Lost 400 rpms on both motors from one week to the next
 

Last weekend I was able to get my 496HO's up to 5000 rpms and this weekend I could only manage 4600rpms. This seems to have cost me about 3 mph and I am just wanting some feedback from you on what you think the problem may be. The temperature was exactly the same the previous weekend as was Saturday and Sunday.

-Shoe

Re: Lost 400 rpms on both motors from one week to the next
 

It this boat docked? Bottom growth can shave a few mph.

Re: Lost 400 rpms on both motors from one week to the next
 

Trim up? was the trim the same?

Re: Lost 400 rpms on both motors from one week to the next
 

The boat was not docked fromt the first week to the next and yes the trim was the same. I have no idea??? I have heard about the 496's having all kind of sensors going bad and only allowing so many rpms but I would think that this is not the case at 4600 rpms.

-Shoe

Re: Lost 400 rpms on both motors from one week to the next
 

More gas or people on board.
Props damaged
Is your speed via GPS or speedo?

Re: Lost 400 rpms on both motors from one week to the next
 

Approximately same gas(within a few gallons) and then later in the day it would have been less fuel this versus last. Same two people on board and there is not a ding on a prop. I may have gained a few pounds in a week but this is frustrating.

-Shoe

Re: Lost 400 rpms on both motors from one week to the next
 

Is it possible that you hit the rev-limiter last week-end and the engine is now stuck in safeguard mode - where it operates at 90%?

Re: Lost 400 rpms on both motors from one week to the next
 

rev limit does not go to limp mode. before starting the engine turn key to run but do not start, listen for 5 sec. for the warning beep to beep once then if you have a sensor falt ( causing power derating) then you will hear aditinal 2 or 3 beeps after the inital beep. I had a water pressure sensor go out and then a exhaust water temp sensor go out and this is what mine did.

Re: Lost 400 rpms on both motors from one week to the next
 

BBB is probably right. If the motor has a fault code in the ECM that is set and not cleared, depending on the code it can put the motor in a 90% only power mode which would account for the possible lost rpms and speed. Have someone or a dealer with a scan tool read the ECM and verify its running a 100% power level. Its probably a minor problem since your not in a fault mode that cuts power to 60% or 10% which is the limp home mode.
good luck,
Ray @ Raylar

Re: Lost 400 rpms on both motors from one week to the next
 

Thanks guys and I could understand that if it was just one motor but both at the same time??? I do have a buddy with a lap top and scan tool that plugs into the ECM. I will give that a try.

Thanks,
-Shoe