I have a mild built 454 stroked to a 496 with mercruiser 502 EFI and A B&M 250 supercharger, Hooked up to the hose it seems to run excellent! But as soon as I put it in the water it has no power, wont even plane out? it coughs and chugs? I cant tell if its going into reduced engine power/limp mode or if I have any other problems? IM wondering if anyone knows how these modules that come with the blower work? what do they look at that would put them into reduced eng power? Ive played with different fuel pumps, made sure I have the correct pressure and volume, any ideas?

Look at two brown/tan wires at riser elbows...port and stbd. If sensor (s) bad, guardian. Look at oil psi sensor port side aft. Might be that connection there is sheet.

Oil psi and water temp are the only two culprits for guardian. Forget about the one on the tstat housing until you rule those three out.....it is digital...the other three....analog

Looking at the wire diagram I see the gear oil resivor is tied into the oil pressure switch wiring, so of the wiring is not hooked to the resivor tank would that put into guardian?

can you post a picture of your engine

So are you running throttle bodies on top of a 250 with a MEFI ECU?

Just curious

was the ECU reprogramed, are you running a MEFI1

He prob has the 250 blower with the mpi style plenum. Has throttle body but stil port injected

The throttle body in on the starboard side of eng in the middle above the valvecover! I uploaded some photos but I haven't figured out how to post them here?

Yes the ecu was programmed and the blower came with a purple module that I had to plug in! And the fuel pump plugs into that and that plugs into the mercruiser fuel pump connector

I have seen the setup that you are talking about, but really don't know anything about them.
I do not believe there is any "limp mode" in that system though.