A friend of mine bought a 99 280 power quest in the beginning of the summer and it has just under 400 hours on it. Boat is equipped with a 454 mag (385 hp) fuel injected motor. He's running a 24p bravo 1 prop. This past weekend we were running a poker run (I was in my velocity) and he said coming across the lake his motor started dropping rpms when he was at 4600-4800. It dropped down to 4100 and wouldn't go any higher. When we made it back to the dock it was running a bit rough but would start and idle fine. I'm unfamiliar with the fuel injection on these, but I thought about simple things like fuel filter, fuel pressure etc. He pulled the plugs and they looked a bit rich from what he told me. He's planning on checking the compression and fuel pressure to get an idea on how the motor is running. Someone suggested he broke a valve spring, but I thought that would be odd seeing its a stock mag motor with under 400 hours. I'm sure it's possible, but I would think there would be more symptoms that comes along with a broken spring.


Air filter is good as well.

Any ideas on what we should look for is appreciated.

Thanks
Craig

Check the injectors too. If they lean out from clogging the motor will detonate and then timing gets pulled resulting in similar symptoms.

Thanks. I too was thinking the injectors could be part of the problem. He will have to pull them and send them out for testing? If so, any recommendation on who to send them to?

I would do a compression test next. I suspect he lost a cylinder. The question is why.

He's doing the compression test this morning so we should know something soon.

BAM Marine in Pompano Fl. has had VERY good reviews for their injector services w/ quick turn arounds and the benifits of cleaning to this level...

http://www.offshoreonly.com/forums/g...injectors.html

Similaer Issue I had end of last season. I found my compression was all over the map. Running rich, smell of raw gas. Ended up having blowen head gaskets. Lucky I cought it on time before more damage could be done.

Cause of blowen head gaskets = **** ass gas we have now days pluggin my injectors and causing the 502 to run lean. 6 Fuel injectors were "plugged", 1 was "so-so", and 1 was "good", said the injector cleaning dude.

You can youtube DIY injector cleaning and try to clean them your self. Other wise it is about $20-30 each injector for cleaning and flow testing.

I had a tuliped (sp) valve that did the same thing.
Also same symptoms before I dropped a valve seat, then destroyed the engine.