Our boat has a 2007 Volvo 8.1 Gi DP (engine serial number 4012210765). Today we took it out for the first time of the season and unfortunately had a problem. After warming up for a few minutes in neautral at idle speed we went out and got up on plane as normal. After cruising for one minute or less there was a momentary hesitation of power followed by a backfire sound. There may have also been a brief clanking sound, but not sure about that. After this happend we turned toward the dock at idle speed. Once I tried to pickup speed a little, but the engine struggled so I backed off to minimum idle again. While close to the dock a squeeking sound started coming from the front of the engine. Upon reflection this may have been an alarm, but the temp gauge was normal. Oil pressure was registering too, but I don't remember the level. Back at the dock, the alarm/squeek would go away in neutral at low RPM, but would come back when engine speed was increased. The engine would also struggle at RPMs above 1000, but sounded fine at 600. Other information that might be helful 1) plugs were replaced 18 months/39 engine hours ago; 2) the engine oil looked fine both before and after the problem; and 3) as I have done in previous years I tried to be very thorough with winterizing and drained the block and manifolds (with coat hanger), removed and drained the hoses on the water pump, added antifreeze, and even used a marine grade engine compartment heater over the winter too (so hopefully a winterization problem is not the cause). If any of you can help try to figure this out I would certainly be appreciative.
. Thanks to him and sqbtr who responded to my question. One last thing that might be helpful to others, the squeeking or whining sound I was hearing was not the engine alarm, but a sound that the fuel pump was making when it wasn't working.