Good afternoon. I'm new to this forum and hoping someone out there has heard of or has experienced the problem I'm going to describe. I have a 1997 SeaRay 330 with twin Mercruiser 7.4 MPI engines and Brovo One outdrives. The engines have 550 hours +/- and run very well except for a problem I will describe affecting the starboard engine. After the engines are warmed up and I have been crusing down the lake ( at 3700 to 3800 rpm, typically ) for 20 to 30 minutes, the starboard engine rpm increases, on its own, to the 4100 to 4200 range, stays there for 10 to 15 seconds and then settles back to the rpm previously set by the throttle control. This same thing will occure every 10 to 20 minutes thereafter until I reach my destination. When this first started to occure aproximatly two years ago, I initally thought I was having a cavitation problem because I had hit a rock earlier in the year. It was realitively minor but I did have the stainless prop trued up. When the rpm would increase, I would immediatly trim the starboard outdrive down and decreased the throttle and it would settle down until the next occurance. When the problem continued, I had the prop checked out by other prop shops but to no avail and the problem continued.
While it took me longer then it should have, about a month ago I decided to let the rpm increase and just watch it and see what happens if I do nothing. Thats when I noticed not only was the rpm increasing, but so was the speed ( measured by GPS ) by aproximatly 2 to 3 mph! So much for cavitation.
Since then I've tried crusing at a higher and lower rpm but it has had not effect on the continuing problem. I have also recently plugged in a Mercruiser diagnostic computer into the starboard engine and no codes came up when I plugged in nor when I was under way and experiencing the problem.
My current assumption is that there is a bad sending unit or something else electrical that manages fuel distribution to the starboard engine but that is where my diagnostic abilities end. Any thoughts are appreciated.
While it took me longer then it should have, about a month ago I decided to let the rpm increase and just watch it and see what happens if I do nothing. Thats when I noticed not only was the rpm increasing, but so was the speed ( measured by GPS ) by aproximatly 2 to 3 mph! So much for cavitation.
Since then I've tried crusing at a higher and lower rpm but it has had not effect on the continuing problem. I have also recently plugged in a Mercruiser diagnostic computer into the starboard engine and no codes came up when I plugged in nor when I was under way and experiencing the problem.
My current assumption is that there is a bad sending unit or something else electrical that manages fuel distribution to the starboard engine but that is where my diagnostic abilities end. Any thoughts are appreciated.