3.0 Mercruiser quits abruptly

My 1984 Mercruiser 3.0 140 (1984 Wellcraft American)ran great for last 2 seasons until this year. First day out we went for about a half mile at 3/4 throttle and it quit right now. Almost felt like the engine locked up or vapor locked. It barely turned over at first and after 5 or 10 minutes it started ok. On the way back to the dock at around 2000 RPM it did it again. I've drained the fuel tank, it was clean, blew out the pick up tube, checked the anti siphon valve, replaced the fuel line, checked fuel pump for pressure and flow, rebuilt the carburator, installed new elctronic ignition, replaced the coil, spark plugs, set the timing, replaced all fuel filters. After all this it does the same thing. In fact, it will idle and run forever in neutral and up to 1500 RPM in forward gear, at 1800 rpm it quits abruptly every time. I can also run it in the driveway in or out of gear at any RPM with no problem. Anyone want to buy a boat? Forgot to mention that water temp. was good, 160-170.

Re: 3.0 Mercruiser quits abruptly

Did you bother to change the oil? Strain it when you do, and check the strainer device and the oil filter for metal. I would suspect, after your indication that it shut down, cranked hard and then started slow after 5-10 minutes, that you may have some issues with your valves or perhaps piston rings. Check your compressions and observe the operation of your valves (with the valve cover off). You may have something simple, like a collapsed lifter, or more insidious, like a failed bearing or rings.<br /><br />Also, are you sure your EST module is working correctly? Have it checked, too - even new ones can fail if not installed correctly.

Re: 3.0 Mercruiser quits abruptly

Thanks, I changed the oil last fall but will check the oil as you suggested. The EST is working fine. Idle is very very smooth, no miss or hesitation at all. After 5-10 minutes it turns over normally.<br /><br />I was told there's a fuel screen in the pickup tube line that can get plugged and cause my problem but I can't figure out how to get the line or tube out of the tank to check it.