Outboard issue

[Brknick22]

Hi, I have a 2018 mercury 115 on a 24’ pontoon . For the last year I’ve been having and issue where any time I’m over 4k rpm the engine lets out a few loud beeps then starts shaking til I back off the throttle completely . I can then throttle up again but can’t exceed 4k rpm. I’ve had it into the Mercury dealer twice already , first time they cleared the fault codes saying it was in limp mode and that would fix it which it didn’t then they changed the prop to a higher pitch and seemed to be ok for la few weekends but now it’s worse than ever/ any suggestions?

 

[ahicks]

What are they saying?

 

[Brknick22]

What are they saying?

They’d said the engine over reved which put it into limp mode . They said it was cavatating at high rom so they changed the prop but didn’t fix it either . My warranty ran out last month but hoping mercury will honor it since this issue has been going on well before the warranty ended/ at this point I’d pay a good mechanic to fix it because I have to creep up and back on the lake so it doesn’t keep having this issue

 

[ahicks]

If the new prop they installed was supposed to fix it, and it didn't, I'd be asking for a refund and my old prop back......

 

[jlh3rd]

you bought the boat....when?.....it had this motor on it?.....or how long have you had the boat/ motor combination.....Was it always doing this?... or did it just show up this last year....so it wasn't doing this the first 3 years?
....sorry....I like to know history before I make a comment

I have a 2021 merc. 115 CT on a 24' pontoon....what prop are you running?

 

[pwiseman]

High Rev Beep on Merc should be around 6K RPM. If I recall correctly it is one beep not several and it won't go into limp mode for a short overrev. If it ran fine for 3 years, you might be taking on water somewhere. Ran ok for a few weeks after you took it in and then started acting up again could be sign of a slow leak where over time you take on enough extra weight to cause some problems like this.

 

[Brknick22]

High Rev Beep on Merc should be around 6K RPM. If I recall correctly it is one beep not several and it won't go into limp mode for a short overrev. If it ran fine for 3 years, you might be taking on water somewhere. Ran ok for a few weeks after you took it in and then started acting up again could be sign of a slow leak where over time you take on enough extra weight to cause some problems like this.

View attachment trim.533A07DC-3E28-4023-AB53-C05CFC3DFB25.MOVHere’s a video I took last weekend

 

[pwiseman]

Here’s a video I took last weekend

It sounds like you are getting some cavitation once you get up to around 4100 and it gets worse as you go up. By change are you low in back end like I am? see the pic below.

At 4000 RPM, I would say you are moving pretty good and "limping down the lake" is probably overstated quite a bit.

underproping might be a cause, but it could also be over trimming, motor is just a bit too high in the water at that speed, or your tach is reading a bit low.

I have a similar rig which is a Harris 210 running a CT90 (21 foot toons). Basically a couple feet shorter with a few less HP and motor weighs the same as your 115. With 6 or so people it performs well but with 2 people I get some cavitation right around 4500 that is similar to what I see in your video. I am running a 13 pitch black max and it won't go up over 4900. My guess is I would have the same problem you have if I put a 12 pitch on.

Still working out what to expect from my boat in various situations, but it seems like the motor weight is a bit of an issue and the ultimate solution would be a jacker plate, which is overkill in my situation.

 

[Brknick22]

It sounds like you are getting some cavitation once you get up to around 4100 and it gets worse as you go up. By change are you low in back end like I am? see the pic below.

At 4000 RPM, I would say you are moving pretty good and "limping down the lake" is probably overstated quite a bit.

underproping might be a cause, but it could also be over trimming, motor is just a bit too high in the water at that speed, or your tach is reading a bit low.

I have a similar rig which is a Harris 210 running a CT90 (21 foot toons). Basically a couple feet shorter with a few less HP and motor weighs the same as your 115. With 6 or so people it performs well but with 2 people I get some cavitation right around 4500 that is similar to what I see in your video. I am running a 13 pitch black max and it won't go up over 4900. My guess is I would have the same problem you have if I put a 12 pitch on.

Still working out what to expect from my boat in various situations, but it seems like the motor weight is a bit of an issue and the ultimate solution would be a jacker plate, which is overkill in my situation.

I was by myself when I took this video , going around 16 mph at 4000 rpm. We changed the prop out earlier this summer and my max rpm with the lower prop is around 5k rpm. I used to be able to run the boat around 25-28 mph . With people on the boat I can only run about 14 mph before the beeping starts and engine shakes. I don’t touch the trim anymore since when I do it seems to happen more frequently, trim is always all the way down now

 

[jlh3rd]

Unless I'm missing something, your engine is not over-revving. so it isnt beeping and reducing power for that reason. My 60 hp merc didn't and my new 115hp merc doesnt start beeping until over 6100rpm . I'm guessing you are advancing the throttle, or trying to, past the 4000 rpm mark, it isn't the motor just doing it by itself, right?
So, It's not the prop. Could it be overheating?... a weak impeller that can't deliver past 4000 rpm but does ok before that ?...don't know what other issues can cause that, i'm sure there is a list...

BTW, 16 mph @ 4000 rpm is what I get also with my merc. 115 CT.

 

[Brknick22]

Unless I'm missing something, your engine is not over-revving. so it isnt beeping and reducing power for that reason. My 60 hp merc didn't and my new 115hp merc doesnt start beeping until over 6100rpm . I'm guessing you are advancing the throttle, or trying to, past the 4000 rpm mark, it isn't the motor just doing it by itself, right?
So, It's not the prop. Could it be overheating?... a weak impeller that can't deliver past 4000 rpm but does ok before that ?...don't know what other issues can cause that, i'm sure there is a list...

BTW, 16 mph @ 4000 rpm is what I get also with my merc. 115 CT

Correct , something is happening past 4k rpm when I throttle up. I’m guessing it’s either over heating or taking on too much water .

 

[pwiseman]

I was by myself when I took this video , going around 16 mph at 4000 rpm. We changed the prop out earlier this summer and my max rpm with the lower prop is around 5k rpm. I used to be able to run the boat around 25-28 mph . With people on the boat I can only run about 14 mph before the beeping starts and engine shakes. I don’t touch the trim anymore since when I do it seems to happen more frequently, trim is always all the way down now

I watched your video again and what you have is a 6 beep alarm. if you google that, you will find that there are a sorts of things that can cause it.

Sounds like bad sensor or lose wire and overheat is pretty common, but could be something more serious like low oil pressure.

The vibration might be due to motor protecting itself by not firing two cylinders.

You motor sounds very solid at 4K, hopefully nothing serious and not a total pain to diagnose.

 

[jlh3rd]

yeah, what he says......all suspect....vibration? I'd say cylinder deactivation.
maybe the bigger problem is the dealer......they should be able to diagnose that easily ( my opinion)...My understanding is that these engines set trouble codes just like cars, the dealer reads this and starts his diagnosis.......why can't they do that?....it aint the prop...
......So...i always start with simple basics....
spark plugs, fuel filters, ...checked?...impeller changed when?.....
it does not take but a few seconds for these engines to heat up and shut themselves down because of some cooling issue....
tough spot to be in.