I just had my engine rebuilt last month and the shop doing the installation cannot seem to figure out why the MAP drops off and the engine shuts own as soon as I hit 3000 rpm (under load only. Seems to run fine on the trailer). What can cause the map to drop? I need this fixed...Ive already missed July and cannot miss August too....

Engine: 1994 Mercruiser 454 Mag EFI (385 hp)

--The company that did the rebuild has double checked the pistons and cam used and state they are exactly the same in terms of compression (piston) and intake/exhaust for the cam. (other than the pistons being .030 over). Cam timing has also been checked and is correct.

Nothing else was changed...HELP!!!

One other thing: right after I first got the boat back (3 weeks ago) it ran great (4800 rpm and over 60 MPH)...An hour into the day it started to run rough (like it was missing--The boat then ran at 3900 rpm max)...I took it to a shop and they told me we had a bad MAP sensor so they ordered one from CA...Ever since the new map sensor was installed the boat falls flat on its face 30 seconds into trying to get on plane (anything above 3000 rpm) and Im being told the MAP is low (6 inches of advance...My question is: if the wrong MAP sensor was installed when it was replaced could it be misreading the manifold pressure and telling the computer to shut down the motor? I just wonder because it did run strong when I first took it out (with the old MAP sensor)....Does anyone know the correct part number for the MAP sensor in a 1994 454 Mag EFI? Could this be the issue?

check the intake manifold,,,there is a tube that could be plugged,,the tube is used to get vacuum to the map sensor,,,had a very similar problem and also lost the first two months,,,