Yamaha FX HO Misfiring?

JimS123

Admiral
Joined
Jul 27, 2007
Messages
6,240
2015 model with about 100 hours. It always started up almost instantaneously, even the first time after sitting all Winter. This year it cranks for a few seconds when cold, and starts up good when warmed up. I'm reporting this to show a difference in perceived performance, not necessarily a problem.

The last 2 times out after leaving the dock and accelerating up to cruising speed it would balk as though it was missing. The " sputter" for lack of a better term, was not continuous, but it would "miss" every 15 seconds or so. It After about 10 minutes it ran smooth for the rest of the day.

I got no alarms or warning codes. I don't have no way to personally check the ECM.

Any suggestions where to start?
 

QBhoy

Rear Admiral
Joined
Mar 10, 2016
Messages
4,805
Voltage regulator Jim. Have a check at this. Happened to mine. Sometimes be charging the battery enough and other times it would be intermittent and only getting to about 11.5/barely 12v. Isn’t enough to fire the fuel and it bogs.
Or it could be as simple as the battery, believe it or not. They break up easily inside and although can start the engine and appear healthy. Just aren’t good enough to operate well.

but for now, I’d check that voltage regulator.

good luck.
 

JimS123

Admiral
Joined
Jul 27, 2007
Messages
6,240
Interestingly enough, the battery was brand new and fully charged the day before the first episode. It isn't intermittent, it's only right at the start, just after launching. Within a few minutes it clears up.

I checked battery voltage with the engine running in the driveway. It looked OK, but obviously I couldn't run above idle. It idles in the water OK. The studder is only on acceleration.
 

QBhoy

Rear Admiral
Joined
Mar 10, 2016
Messages
4,805
I think you might have the 1.8 NA engine in yours Jim. But I know that most of the NA 4 stroke yam ski engines just don’t like low rpm for long. Certainly mine didn’t at all. Most time’s the voltage was a little low at low rpm idle when under load in the water. Meant that the ignition didn’t fire properly and not burn the fuel properly at that. Meant it bogged a little if it was ran like that for a while.
Other than that...just make sure there isn’t too much oil in it Jim and coming back through the intakes and bogging. Other thing to check is put a meter across each coil pack primary and secondary. Check it’s within spec at temperature. Could be that too. Throttle position sensor would be another thing to check. Check the idle on load in water speed isn’t too low also. Not too common on the 1.8l but also a leaking injector would cause this issue. More common with the older MR1 though. Caused by the ecu
 

JimS123

Admiral
Joined
Jul 27, 2007
Messages
6,240
After launching, when I come off the dock I usually run it for a minute or 2 and then accelerate up to about 30 mph (~5000 rpm). Its at this point that the missing starts. Once its warmed up it goes away.

I don't have any no-wake zones to contend with so it almost never is run at idle except for docking.

I have a measuring bottle so when I change the oil I know exactly how much to put in. The level is right in the middle of the range.

Thanks for the advice. I'll report back.
 

JimS123

Admiral
Joined
Jul 27, 2007
Messages
6,240
Someone suggested that 4-stroke 'skis are susceptible to spark plug issues and that they need to be changed frequently. I figured it couldn't hurt so I replaced them and it completely corrected the problem. Runs like a top and idles well too.
 

Farrela

Recruit
Joined
Jan 11, 2021
Messages
1
Thanks for the reply. Could you elaborate? You think the #2 injector is sticking open? Is that something that would happen intermittently? You're thinking it's the injector itself and not the ECU or the wiring? Is there any way I can test it without taking it apart?

I took out the #2 plug this morning and looked at it. I've attached a picture. It was wet and smelled like gas. This was a new plug that I put in yesterday and has less than an hour on it.
 
Top