2000 340 Sundancer - 7.4 MPI - RPM drops at 3000RPM

[Roger Williams]

Hello members,

Thanks in advance for any advice or input. Mercruiser 7.4 MPI. Full tank of gas ran fine on plane for our first part of our journey. Next stop tank nearing 1/2 full and notice that starboard engine at around 3K RPM starts to lose RPM and notice the engine sputtering and feel the difference (bogging down). At next stop, I changed fuel filter and noticed some crud and water when I poured out gas into jar. Replace with new filter and ran 12-14 miles and ran great. Thought problem solved, ya right! Next trip filled up ran again with no problems for 2.5 hours. On return trip fuel level obviously decreased and I notice the issue again where engine starts to lose RPM. Checked fuel filter upon return and fuel in filter looks really clean yet problem continued. The RPM comes back up but do feel a drop from affected engine.

Put on a scan tool and at with limited experience I am not getting any warnings aside from code 12 meaning it is in diagnostics I believe. I replaced fuel cooler on port engine but experienced very different symptoms in that case.

Here is a YouTube video showing RPM gauge of what I am experiencing. https://youtube.com/shorts/jFnkO-MWLh0.

Anyone have similar issues or suggestions on what may be at play here?

 

[Espos4]

No codes can usually be a fuel related problem.

second time you removed the filter you say it was only an inspection and sounds like you reinstalled the same filter.

Try another new filter as that seemed to work well the first time.

Is this a new to you boat?

 

[Roger Williams]

No codes can usually be a fuel related problem.

second time you removed the filter you say it was only an inspection and sounds like you reinstalled the same filter.

Try another new filter as that seemed to work well the first time.

Is this a new to you boat?

I have had this boat for 4 years with very few problems. It feels like a fuel problem and will try to change the filter again and keep with updates. Hoping that I don't have a dirty tank or other restrictions. My mechanic is skeptical of fuel as it runs fine at times but unfortunately the boat is a couple hours away from me and mechanic for the next month.

Thank you,
RW

 

[MJD]

Two weeks ago we were on a boat trip and one of our party had what sounds like similar issues, and initially thought dirty fuel, but on an older model Sundancer. The mechanic looked at it, checked the transmission fluid level and found it low, and unfortunately the transmission fluid was also milky. I am hoping this is not you -- but someplace else to check.

 

[Roger Williams]

Two weeks ago we were on a boat trip and one of our party had what sounds like similar issues, and initially thought dirty fuel, but on an older model Sundancer. The mechanic looked at it, checked the transmission fluid level and found it low, and unfortunately the transmission fluid was also milky. I am hoping this is not you -- but someplace else to check.

OOOHHH no sounds like a nightmare. I did check the transmission fluid and it is clean, the right level, and no signs of water. Thanks so much for your input.

 

[Roger Williams]

Changed to a new filter and not having problem but again have a full to half tank of fuel. Will report back after next leg of journey when tank is less full

Thanks