5.7 Alpha 1 thunderbolt 4, randomly shut off at cruise
 

Hey all,

Have a 93 Ciera 2655 with an early alpha 1 gen 2 outdrive and a new (13 hours on it) 5.7. Full closed loop cooling.

Today I was running it at cruise ~3400 RPMs and planed out. Suddenly she lost power and stalled. Reset the shifter to N, cranked it and she fired right up. Got it going right back up to cruise and headed for the dock, worked fine. I had been running at low speed and high speed for about 1.5 - 2 hours prior to the stall - no hiccups nothing... This stall was super random. I have my kill switch/lanyard bypassed so it was not that. Boat has a new (sierra) coil for the Thunderbolt 4 ignition, new edelbrock marine carb as well as the latest trigger assembly in the distributor. New plugs (new freaking engine).

Any ideas?

the key switch might be the problem,pretty easy&cheep repair.

I had a 1990 5.7 with an Alpha Drive many years ago. It just quit out of the blue like you described. It took me a while to find it on the water but it was the shift interrupter switch which was located on a plate with the cable adjustment. It has a microswitch that momentarily kills the ignition when you switch from neutral to forward or reverse gear. I forgot if it was an adjustment or the entire microswitch was bad and I had to replace it.

Try this with key in on position and motor not running, at least on mine, the alarm horn is blaring. Soon as it starts up and builds oil pressure the horn stops blaring. So while its on and not running , start pulling fuses at the fuse block.untill the alarm stops. Either sand the metal on the fuses a little or put in new fuse. I have had that exact problem. Its like fuse had some corrosion and would intermittently lose connection. It too was a bayliner not that means anything but just saying. I would also ditch the seira coil and put in a Flamethrower 2 coil or a msd Blaster 3. Both have very similar resistance to original Mercruiser. Last and not least change the coil wire . Remember it fires 8 times for every 1 time a plug wire fires as there are 8 plugs and only 1 coil wire so it will wear quicker.

Chris.