454 mag mpi shutting down under load
 

Guys,

Im banging my head trying to figure this out. About to buy a scan tool. Twin engine boat but after a while and over 3k rpms the port motor shuts off loses all fuel; pressure, had a gauge on schrader valve. No sputter just quits. Pulled vst tank and cleaned screen. Swapped electric fuel pumps and same. Changed impellers and tstats to make sure its not overheating. Boat will run all day under 3500 rpms. When it does die, i but back to neutral then it starts perfect. Checked the map, tps and oil temp sensor. I'm pulling distributor and coil and replacing tonight. Check all fuses and relays as well. Anyone had a similar issue. all filter have been changed and its not from the tank because the other motor is fine. Only happens under a load. Running on the hose it will rev and never die. Any help would be appreciated. Boat is a formula 303 sr1.

Check for a one way valve on the tank pickup.

Wouldn't that affect both motors ? I'm only having an issue with port motor.

Each motor should have its own pickup in the tank.

So after the weekend. I got a scan tool had a code for nox sensor. Found previous owner did not reconnect the nox sensor. I replaced the sensor and connected the wire. Cleared the codes and the problem has not come back. I did run it over the weekend and the nox code is gone but it is displaying a code 42 &43. Code 42 is electronic spark timing fault and 43 is electronic spark control fault. I'm going through my connectors. I pulled the main harness to check for corrosion and clean the pins. It was missing a worm clamp, so I added that. Anything else to look for before i put it back in the water to test ? Also while i was out my temp gauge quit working in the same port motor. I haven't found any loose connections under the dash and the sensor on the thermostat is connected as well.

Check eng ground connections.

Found three separate issues, finally got a scan tool. 1st issue was the knock sensor, after replaced that and cleared codes and ran it and then an ignition code popped up. Removed the msd ignition system and installed mercruiser ignition and delco distributor. Finally I had no codes but the motor was still stalling out at high speeds. Finally after checking all the lines and fuel pressure found the electric fuel pump was working just enough to supply the vst tank at low rpm but not at high. Replaced the electric pump and boom runs like a champ. Hope this can help other people.