454 mag efi at the beging of the day runs at 4900 rpms but at the end of the day it drops to about 4500 rpms help

Is your tachometer trustworthy? Are you going slower?

as far as i know my tac is reading right but i can tell the boat is a lot slower

Then the tach is probably correct. This sounds like something that's heat related, so it probably won't be that easy to pinpoint right away without the proper testing. Do you have access to a fuel pressure gauge?

I have to leave for work now, but I'll be thinking of things to check for you while I'm working today.

In the meantime there's some pretty sharp guys on here that will be helping you today.

something else when my rpms drops to 4500 the thottle level pushed all the way forword i can back it off to 3/4 thottle with no change to rpms could it be a tps breaking down if so is this a marine only tps or can i get one at a g m dealer if so would anybody have a part # on this thanks

Can you get hold of a scantool? If it is sensorrelated it will be a lot of guesswork without it.

talked to my mech this afternoon he said if it was a sensor problem the efi would go into a full rich condition but since there is very little black soot on the transom that is not likey the problem he suggested checking the thottle cable for binding also he said to change the plugs since the motor was rebulit last year that the mag engine was hard on the first set of plugs after a rebuilt or a new motor break in so i will try a new set of plugs come this sunday before i get wet will let everone know what happens thanks

Every TPS I ever took off a boat engine had a Delco number right on it that interchanged to that auto parts store's brand.

I would be reluctant to just start guessing and buying parts.

mats has the right idea with a scan tool.

Do you hear a misfire when the RPMs drop?

no misfire/ cutting out still runs &sounds smooth just lower rpms

"Sounds" like you're running out of fuel (low pressure,hot pump "slowing down""Guessing! BOB