Help with engine problem diagnosis please

[Evildwarf]

Changed the oil Saturday. 3.5 qts out, 3.5 qts back in, new filters...ordinary oil change.
Started the motors (1.8's) and the port motor is misfiring. (video below)
Never had a problem in the past. Checked levels all normal. Nothing out of the ordinary visually. All wires/harnesses tight. Took her out to see if running her a little would help...now it gets weird.
Port motor would jump from 5200 rpms to 6000 then drop back to 5200. Happened several times. It wasn't debris in the impeller, we get that a lot.

I have new plugs on the way but I don't know if that is the problem.
I'm not skilled with anything beyond basic DIY.

Any suggestions from you skilled remote mechanics would be a huge help. YouTube link for the video below

 

[PaulyB]

How does the air filter look?

 

[PaulyB]

@HELP

 

[tdonoughue]

First guess would be that you have a plug wire loose or something leading up to the pack. Check all of those that they are well-connected and didn't get pulled accidentally.

 

[Gym]

I'm guessing the plug wires are going to the wrong cylinders. Mine are marked 1 - 4. Make sure they go to the correct cylinders. I'm not sure if they labeled wires on the 1.8s.

 

[Neutron]

From the harness routing its nearly impossible to plug the coil packs incorrectly. There are no plug wires, just a harness to the 4 coil packs.
By chance is there an aftermarket hour meter attached to the engines?

 

[Murf'n'surf]

100% new plugs will fix it. That surge in rpm is a dead give a way.

 

[CDENsomnia]

Check the plugs and make sure they all look ok. I would agree with @Murf'n'surf the plugs are the problem. Pull them and visually check them. Make sure there is no weird oil or water residue.

 

[itsdgm]

What’s the recent history on the boat? Is this the first trip out this season after a long storage? It’s only one engine, right? How old is the fuel? Did you check battery terminals?

Anyway, good luck with the fix. I agree with the other guys, spark plugs would be one of the more common causes on an mr1 engine. Probably the 1.8 engines too if you haven’t replaced them recently.

 

[rkluck]

It sounds like you just changed the oil so I don't see how a wired can be swapped or loose. As mentioned above not sure how she was running or how long ago before this happened. My experience has been the spark plugs need to be changed. Let us know how this goes and/or a little more history on what lead up to this.

 

[Evildwarf]

if this were a medical evaluation I would say "no significant history"...
prior to oil change both motors have run like tops all season.
I got the plugs yesterday and will install ASAP.
Hope to report full recovery soon.
Thanks for all the info, this community is great!

 

[McMark]

Excercise the connection to the coil packs. There may be a bit of corrosion in one of the connectors.

 

[Gym]

In rereading your post @Evildwarf I think you may have a cracked spark plug. If the porcelain insulator gets cracked you can get a high tension leak to ground. If this is the case it would explain the RPM bouncing. I had this happen the first year I owned my boat. New plugs should resolve it.

 

[Cobra Jet Steering LLC]

1800 engines do not have plug wires and the oil change would not do this unless he overfilled the oil or damaged some wire harness plug accidently

 

[Evildwarf]

New plugs onboard and both 1.8's running like brand new...
Thanks for all the insight and info!
See you on the lake!