Volvo 7.4L loss of power

[FMurphy344]

I have a 1997 Volvo 7.4L duoprop installed in a 28' Pursuit Denali. Regular service is provided by a mechanic. Kept having loss of power so he replaced the fuel pump. Seemed to help for a day or two, speed was great mid 20knot range. Now at 3000 RPM boat speed is 16-17 Knots. Over 3000 RPM (the tach is jumpy) the engine runs higher and consumes more fuel, lots of fuel. however the speed stays the same, about 17 knots. There is some knocking in the upper rpms. The engine feels rough just like it did before the fuel pump was changed. The props have been fine. Could it be the prop hubs or would it be more mechanical?<br />Any thoughts....Thanks.

 

[tommays]

Re: Volvo 7.4L loss of power

i am the clean bottom nut so i must ask its toward the end of the season what has built up on yours 3000rpm is 3000 rpm how fast was the bost at know rpm before<br /><br />fuel quality is big to hows your water sepator look, its best to carefuly poor the contents in to a bowl and look for water<br /><br />be very carefull about the knock if you can here it is a big concern boat motors burn pistons very quickly because of the heavy load on the motor you wont get away with it like a CAR<br /><br />tommays

 

[FMurphy344]

Re: Volvo 7.4L loss of power

The boat is still operating at its prior speed for the given rpm. It is when the boat is pushed beyond that rpm, the speed won't increase. The engine get louder, bogs down, feels slugish and rough. Just after replacing the fuel pump was replaced I ran the boat up with my regular passenger count, everyghing sounded good to the ear. Boat speed was mid 20's or maybe 8 knots higher.<br />I have been purchasing my fuel at the same place for the past three fill ups. It did feel funny the first time after I had purchased fuel and since.<br />The mechanic did take the filter off and didn't seem concerned about the fuel filter.

 

[Bondo]

Re: Volvo 7.4L loss of power

You have a Fuel Delivery Issue...........<br /><br />Somewhere Between(or Including) the Tank,+ the Carb.............