mercury optimax overspeed alarm at 4000

[downunder1]

Hi All my 90 hp optimax gives an overspeed alarm at 4000 and goes into guardian mode some times you can push through and then the motor will run ok and be ok for the rest of the day .. No error codes are set on the ecu my mechanic cant find anything wrong Please help

 

[Texasmark]

Re: mercury optimax overspeed alarm at 4000

SWAG: Your overrev module has a thermal problem possibly; intermittent at that from your comments. Possibly when at your mechanic's facility, the engine isn't hot enough to cause the problem.

I looked in my service manual (older engines) and it only explains that the purple wire is the rpm sensor and if exceeded the module shuts down the trigger modules via the yellow/black wire to the CDM's.

On yours, Merc may have maintained the color codes. If so, if you disconnect the yellow/black wire to the module and go out for a ride and if it doesn't cause problems, you found your culprit; the module.

You probably have an extra wire, maybe a tan wire with a colored stripe to sound your warning horn.

No reason why the engine wouldn't run with that module disconnected.

Just keep your eye on your rpm's.

Mark

 

[seashepherddelta]

Re: mercury optimax overspeed alarm at 4000

For anybody else in the future experiencing this overspeed alarm at 4000rpm

I have two 2006/2008 Optimax 90's on a 6.5m Delta RIB, and was given this overspeed alarm a few weeks ago. It would come and go and was inconsistent but slowly got worse and worse.

I had gone through a series of troubleshooting ideas. Fuel flow, water pressure, but ended on the Neutral Switch Sensor, which is located around the starboard side of the engine leading underneath the 2stroke oil tank. It is nearly impossible to access it without taking off the lower unit cowling, and lifting the oil tank up. This switch tells the computer that it is in gear, or else it will limit your revs whilst in neutral, without this functioning switch, there is no analog way to bypass it and achieve full power.

I fortunately have a spare engine which I was able to switch out this Neutral switch sensor and problem was solved immediately. It is a tiny black box, with two black cables, and a grey pin which when suppressed, tells the engine that it is in gear, allowing it to pass 4000rpms.
Now hoping Mercury will stand by their warranty and send me a replacement so i can have a spare, just in case.
In retrospect, it seems entirely trivial to have this sensor. Note: optimax are also equipped with a TPS- Transmission position sensor which ALSO tells the engine when it is in gear. If you disconnect this cable, you can start your engine but will not have any response if you attempt to put it into gear. What is the point of having both of these sensors? There are too many sensors on modern engines. If you dont own a diagnostic computer, or perhaps a spare engine, there is almost no way of troubleshooting or eliminating options if there is a fault in a sensor.