Weird engine shut down last night 502 MPI
 

Last night while going for a cruise at about 60 mph, my engine just shut off, like someone turned the key off. No misses, coughs or trying to run. Just boom, shut off. Good thing I have two levels of exhaust stoppers for the rush of water coming off of plane with no power. Once I came to rest, and got the drive back into neutral. I tried a restart and it fired up normally. No issues the rest of the night through three tubing sessions, and one wakeboarding session. So I don't know.

I lifted the hatch and looked for something obvoius with a connector or something, nothing noted. My initial thought was something with the kill switch. I switched the kill of and back on quick at idle to see if it would catch or if it was a momentary and kill the engine either way. It just killed, it didn't stay running.

Any ideas other than perhaps checking my connections at the kill switch?

Could it be the neutral safety switch? I think if that is failed, the engine won't turn over at all.

Thanks for any ideas.

ECU on its way out?

my 502 does the same thing when im beating on it..... I seen many other posts about this same problem on the 502's no clear straight answer on the problem.

Most likely you have a short or bad wire somewhere. Probably a purple wire that is loosing connection or grounding out.

What does the purple wire signify?

I need to get the manuals for this engine and drive already.......

Would this shut down leave any codes that could be scanned?

My 454 blower carb. motor was shutting off occasionally, I cleaned the main wiring harness @ the engine with fine emery cloth wrapped around a small diameter rod with a drill motor and cleaned the male end. Then spread the male pins open slightly for a tighter fit. That fixed MY problem. Good luck with your boat.

Purple wire is "key on" power. It sends electrical power to everything.
Also check the main harness connection and make sure it is 100% clean and tight as stated above.

Check your main ground wires for any corrosion, I had a buddies boat doing the same thing last year. My boat started doing the same thing a few weeks ago. I replaced the ground wire and still no fix. After further investigating it turned out the alternator was only putting out 13 amps and once hot the volts would drop below 11 volts and shut the msd box off. The boat would start back up so it was confusing but I had been noticing the volt guage was reading lower than usual while running and at idle. You might want to check both.

Thanks for the ideas. I'm going to do some investigating this coming week. I'll report anything I may find.

Well, I did some poking around tonight, but have not really found anything conclusive. I did fine that the "start" terminal of my ignition switch is turning and is loose in the switch. So I'm getting a new one and replacing it.

Also, is the mercruiser emergency kill switch interupt the signal that you guys were referring to? I took a look at mine and checked the connections, which looked fine, but found that there was a purple wire coming off the switch that was cut off. the other two wires are being utilized, but no the purple. Anyone know what's going on here? I plan on installing a new switch just due to the age of it. Both this ignition switch and kill switch are original from '96 as far as I know. Could both be a source of an intermitentcy. Here is a link to the switch that i have installed: http://www.ebay.com/itm/MERCURY-QUIC...8465%26ps%3D54