Sudden limit to 3200 rpm

[vickyb]

Hello,

I was on plane across the lake yesterday at 3900 rpm. Engine temp, oil pressure everything normal but suddenly both engines dropped down to 3200 rpm and no matter how high my throttle setting, they remained at 3200 rpm... seems some sort of protection kicked in... any idea? I do have half a tank of old fuel mixed with new fuel in both tanks

Thanks

[bud37]

Could be the fuel.......There are so many things here but considering the old fuel, it is possible the knock sensors may cut power.......can you put some good grade higher octane fuel in there?

Did you get any alarm warning ?

[vickyb]

I just bought the boat. Apparently the main tanks had fuel sitting for 3 years so my surveyor asked me to fill tanks to full (instead of draining them) and then run the boat and change the fuel filters after a few hours of running

[bud37]

An engine scan will show whether the engines have run with knock present , but like I said there are many possibilities here so don't focus on just that.....there should be many suggestions coming along.

How much fuel do you have in the tanks now ?......sometimes with old fuel it is best to get it out of there and have it disposed.

[vickyb]

Unfortunately, I filled up all 4 tanks and currently sitting on about $2500 fuel. Is there any video/tutorial that will teach me how to change the fuel filters myself? I have to take this boat 400km to my final destination (my home marina) and it would be helpful if I can figure out a way to do this myself so I can change the fuel filters 2-3 times as they burn through the old fuel

Thanks again

[bud37]

When it cut back, did you get an audible alarm ?? See if you can get the filters changed and watch how it is done.

[km1125]

First, you have to diagnose to see if it's actually clogged filters. If it happened at the exact same time to both engines, I'd be suspicious. You can swap to new filters and run it (and dump out the old filter or even cut them open to see what was inside to get more clues)

It's usually not hard to change the filters, but remember you are dealing with GAS, so you need to take all the precautions to avoid spilling ANY into the bilge and air it out when you're done.

If it's really gunk in the filters, a friend of mine rigged his with dual filters for each engine, with a valve to select which one the engine draws from. That was it was easy to switch over to the other filter and continue to your destination and change the 'bad' filter when convenient and in the safety/confines of a harbor or slip. With a multiple tank setup, you may be able to do something similar by having the filters before the tank switch and just by toggling to the other tank, you're running on a fresh filter.

[Viper]

When you change the filters, empty the contents into a white container and inspect what comes out. It can tell you a lot and may reveal the problem. If you have a lot of water in there, you should get it pumped out of the tank.

[vickyb]

Thanks everyone for all your help. Seems that the issue happened to be that the breakers for the alternators were tripped and the battery was dropping continuously till they could no longer keep the engines going at full power

[bud37]

Thanks for posting the outcome.