Mercury Outboard 2017 150 Intermittent Missing

[cps22]

VERY intermittent problem continues for over a year, can't seem to identify the problem. The engine is a 2017 Mercury 150 4-stroke mounted on a Tracker boat. The engine has 240 hours on it and the problem started occurring at about 170 hours.

Symptom:
Motor runs great most of the times, however it intermittently begins to miss and sputter. It may run well for an hour or two, then begin to miss and sputter, I'll stop for a while and then the engine runs good again, sometimes for an hour or more, sometimes will miss again after 20 min.
Curiously, the engine ran symptom free for about 30 hours throughout the summer, then began the intermittent missing a month or two ago.

Things I've tried:
The intermittent missing seems like the engine is starving for gas so I installed a clear gas filter in the visible part of the gas line going to the engine so I can observe fuel flow. Although the fuel doesn't completely fill the filter, there always seems to be fuel moving through the filter, even when engine sputtering.

This has been an ongoing issue so have obviously run significant amounts of fuel from different sources as well as added fuel conditioner. Also tried new spark plugs and replaced the low pressure fuel filter inside the engine 3 times.

I took the boat to the dealer just before the 3 year warranty ended. The dealer checked the ECM and saw no errors or faults logged. They said the clear filter I put in the fuel line is likely the cause. I explained to them that I put the filter in the fuel line to help diagnose the problem. I wasn't impressed with the dealer although with the problem being so intermittent, it would be difficult without any ECM errors to guide them.

Again thinking the intermittent missing could be fuel supply related, I connected a 6-gallon auxiliary fuel tank thinking that it would eliminate the built in fuel tank, hoses, fuel demand valve, gas cap vent valves, etc. The intermittent missing occurred while running on this auxiliary tank too. So at this point I'm tending to believe that the problem is within the engine and not the fuel supply system. Again, this is very intermittent, sometimes I could run through the 6 gallon tank without problems, then next time it would begin missing. The 150 obviously would burn through the 6 gallons in about 80 min.

If anyone has any suggestions please let me know. The boat is out of warranty and I have zeor confidence in the local dealer so I'm on my own but luckilly experienced with most outboard repairs. I'm thinking of replacing the low pressure fuel pump or maybe a coil and moving it through the 4 positions. Again, any relevant information or suggestions would be very much appreciated.

 

[Faztbullet]

Does it just miss or does it lose RPM also?

 

[QBhoy]

Hi. You might think I’m daft..but hear me out and have a google afterwards of you like.
so my 2016 115 CT (identical gearbox to you) started an apparent miss exactly like this. I had the exact same thoughts as you too. Only occasionally. Sometimes as if it would stutter and lose power for a second. Especially as slow speeds and certain rpm. Annoyed the life out me. Changed filters and plugs. Even cleaned the injection rail filter etc etc.
Long story short...whilst changing my props mid season...I noticed that the white plastic exhaust bore seal ring or sleeve was lose from its designed location. It sits right behind the prop and when tilted up was floating out of position obviously. It has wee locking plastic tabs that are over time useless at holding it in position. When it comes lose occasionally out of position...it lets exhaust travel over the blades of prop for a split second and cause a momentary lack of drive and almost identical to an engine misfire. Honestly. Have a look at this. Sometimes it looks in position and sometimes it doesn’t. I’d put money on this being your issue. I had this last year...but I think by now it’s been well documented as an issue. I ended up sticking it in place with some sealant. Problem solved. Hope this helps. Have a google at least of merc 150 prop bore sleeve or prop seal ring. Sometimes called a blow out ring. Terrible design. Think that’s the term.

 

[cps22]

Hi. You might think I’m daft..but hear me out and have a google afterwards of you like.
so my 2016 115 CT (identical gearbox to you) started an apparent miss exactly like this. I had the exact same thoughts as you too. Only occasionally. Sometimes as if it would stutter and lose power for a second. Especially as slow speeds and certain rpm. Annoyed the life out me. Changed filters and plugs. Even cleaned the injection rail filter etc etc.
Long story short...whilst changing my props mid season...I noticed that the white plastic exhaust bore seal ring or sleeve was lose from its designed location. It sits right behind the prop and when tilted up was floating out of position obviously. It has wee locking plastic tabs that are over time useless at holding it in position. When it comes lose occasionally out of position...it lets exhaust travel over the blades of prop for a split second and cause a momentary lack of drive and almost identical to an engine misfire. Honestly. Have a look at this. Sometimes it looks in position and sometimes it doesn’t. I’d put money on this being your issue. I had this last year...but I think by now it’s been well documented as an issue. I ended up sticking it in place with some sealant. Problem solved. Hope this helps. Have a google at least of merc 150 prop bore sleeve or prop seal ring. Sometimes called a blow out ring. Terrible design. Think that’s the term.

UPDATE: Interesting, I think I may have "hopefully" resolved the issue.

After searching the Internet I found a couple of articles that referenced a batch of bad coils that Mercury had used that caused similar intermittent missing. It was the nature of the described symptoms that matched what I was observing, however the description of the coil was different than mine.
The 150 that I have has two dual coils, one for the top cylinders and one for the lower two. I purchased one from Amazon for $72 and swapped out the lower coil about a week ago.
Thanks to some above normal temperatures here in TN, I was able to get 8 hours of runtime without a miss. I'll get another four hours on today as the wife and I run up the TN River and one of its tributaries the Emory River.
I'm cautiously optimistic that the problem is resolved, howerver if not, I'll replace the upper coil. That would likely be next year as our warm spell is about to end.
Q8boy, thank you for the suggestion. If the problem were to return and then persist after the second coil I will definitely inspect the plastic ring. I noticed the ring as I changed oil as the drain plug is behind the prop on my 150.
Again, thank you to everyone for your comments. This is such a great forum to share knowledge and insights, especially on these types of intermittent problems.

 

[cps22]

Just an update..... I have put 16 hours on the Mercury 150 since replacing the coil and the engine has run great. Tennessee weather is cold, so I'm not likely to get more run time till early Spring. As I said above... I'm cautiously optimistic that the problem is resolved by the coil. Looking backwards at the problem it sort of makes sense. The ECM monitors just about everything within the engine. However, the output of the coil isn't sensed so that could explain why the problem persisted without causing any ECM diagnostic errors. Thanks again for the helpfuyl comments in the string. This forum is great!

 

[wifecallsmegrumpy]

ce replacing the coil and the engine has run great. Tennessee weather is cold, so I'm not likely to get more run time till early Spring. As I said above... I'm cautiously optimistic that the problem is resolved by the coil. Looking backwards at the problem it sort of makes sense. The ECM monitors just about everything within the engine. However, the output of the coil isn't sensed so that could explain why the problem persisted without causing any ECM diagnostic errors. Thanks again for the helpfuyl comments in the string. This forum is great!

CPS22, I wonder if you can provide an update. Did changing the bottom coil resolve this issue. I have exactly the same symptoms on a 2017 150 four stroke.

 

[jbcurt00]

CPS22, I wonder if you can provide an update. Did changing the bottom coil resolve this issue. I have exactly the same symptoms on a 2017 150 four stroke.

Start.a topic about your Mercury outboard.

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