300 or so loss of RPM

[dpvandy01]

Hey all, I'm scratching my head here. Out yesterday on the 320 and I had an odd situation with my Starboard engine. First, 2003 320 DA with twin 6.2L Close Cooled Inboards. So while cruising at 4100 rpm my starboard engine intermittently drops to about 3800 and a feel a slight loss of thrust. Several seconds later it is back up to 4100. It is always a 300 RPM loss. This happens randomly but frequently enough to notice. every 45 to 70 seconds. Additional info, when I throttle up from idle it is smooth with no hesitation or variance trough the entire RPM range. When I idle both engines idle smooth, at 1800, 1900, and all the way up to 3200 (just on plane) they both run smooth and do not fluctuate. New fluids and impellers this season along with filters. If it were water I would expect it to happen through the entire rpm range correct? IAC? but that would cause idle issues right? Any thoughts? Thanks

 

[CliffA]

maybe an overly sensative knock sensor on the starboard engine?....if the knock sensor thinks the engine is knocking excessively it will slow the engine down to try and eliminate the knocking and save the engine....

or maybe the starboard engine does indeed have excessive knocking....might be worth checking into...

cliff

 

[Korkie]

Sounds like a sensor acting up. Had a MAT sensor act up on my 496 (2006). Had the same symptoms and also threw a fault on the SmartCraft. Turned out after a computer exam, the wire harness had a poor connection at the computer plug. When jiggling the main harness connector at the engine computer he saw a voltage fluctuation. The merc mechanic simply unplugged it, visually inspected the pins and plugged it back in, he used the words "re-seated it". Did the jiggle test and voltage remained steady at 5. Not saying this is your issue, but worth a try.