2021 Merc. 115hp CT, sputtered again running about 4000 rpm?

[jlh3rd]

well....after yesterday, I'm sympathizing with you and looking for answers again myself.
This is a 2021 Merc. 115hp CT, purchased new.
I thought I had solved my issue.
Yesterday, it sputtered again running about 4000 rpm. Not a good feeling single engine on the Bay at 7 pm 45 minutes from my slip.
Early last year I traced a sputter to the corroding section of the feed to the ignition switch.....fixed , I thought.
Then late last year it happened again. So the filter was changed, it did look contaminated. I also added a fuel/water separator, pulled and checked my pickup tube and tank (absolutely clear even after 20 years) and replaced the check valve fitting...new plugs..thought I was good.
Then early this year coming back from Annapolis, it sputtered again. WTF.
So ran it back to the slip at 5-5500 rpms. No sputter.
There was a section of grey fuel line from the motor to the connector at the motor compartment then black fuel line to the tank.
I replaced that. This was in mid May. Been running all summer and no issue,...until yesterday evening. No water showing in my fuel/water separator. And I can't believe THAT filter is plugged...
Ran it at around 5000 rpm back to my slip....no sputter. 280 hours on the motor.
Vapor separator ?.....filter in the injector line?...(there is one, just involved to get to)

I'm all ears.

 

[airshot]

Are there more filters inside the cowling ? Often we change the obvious ones we can see but sometimes their are others inside buried that no one looks at. Just a suggestion here...

 

[Jeff J]

The only fuel filter I can think of on a Mercury 150 EFI isn’t visible. It’s accessible via yellow handle on the right side of the power head. PITA. It uses press-to-connect connections which helps with installation but can be a challenge to disconnect, especially the outlet hose.

 

[jlh3rd]

Are there more filters inside the cowling ? Often we change the obvious ones we can see but sometimes their are others inside buried that no one looks at. Just a suggestion here...

well, just jnside the fuel rail is one, but it's involved to get to. But how can I run 5-5500 rpm and no sputter if filters are the problem.

The only fuel filter I can think of on a Mercury 150 EFI isn’t visible. It’s accessible via yellow handle on the right side of the power head. PITA. It uses press-to-connect connections which helps with installation but can be a challenge to disconnect, especially the outlet hose.

that would be the first go to filter to change, yep.
I bet that 150 does have the fuel rail filter.

 

[Jeff J]

I agree with filter issues tend to be more consistent. Fuel pickup screens can get restricted and unrestricted as debris floats around the tank. The primer bulb should collapse if that is the problem.

I had a bad spark plug cause an intermittent problem on my Yamaha. It wasn’t until after I had spent a few hundred getting injectors cleaned and inspected, replaced one questionable injector and went through the troubleshooting tree a second time. The YDS was useless. Pulling plug and injectors leads one at a time with the engine running didn’t reveal anything. I finally found it when I tested the plugs in a full blown tester with a pressure chamber instead of just checking for spark on the engine.

 

[jlh3rd]

no primer bulb on my line. A 2021 doesn't need it.
pickup tube/screen checked, tank checked, new tank fitting with new check valve, new fuel/water separator, new, black marine fuel line. new plugs.
some sources are pointing to the fuel supply module (cha ching) .
You can't hear this motor at idle...shove the throttle forward and it takes off.
you cruise along for a month or two....then one day it decides to stumble....

 

[Jeff J]

I don’t know that any of the 4-strokes “need” the primer bulb but they are nice to have for troubleshooting and the rare occasion where there isn’t any fuel in the line. I have never liked running fuel pumps dry. Most I have worked on won’t tolerate it and are marked not to do it.

I have not had the pleasure of working on one but I have seen the inside of the fuel supply module. It’s much more complicated than the VST every other manufacturer is using. They can usually be repaired.

Do you have any way to look at the engine parameters when it is messing up or scan codes? The newer boats here have a maintenance page on the console display that gives limited information. I had thought about trying the dongle and installing the app on my phone for the older boats. The dealers couldn’t tell me anything about the system so I didn’t buy it and don’t know what it would show, let alone if it could actually be useful.

 

[jlh3rd]

I've got to find out exactly what type of fuel module I have. Preliminary searches show an older styled module was changed after 2018. That had 2 pumps in it and had a repair kit available. It also runs about $1300+.
I'm sure I have a VST...just gotta look it up.
I have a smartcraft tach but it's limited with oil, fuel pressure selections, water temp. When I run through the menu nothing shows up and of course there are no beeps occuring.
No scanner. I will run it in fuel pressure mode continuously the next time out, but then it probably won't sputter, right?
I think I remember stumbling across some device I can plug into my Merc. ( the plug is there) and send data to my phone. So there's that.

 

[Jeff J]

No scanner. I will run it in fuel pressure mode continuously the next time out, but then it probably won't sputter, right?
I think I remember stumbling across some device I can plug into my Merc. ( the plug is there) and send data to my phone. So there's that.

Ahh, the joys of having an intermittent problem!

That would be the dongle I mentioned. I don’t recall what Mercury calls it. I always wanted to try one but couldn’t ever figure out how much maintenance info it could provide to me. We are moving away from the lake so I’ll probably never work on another Mercury.

I hope you are right about the VST. Not much other than a high pressure fuel pump and a float valve in those.