Engine RPM Significant Issue

[AZ Native]

So I just spent the last hour and half searching the threads to find something on my issue with no luck. So here goes:
I’m really frustrated with the intermittent port engine performance on my 2013 242 Limited. Max RPM on the Starboard engine can hit 7,500 at a lake elevation of about 1,300 feet. The port engine can only produce 6,000 RPM. Yes the cables are properly adjusted, yes the oil, plugs and air filters are fine and no I don’t have a cavitation issue. Here’s the kicker, when I started out yesterday heading across the lake the port engine suddenly jumped up to about 7,500 RPM WOT (joyous moment) matching beautifully the Starboard engine, for a long 15 minute run across the lake hitting 45 MPH with 4 big men in the boat. After stoping for lunch, the rest of the day I could only get 5,900 RPM out of the Port engine for max 30 MPH, although Starboard still will run 7,500 WOT. I do know that the throttle cables connect to an electronic sending unit that somehow manages the EFI. It’s like whatever is making decisions for the fuel rail on that engine is confused. I know nothing about the EFI and Electronics of the ECU but I’m hoping someone can weigh in on this mystery saving me an expensive and time consuming visit to a shop.

 

[Gym]

Hmm. What did you have for lunch? Just kidding. With something like this I would start with easy, less expensive possibilities first rather than starting with a brain transplant.

Start with putting Sea Foam in the gas tank as you may have a dirty injector. You may need 4 - 5 cans for a full tank of gas. (Read the lable). Next I would change the spark plugs. You could also swap with the good engine to see if the trouble moves. Remove the air filter to eliminate that possibility. Keep us updated on your progress.

 

[AZ Native]

Thanks. I will use the Sea Foam and change the plugs. Since the throttles are fly by wire, is there some kind of motor in the fuel rail that determines how much fuel to apply to the injectors? When the engine surprised my by revving to normal RMP for an extended run it seemed like something had just woken up or a sticky electric actuator had worked loose. The trouble with this kind of one thing at a time trouble shooting is you can’t just drive it around the block to see if the fix worked. It’s a half day trip to the lake. BTW lunch at the marina was BBQ.

 

[dzeppos]

You said throttles are fly by wire - is that an after market modification - as I thought only the 2016 SE+ and new have drive by wire setups?
The past few weeks, my engine at 1080 feet (lake mead) were running 7300port - and 7000-7100 Starboard - about 200rpm lower - might be need to change plugs (or bad gas) -its been 90 hours since I did a tune up. Your issue - are use sure (100%) nothing isn't lodged in there underneath that you can't see through the cleanout ports? Sorry - that's a headscratcher - if you don't have any luck - I"m seeing my mechanic next saturday (who's incredible about Yamahas and will ask him)

 

[mrcleanr6]

Sounds to me like one cylinder is dropping out. This could be fuel or spark related. Could be a bad coil, bad injector, bad ecu. When its not running right, have someone run the boat. Open the eng hatch and one at a time pull the wire/plug feeding each coil then reconnect. You should notice the engine start to run rough each time you do this. If you pull one and there is no change in how the engine is running then you found your bad cylinder.

 

[itsdgm]

Swap the coils from one engine to the other. See if the problem moves over too.

 

[Ronnie]

I lost a coil last summer and again on the other engine this season. My engines acted the way your engine is now.

 

[AZ Native]

Coil issue isn’t something I considered. Can’t be a single bad plug, the engine runs smooth as silk at 6,000 rpm. Could a bad coil explain why it suddenly ran normal for 15 minutes then after starting and stopping the engines it went back to only 6,000 the rest of the day?

I don’t know when Yamaha went to fly by wire but my 2013 throttle cables run back to a sending unit on each side of the engine bay.

Something else I didn’t think about, does each engine have a separate fuel pump and filter?

 

[Ronnie]

In my cases both the coil and the spark plug it went to went bad. The spark plug damage was impossible to miss a bad coil could be in pieces or look fine.

 

[Gym]

Could be a high tension leak on a coil. Check for burn spots on the rubber coil boot.