CONTINUOUSWAVE

On a 2014 Montauk 170 a 2015 Evinrude E-Tec 90 H.O. is mounted. When the engine is trimmed towards the upper end of the trim range, and when there is flat water, the boat will usually hit about 40-MPH. Sometimes, though, the engine will gradually drop speed to about 30-MPH. I will pay more attention to engine RPM the next time I am out. When it does this, the engine continues to run perfectly smooth, the drop is gradual, and later in the day or on the next outing we will be back at 40-MPH again.

What might be causing this?

It happened last season, as well, and there were no [faults] identified when the dealer hooked-up to the [E-TEC] diagnostic port to pull data from it. I don't think [the RPM loss in the E-TEC is caused by] a fuel restriction since it seems to come and go at random.

Maybe the engine was throttling itself back because of heat?

We have a water pressure gauge, and I haven't noticed any pressure [changes] when this happens.

The simplest explanation to explain a decline in engine speed that results in the boat speed dropping to 30-MPH from 40-MPH is a reduction in the throttle setting. Make sure the throttle lever has not just worked itself away from full throttle. It is very common for this to occur with remote throttle control levers.

I doubt that the reduction in engine speed is being caused by some action on the part of the E-TEC engine management module (EMM) trying to invoke S.A.F.E mode. S.A.F.E stands for SPEED ADJUSTING FAILSAFE ELECTRONICS. This mode is invoked when there are certain conditions, and it limits the engine speed to 1,200-RPM. See your owner's guide and the section on ENGINE MONITOR WARNINGS for more explanation. It is unlikely you could maintain a boat speed of 30-MPH with the engine in S.A.F.E. mode.

Do you have an engine tachometer gauge? When describing problems related to the engine operation, giving the engine speed is more helpful than giving the boat speed.

An alternative explanation for a reduction in boat speed to 30-MPH from 40-MPH could be a problem with supply of fuel to the engine. Check the fuel system for possible restrictions in delivery of fuel.

An alternative explanation for a reduction in boat speed to 30-MPH from 40-MPH could be a problem with spark ignition being lost in one or more cylinders. Check the spark ignition by using an in-line spark tester.

Thanks Jim, I am going to watch the tachometer the next time I am out so I can give better information.

Throttle lever has been at full throttle, that I have confirmed while experiencing the concern.

I should have thought of the fact that S.A.F.E. would limit it to 1,200 RPM. It seems like this is leaning towards a fuel delivery concern to me.

I will check the items you mention and report back! Thanks again!