MR-1 Misfire, smooths out when spark #4 disconnected

[wajetter]

My starboard engine (2006 AR230 HO) seems to be misfiring. When sparkplug #4 is disconnected, it smooths out the engine. Removal of other spark plugs one by one has very little effect - just a slight tone change. It seems that the least tone change is spark #2. Removing #2 is not noticeable, until re-connecting it.

I did some research and it seems like one of the main culprits could be the ECU keeping an injector stuck open. However, it is not clear if the main reason of the ECU issue is water intrusion. It appears mine has absolutely no water intrusion (see photo).

I opened the portside ECU box as well and it is also dry, to my relief. Tomorrow, I will swap the ECU from portside and see if it helps.

Should I look for wet spark plug after idling? Any other tips from experts?

Unfortunately, I have trouble connecting YDS to either of my engines. I think there is a misconfiguration to my Windows 10 Pro somehow. I heard there was a way to run some tests and hear injector clicks.

Video: IMG_4687

 

[wajetter]

Also tested switching the coils and spark plugs. Behavior did not change at all.

 

[buckbuck]

I have never been able to get Windows 10 to work the YDS. I keep an old Windows XP machine for working on the Yamaha.

 

[finnrigged]

Easiest way to know if your injector is stuck open is to remove the air box cover, remove the 4 Allen head bolts holding the 2 double spark arrestor covers on, pull them off, have someone blip the start key for a brief quarter second to actuate the fuel pump while you manually hold the throttle butterfly's open at the motor by actuating the butterfly's with your finger. Look down inside with a flashlight into each hole and if it is spraying fuel into one or more holes for more than a nanosecond (will probably spray 10 seconds or more if stuck open) then there ya go. This will work for u and is not dangerous if you aren't using an open flame for your flashlight LOL. Make sure all spark plugs and wires are installed when you do this so that you don't catch a spark the wrong way and you are good.

Regarding the ECM issue. Yes...No... Overstated so.... They can go bad BUT a MUCH more likely culprit is that you have a clogged fuel injector stuck in the open position. They can stick OPEN just like they can stick closed. If you swap your ECMs from left to right and the same injector sticks open.... Then it's a dirty injector! I've been through all of these issues and have rebuilt lots of MR1 HO motors. Thought I had a bad $600 ECM and it turned out to be a bad $25 injector.

 

[wajetter]

Update.
Turned out to be a misconfiguration of the carbs. Also, it seems some of the vent holes had some crud.
After taking apart the carbs, cleaning them, then tuning as per instructions, it idles well.
Injectors seemed ok. ECU had no signs of water intrusion.

Injector spray: IMG_4726

 

[finnrigged]

Not 100% sure exactly what you're referring to because there's no carburetors on these motors. Possible that what you're talking about are the throttle bodies if this is an FX140 or FX 160 motor... Or throttle body singular if it's a VX110 type motor in your boat? Regardless, glad you got it sorted out.

 

[wajetter]

Not 100% sure exactly what you're referring to because there's no carburetors on these motors.

Yes, I meant the individual throttle bodies. I got them synced - they were out of sync. Got used to a carb in my previous boat.

 

[kamilo2000]

What do you mean got them syncked?

 

[wajetter]

What do you mean got them syncked?

Each cylinder has its own throttle. They need to be synced mechanically to have as similar vacuum as possible. Pages 63-66 of service manual

 

[Beachbummer]

Sheet having followed the procedure, how do you think it got out of synch?

Thanks for sharing

 

[wajetter]

Sheet having followed the procedure, how do you think it got out of synch?

Thanks for sharing

I got this boat used. Also, I may have messed with the screws without knowing what I am doing and inadvertently got them out of sync. Well, I know now.