150 Optimax goes into limp mode, and full throttle just shuts down - please help!

[sintmaarten]

I live in Sint Maarten where there are no real Mercury mechanics. The engine has maybe 100 hours on it and is a 2008. Several mechanics have spent dozens of hours each on it over the last couple years, and almost everything has been replaced, including the CDI. The most recent mechanic had a real computer to plug it - wow!!! It showed Lo power (history showed that plus oil sensor and high speed alarm) He said the alternator was bad - it was only putting out 12V at idle, but 14 at higher rev. It did look black inside. So that was replaced, but still same problem. The oil sensor loses it's mind when it is like a quart low - and I can not angle the boat just before a plane like trying to make a wake - impossible. Yes, the sensor was changed. Might be a coincidence but seems to be running a bit rough after the alternator change, and whereas before the change I could open throttle to 5400RPM, but now not even 4k (before it screams and does a shutdown). Seems to be running a bit hot, yet water streaming out. I would love to throw this away in the ocean, and get a proper Honda or Yamaha but after spending everything I have on it (was supposed to be for a charter business) I can't. Please help!!!!!

 

[Chris1956]

Optimax motors are tricky and fragile, IMO. They have temperature sensors on the engine, compressor fuel pump and other places. The computer plug is the only real way to troubleshoot, and even those do not show all issues.

Since she goes into limp mode, I would look at the warning alarm guide in the service manual, on the boatinfo,no/lib/mercury web site. It could be as simple as an oil sensor or temp sensor saying the oil is low or the motor is hot.

 

[Teamster]

What size starting battery are you using?

I've know some people that have had similar problems using to small of a battery,

Maybe try the largest group 31 starting battery you can find, Borrow one to try if you can,...

Something cheap to try,....

 

[alldodge]

Voltage is erratic, things happen when boat leans prior to planning, may be running rough after ALT was replaced. I would start with the grounds, one is loose or corroded. When checking grounds make sure to remove the ends and bend back n forth. The bending can tell you if its something under the insulation. Then move to the connectors on the different components, check the pins. The big thing is it may look great, but upon inspection something may show up

 

[Dukedog]

The oil sensor loses it's mind when it is like a quart low - and I can not angle the boat just before a plane like trying to make a wake - impossible. Yes, the sensor was changed.

as it should.. keep topped off as much as possible

like said tha Battery size, condition clean connections.. very finicky in this area.. be sure check and clean tha male/female pin connectors.. check entire harness.......