no alarm at all. Drive unit oil full. What could be the problem? drive unit related?

There's 2 ways to find this. The expensive way, just keep replacing parts until you find it. And if it's a sensor that's reading the right information, that won't fix it, and you'll have a lot of spares, and still an engine with a fault... Or hook up the diagnostic software, read the codes and find out WHICH sensor is indicating a problem, then fix the problem.

As from the service manual, the engine guardian strategy monitors, 1. oil pressure, 2. coolant temp., 3seawater pressure, 4, engine over-speed, 5. exhaust manifold temp., so if the engine guardian alarm sets off, it should be same no matter if the gear is engaged or disconnect from the engine, right?

Wrong. One of the sensors on an MPI engine is an 'in gear' switch. The ECU knows when the drive is in gear, and when it's not.

why it does not setoff when I disengage the gear and rev up the engine?

Because it knows the drive isn't in gear, and there isn't any load on the engine.

Chris.....

 

[s199810]

Wrong. One of the sensors on an MPI engine is an 'in gear' switch. The ECU knows when the drive is in gear, and when it's not.
Because it knows the drive isn't in gear, and there isn't any load on the engine.

Chris.....

Thanks, that makes a lot of sense.