Merc 250

[03 202]

250 Pro XS. 1B826208. Coming out of whole alarm and limiter kick in at @2500 rpms. Also smart
craft says starboard motor over speed. If you back off throttle alarm stops. If I can ever get it to roll over and get on plane alarm stops after it gets @ 2800 rpms. Never seen this happen before. Any ideas? Going to hook it to computer Monday. Also while running any rpm after I get up there’s a random misfire.

[03 202]

Please move to Mercury 3.0 liter board.

[Savage]

Check the shift position switch.

[03 202]

Does the shift switch give problems. It feels good pressing on it. I will ck it with computer Monday

[tomloans]

This is probably an electrical issue. Battery or poor connections at battery terminal, alternator or poor connections, corrosion or loose cables at other critical connections. I am having the same issue and have gone through it pretty well and buttoned down and cleaned many connections. I bought a real good battery loader at Harbor Tools and my battery is in great condition. You might want to have your battery tested/loaded before you proceed with this recommendation. If your battery is good then either connections or alternator or the shift position switch. Before you start cleaning up the connections inside your engine well, please don't forget to UNBUTTON THE BATTTERY!

Once I get the boat back out I will report back in to see if my tampering with the connections helped.

What seems to happen in my simple layman's terms ( because I am not a pro but somewhat mechanically inclined and I pay attention to the motor), is that as you are getting on plane, your motor is under load and your alternator is not able to put out as much as it could say at 3000 or more RPMS. With a good battery and tight connections, it is designed to handle the needs of the engine. On top of this stressful time, midway to plane, you are likely trimming your motor combined with your hydraulic jack plate and the voltage is then dropping below a certain point with your bad connection and your motors computer notices and reduces power to the engine to avoid a more serious issue. Once you get above a certain RPM your alternator is working at higher RPMs and hence overcoming the poor connection you have in your system. Don't touch the trim until you get on plane and above 3000 RPMs and you will not have this problem. one day I was running down the lake and slowed down to barely on plane and it did it to me again as I was trimming for better planing at very low speeds.

Again don't mock be for the layman's explanation but this is my exact symptoms.

You most likely have a voltage problem. I will report back once i get the boat back out.

[03 202]

Not using any trim. Also new battery.

[Savage]

You are limited by guardian mode (2500 RPM) and the computer gives an overspeed fault, which means the computer thinks that the motor is in the neutral position (due to the faulty shift position switch) and is attempting to keep the motor from coming apart, when the motor is in fact really in the forward gear position...…..understand?

[03 202]

Understand completely

[Savage]

Just my best guess, let us know how it runs, after replacing the switch.....

[EuropeanAM]

I concur... Shift Position Switch (on shift slide inside engine cowling).

Simple confirmation: Unplug switch. You should be able to accelerate without difficulty (for TESTING ONLY, as you will have shifting difficulties without the switch).