8.1 Cuts out after 30 minutes

Hey all. Ive got a 2000 410 with the 8.1 engines. It will run just fine for about 30 minutes. Then port side started fluttering. Won’t die. Just cuts out. So I bring both motors back down to 2500 RPMs and everything is fine. Then after a while I will try to increase the RPMs and everything will be fine for a couple of minutes and then the same thing happens. We’ve replaced the fuel pump we’ve swap the coils and a couple other things. The mechanics are scratching their heads and don’t know what to do. I spent some money on this and I am looking for advice from anyone who has had a similar issue or knows of someone who has.

This sounds similar to an issue that I had a few years back with my starboard 454. After swapping coils, distributor caps etc it turned out to be the fuel line. Even though I had the CG approved lines that were supposed to be unaffected by ethanol they still degraded. After cruising a while it would lose RPM's & cut out. After several minutes it would start & if I kept the RPM's low it would stay running enough to limp back to the marina. It turns out the inner lining had seperated & collapsed when the demand created a negative pressure in the fuel line. Now, your problem may be different but, my mechanic was sure that it was electrical in nature too, until he exhausted all other options. Good Luck!

No Whistles, No Bells? Fuel. Had similar issue for 4 seasons, although mine would just vary the rpms. Be running and then the rpms would decrease by 350 or so and then go right back to where they were. They would just continue up and down at the 350 drop but never did shut down. Did filters, had fuel tree removed and cleaned as well as injectors professionally cleaned. No change. Removed fuel pumps and tested, both tested good. e discovered through all this we had the CoolFuel 3 paint issue. Applied to Merc for the parts. Merc replaced all the parts on both motor to include entire Coolfuel module with pumps and had my injectors re cleaned again. Problem resolved. Merc service manager suspects one of the fuel pumps, either high or low pressure, had an issue. If you are carbureted, maybe something going on there? Suspect fuel pump, maybe just cannot keep up.