RPM drops on one engine after it gets hose or floating water

[Dadsgotwake]

I first need to say how fantastic this site has been, I am now in the know that much that I'm dangerous as a boat mech.

I purchased a 2013 242 Ltd S about 5 weeks ago. took it for a service and the mech that did the work was full of crap, to be honest. the Port Engine is good and happy. the Starboard engine sounds a little rough. here are what's been done to get me to this point;

1) Proper Service by Yamaha Dealer has now been done (plugs / Oil / Filters Oil) Air filters have been cleaned and are good.
2) I found a stuck open injector after the crap boat mech so I then had them serviced, the fuel is now clean and good.
3) If you start the engine on the trailer and rev it up it'll go over 4000 rpm to 7000 rpm no issue without water cooling - yes I know but I am at that point in fault finding. no temp alarm is being given.
4) Start the engine then turn on the water cooling and rev it, you'll get maybe 4000rpm max and cavitation when on the trailer, it really feels like backpressure, to be honest. is this even possible from the cooling water in an exhaust?
5) in the water same issue as point 4 above.

both pee holes have water coming out, one more than the other so I am going to check the intake crate on the right engine

As I don't get it unless I have cooling water on the trailer or while floating in the dock I can't help but think it is some kind of back pressure within the exhaust system. I am also going to look at the jet pump but as it doesn't do it when I don't have water in then it seems less likely to be this I assume. Has anyway known of this.

One last thing, after the Yamaha Dealer looked at it and when the boat is low RPM and idle RPM's it's fine. He checked the piston heights and pressures and said they are normal and within limits. the boat has around 270 hours on both engine's

thanks in advance if you've seen this and can help.

 

[tdonoughue]

So, when you are on the hose and it only gets to 4k, you say there is 'cavitation'. Can you describe what you mean by that?

The reason I ask is that cavitation is a phenomenon where the impeller exceeds the maximum speed for the intake flow (and that max may be lower if the flow is turbulent), such that air is produced at the impeller edge and travels down the impeller (where the microbubbles burst and cause abrasion to the impeller). Since impellers don't push air very well (well, at all), cavitation then also causes a loss of power. And, usually, a bit of an increase in RPM (in fact, people will say it feels like the boat is 'slipping').

So, whatever you are feeling at that point is certainly not cavitation, because there is no water around the impeller to cavitate. But, clearly you are having something happening there. Is it a vibration or a sound or what?

If the same thing is happening on hose and on water (namely, 4k max RPM), then the issue is likely not the intake grates. Haven't heard of a backpressure issue in these boats (other than suspicions that high surfing ballast weights may put the aft underwater too far and cause backpressure that inhibits starting... but that is not your issue).

Oh, and, I would be remiss to not note: I see this is your first post! Welcome!

 

[Dadsgotwake]

Thanks, you’re of course correct in cavitation, I mean you seems as if the engine is vibrating a little.
Piston heights are all good, cyclinder pressure is good. I wonder if it is electrical. I took the rear exhaust apart and it’s all clear. Today with and without cooling water it was limiting at 4000rpm, which makes me now think maybe it’s electrical?

 

[tdonoughue]

Well, the stock, all-purpose advice for all rough-running issues on a Yamaha is to first change the plugs. So I will offer you that first. These boats tend to be very finicky about plugs and many weird issues with running are solved with new plugs (which are cheap to try as a fix). Plus the condition of the old plugs is diagnostic.

If that doesn't fix it, then I would check for spark on all 4 plugs. It may be that you are losing a cylinder (due to a bad coil, connection to a coil, etc.). So I agree with you checking the electrical. Failing those, a compression test is probably in order... Poor compression on a cylinder could also cause it not to fire. But we would know more down that road if changing the plugs you see something off in the old plugs that come out.

 

[Dadsgotwake]

Well, the stock, all-purpose advice for all rough-running issues on a Yamaha is to first change the plugs. So I will offer you that first. These boats tend to be very finicky about plugs and many weird issues with running are solved with new plugs (which are cheap to try as a fix). Plus the condition of the old plugs is diagnostic.

If that doesn't fix it, then I would check for spark on all 4 plugs. It may be that you are losing a cylinder (due to a bad coil, connection to a coil, etc.). So I agree with you checking the electrical. Failing those, a compression test is probably in order... Poor compression on a cylinder could also cause it not to fire. But we would know more down that road if changing the plugs you see something off in the old plugs that come out.

Thanks plugs are new, and the compression was checked by the Yamaha service tech recently and he tells me that was good. I’ll try the spark on all 4 plugs next.. again thanks for contributing !

 

[tdonoughue]

Wasn't sure if they had been changed after the injector was fixed. A stuck injector may have damaged the plug in that cylinder. But if they were changed after that, I agree no need to do that again. Compression should not have changed, of course--good that is not the issue, as that can be much bigger than electrical issues.

Let us know what you find.

 

[Dadsgotwake]

Hi I managed to inspect the plugs on both engines and they seem good, I also swapped the HT ignition coils from the left and right engine. at first, I thought it was running better so I gave it some rev's on the trailer - no water cooling and it seemed better. I then took it back to idle and it stopped itself. now the starter motor won't crank the engine so I am worried it has done something internally. I lost time to check fuses but the starter assuming that is what the sound is does try and turn so I thought maybe the fuses are good. Also, the power loss only seems to happen when the engine is warm after around 30-45 seconds from a cold start. I wonder if it is temp related with or without cooling water but something is getting warm and pushing pressure where it shouldn't..... thanks in advance to anyone that is able to offer a suggestion..

 

[tdonoughue]

Well, let's see. I think limp mode is usually 3k rpm. So it does not sound like you are in limp mode. Can anyone confirm the limp rpm as to this year?

It could be the thermostat, but then you would be getting overheat warnings (not so much putting pressure on things). You're not getting a little AL in the corner of a speedometer LCD screen, are you? Usually there is a really annoying beep too, but if something is wrong with your buzzer, you might not be getting that, i suppose....

 

[mrcleanr6]

When you checked the plugs did you notice any water on them? Possible head gasket leak or worse a cracked head letting in water while you have the hose on. There was a period of a year or two where the 1.8’s had a run if bad heads that were cracking. Not sure the years.

 

[Dadsgotwake]

Thanks for the replies, now just to compound everything the starter motor is turning but won’t spring out and turn the motor over. I need to fix that I guess. Old plug did have a bit of rust on them, but the pressure is good. I am more thinking now it’s temp related as it drops RPM one it is warmed up. Maybe a small crack opens or something. The engine does push out more fumes than the left one as well. I do have a AL on the dials, this is for the O2 sensor so I replaced this but it still does it which makes me think the sensor is working and the detection is real.

 

[Dadsgotwake]

I am really tempted to pull the engine out and bench it and look at it in detail on a work bench and get a deeper understanding of the issues

 

[tdonoughue]

I am thinking it is YDS time. Problem is you have multiple issues. Need to tackle them one at a time. If there were an overheat, you would not know it because you are already getting an alarm for the O2. The starter not coming out, rough running and stalling... Lots of issues.

YDS will show you all the codes and will allow you to clear them (as well as giving you all manner of other nice, crispy data). Problem is that I don't know that there is a YDS available for your year.

Anyone get YDS to work on a 2013?