Misfire in cyl 1 then moved to cyl 6 - Gremlins in the system?

[IceyTys]

Hoping someone can help me out with my 2016 G21 H6. Last week I kept getting an error message that I had a misfire in cyl 1 and the boat kept going into limp mode. This week I tried to trouble shoot the problem on cyl 1, by swaping the plugs. I swapped # 1 and # 3 plugs........now its saying the misfire is on cyl 6, which makes no sense. For clarity i replaced all the spark plugs Summer 2021, so they are new plugs. Not sure if the wires are the original wires or not. Yesterday I had the boat out for about 3 hours and its was doing the error message at the very beginning of they day, but then the problem subsided and ran fine most the rest of the day. Pictures will show the error messages i was getting last week (cyl 1) vs this week (cyl 6).

Cyl 1 was last week, then Cyl 6 was this week AFTER I swapped plugs 1 and 3 to try to isolate the issue.

Question, I recently had to replace my flame arrestor and intake sensor....could the intake sensor cause this as well?

I did put some high mileage fuel cleaner in the engine at the last fill up as well.

What else should I be looking for here?

Thanks much in advance

[jpwhit]

Did you put the fuel cleaner in before the problem initially happened or after? I'm not sure I'd be putting fuel cleaning in a direction injection engine like the H6.

Are you saying you swapped the spark plugs? The spark plugs are rarely the cause of a misfire code on a single cylinder.

Failing coil pack is a pretty common cause, but that never moves around between cylinders. And a good way to diagnose coil issues is to swap coils between cylinders and see if the issue follows the bad coil.

Carbon build up on the intake valves can cause misfires on direction injection engines. Unlike MPI engines, where fuel flows over the intake valves, direct injection engines do not have fuel flowing over the valves to clean off the carbon. You can get carbon build up on the intake valves. In theory, this could move around between cylinders because it just makes the engine run rough in general. And the carbon tends to build up pretty evenly across all the cylinders.

Issues with the Camshaft driven mechanical high pressure direction injection fuel pump can also cause misfires that would move around between cylinders.

[IceyTys]

Did you put the fuel cleaner in before the problem initially happened or after? I'm not sure I'd be putting fuel cleaning in a direction injection engine like the H6.

Are you saying you swapped the spark plugs? The spark plugs are rarely the cause of a misfire code on a single cylinder.

Failing coil pack is a pretty common cause, but that never moves around between cylinders. And a good way to diagnose coil issues is to swap coils between cylinders and see if the issue follows the bad coil.

Carbon build up on the intake valves can cause misfires on direction injection engines. Unlike MPI engines, where fuel flows over the intake valves, direct injection engines do not have fuel flowing over the valves to clean off the carbon. You can get carbon build up on the intake valves. In theory, this could move around between cylinders because it just makes the engine run rough in general. And the carbon tends to build up pretty evenly across all the cylinders.

Issues with the Camshaft driven mechanical high pressure direction injection fuel pump can also cause misfires that would move around between cylinders.

Yes the fuel cleaner was put in BEFORE the issue, however I dont think that is the root cause, I just wanted to lay everything out there, by slim chance that was an issue. Additionally the boat just came out of winterization, so even thought the fuel cleaner was added, I cant reference back to earlier this season where it was running fine. I know about carbon build up and direct injection, I am an Audi owner...LOL. I am curious however, Audi makes a product specifically for carbon build up cleaning, any recommendations on PCM or other products that would help with carbon build up?

Yes, I hear what you are saying about testing coils, that would have been next, if the problem stayed on cylinder 1, after I swapped out plugs 1 & 3. Since the problem moved over to 6, that tells me it shouldn't be the spark plug, coil, or wires on that cylinder. So its probably more of a centralized problem. So maybe you have something with the fuel pump, I'll have a look at that. I know both fuel cell filter and pre-filter were changed at the end of last season.

[Scooter G]

I came across this Diagnostic Manaul a while back and threw in the bucket for future reference.
Maybe it might be of some assistance. Your fun starts about page 126...

PCM Diagnostic Service Manual.pdf

[IceyTys]

I came across this Diagnostic Manaul a while back and threw in the bucket for future reference.
Maybe it might be of some assistance. Your fun starts about page 126...

[ATTACH]n663900[/ATTACH]

Awesome....I'll get to looking....thanks much!!!

[jpwhit]

Be aware, that's the Diagnostic manual for the MPI engines. It doesn't cover the H5 and H6 direct injection engines.