RPM issue with my port engine

Thestevedybowski

Thestevedybowski

New Member
Jun 17, 2019
6
Somerset, MA
Boat Info
2007 340 Sundancer
Engines
2007 8.1L Mercruiser Horizons with V Drives
Hello, 2007 8.1L Mercruiser Horizons here with 390 hours.
Lately my port engine wont get about 2800 - 3000 RPMs. It is running fine below that and very smooth but can not get above 3000 most times, even if I open the throttle wide.
Every now and then it will run fine like nothing is wrong but then go right back to it's old tricks.
Ran it with my mechanic while on the computer and it showed no issues.
Has anyone seen anything like this before?
 
You can read my 5 page thread about a similar issue, or you can go to the end, and start at the fuel management system. There are many stories about paint chips getting into the fuel and clogging the regulator filter or the fuel pump. Mine was a 20 year old pump was not meeting demand at high throttle levels.
 
Fuel is likely culprit, but don’t forget about your charging system. I’ve overlooked it on my motors twice now. First time it wouldn’t idle properly and timing seemed wonky. I thought it was iac, turns out the alt was toast and I was drawing off batteries. Idling on shorepower with the charger was masking the problem.

I’m also troubleshooting wot my other motor but I have an alternator for that one on the way before I dive any deeper. It’s making 11.5-12.5v at idle and then jumps up at higher revs but the ECM gets really weird with faulty voltages.
 
I have all new batteries end of last season, and the motor runs smooth. Very confusing.
 
Thestevedybowski said:
I have all new batteries end of last season, and the motor runs smooth. Very confusing.
Click to expand...

If it's not a guardian mode restriction then I would look to the fuel system next. At idle you using maybe 1-2gph but to get above 3000RPM your going to be needing 12-15gph and maybe your fuel pumps can keep up or there is a restriction from one of the filters.

-Kevin
 
Thus is a good list to check. But sounds like a fuel problem. What type of fuel cool you have. Cool fuel 2 or fuel cool 3. The 3 has the paint chip problem
Screenshot_20190530-164601_Chrome.jpg
 
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