Help Weird loss of power 2800rpm to 3500rpm shift

[jasgent]

Hey all a friend of mine bought a boat. Its an inboard malibu that is having a problem. When he has the throttle in the full power position the engine begins to lose power slowing down and chaning from 3500 rpm to 2800 rpm every 5 seconds.

He has givin it a full tune up and replaced tons of parts to no avail. I thought it could be the prop cavitating, but he told me that the prop is the original prop and is designed for the boat.

I can get details on boat and engine specifics if needed.

Any help would be appreciated, as he is the only friend i have with a boat and I wann go waterskiing.

[RTS]

Fuel Pump...I also had the "porposing" RPM syndrome, at just about the RPM range you describe. A new fuel pump fixed it.

[jasgent]

Fuel Pump...I also had the "porposing" RPM syndrome, at just about the RPM range you describe. A new fuel pump fixed it.

What is the cost of a fuel pump.

Also, as an avid DIY mechanic I have always purchased the Factory manual for any car I have owned. I usually drop around $130 bucks for one of these. Is this done with boats also. Or are there online wiring diagrams and troubleshooting guides with the advent of our high tech internet?

Edited June 7, 2007 by jasgent

[RTS]

You'll need to let us know the specifics on the engine. My fuel pump goes for about $350 + shipping. I've got a service manual from Cymer's, but again, it's specific to a range of years and a specific manufacturer.

With your description of the problem, I'd bet a dollar it's a later model fuel injected engine, likely from Indmar. But let us know.

[chadwick02]

You'll need to let us know the specifics on the engine. My fuel pump goes for about $350 + shipping. I've got a service manual from Cymer's, but again, it's specific to a range of years and a specific manufacturer.

With your description of the problem, I'd bet a dollar it's a later model fuel injected engine, likely from Indmar. But let us know.

I just bought one 2 days ago. They are expensive!

[wienrdog]

First thing I think of for loss of power in that range is fuel filter. I haven't seen the up & down repeatedly with it, but that doesn't mean it couldn't happen. Much cheaper to try to replace that first. Also check fine filter screen at input to fuel pump. We've had 2 others with that problem this spring. Their symptoms were slightly different, but it's possible to see how it could cause they symptoms above.

If money's no problem, just do filter & pump at the same time.

Edited June 8, 2007 by weinrdog

[jasgent]

1992 Malibu Sunsetter with a rebuilt 5.7 liter MIegm350 V-8 Magnum tournament ski merc cruiser

replaced the fuel filter already?

[RTS]

I'm not familiar with those engines....I lose a dollar.