Re: merc 5.7 MPI motr runs rough, stalls after running at cruise for less than 20 minutes

Originally Posted by
chs
hello all, this boat has been kicking my butt. it is a late 90's MPI motor( replaced some time in the past, in a 93 searay now) serial # ow029060. the boat starts and runs fine then you take it out and it starts running rough at top end, i can hear the engine pinging and it starts stumbling, it pull back on the throttle and from that point forward it runs rough. sometimes never making it back to the slip and stalls out. it wont restart for several hours.
ive checked the #'s on the scanner and the timing advance @ full throttle is between 28-32deg. no trouble codes, all gauges fine. this engine is non adjustable distributor. i have replaced the knock sensor and the coil/amplifier pack and yet still the same issue. all the basics have been changed, plugs, cap, rtr, wires. the fuel pressure is good @ 40psi @ full throttle. multiple ground cables installed, thinking it may have a voltage drop to the ecm. this boat has left me stranded multiple times , sea tow captain and i are on a 1st name basis. this engine has a lot of rust on it and it seems like every bolt is touch is rounded or frozen in place. even the bracket that holds the coild in place had to be replaced because the metal was flaking off and of course ,the bolts broke .
i am about to rip the einjection system out of this boat and just put a good ole 4 barrel quadrajet and thunderbolt IV system in place and be done with it, and yes i know there are a lot of other things to change as well.
thanks for the help guys
Engine is newer than late 90's.....
Find a good ecm from another engine, I have a few, so any good marina around you should have one you can borrow to test with. If you find an ECM to test with, drive your boat until it fails, swap the ecms and see if it restarts. You do not need to mount/ground it, just plug it in.
Last edited by Docksidemarineservices; 07-22-2019 at 09:51 AM.
Chris
Dockside Marine Services
Jersey Shore.
Mercruiser/Mercury Certified
Let the insanity begin.