450R nightmare - random shut down
 

(Update: Dealer finally thinks they have isolated the problem to a Mercury wiring harness)

Obviously if I'm asking here I'm desperate for answers the dealer and Mercury Racing can't seem to come up with.

I have 3 450R's on a 2021 Cruisers Yachts 38 GLS

Starboard engine started randomly shutting down 7 weeks ago. No codes, no nothing, just shuts off and sometimes no restart, sometimes restarted immediately.

Turns over fast (220 RPM's) but no start. (see more detailed description below)

In late June I was leaving a gas dock and looked down the the Starboard engine had shut off. I restarted it and it fired up immediately. Thought nothing of it... Then had shoulder surgery so didn't boat for 2 weeks. Boat ran fine for the last half of July and early August. Then problems started:

1st time it shut down I was idling down a river at no wake. 3 minutes after leaving marina. Limped back to marina and pulled cover, checked all fuses, nothing blown. Tried to restart nothing.
After about 10 minutes on the phone with dealer tried to start again and nothing... but accidentally left engine keyed on. Decided to check fuses one more time. When I pulled and replaced the first 2 fuses I heard a beep from the helm and was like "oh ****, forgot to key the engine off" so I went back and decided to try to start it and it fired right up.

Left dock and it ran for 10 minutes and shut down. Returned to marina and they pulled boat out of the water. While buttoning it up I pulled and replaced those same 2 fuses with the eninge keyed on and it fired right up (shut it down immediatly because I was out of water)

Next day dealer couldn't replicate problem.

Took it out for a sea trial 3 days later with them and no shut down. Took the boat out the next 2 saturdays and no shut downs.

The next Saturday took the boat out and it shut down 1 minute after I left the dock. I did the 'engine computer reset' the dealer suggested (key all engines off and put both throtttles in full reverse for 10-15 seconds) and then it immediately restarted. No problems for the rest of the day.

Dealer replaced fuel pump relay the following week at Mercury's suggestion

The next Saturday took boat out, cruised for an hour (mixed between no-wake and 3/4 throttle harbor crossing) docked for a couple hours at a state park and when I went to leave, no start. (fast turnover, no start). Did computer reset (both throttles full reverse with engine off) and no start. Raised the engine partway to pull cover and decided to try to start it before pulling cover. Fired right up.

Dealer replaced main power relay at Mercury's suggestion

Next Saturday took boat out and it ran fine for the first hour mixed cruising (some no wake and some 3/4 throttle runs across harbor). At no wake speed the engine shut down again. Tried to restart it without any other measures and it fired right back up. Ran for 3 or 4 minutes and shut down again but again fired right back up with just 1 attempt to restart. Ran fine for 3 or 4 minutes and when I left that no wake zone and went back to full and then 3/4 throttle to cross the harbor I felt a loss of power and looked at gauges. Starboard engine bogged down to 2200 RPM's (center and port were at 4,000 RPM's) for 3-5 seconds, and then seemed to recover and match the RPM's of the other 2 engines. Docked for 3 hours, and when we went to return to our marina, boat fired right up. Starboard engine RPM's matched other engine RPM's at idle but Starboard engine was spitting a lot of water intermittently out of the exhaust port (see video link)

(nevermind, can't post link until 10 posts)

Mercury recommended replacing fuel pump on Starboard motor and that was done.

Last Saturday took boat out... Cruised mixed driving (some no-wake, some 3/4 throttle) and boat ran fine for an hour +. Docked for 45 minutes and engine would not restart when we went to leave. Tried computer reset procedure, tried multiple times to start, nothing. Same thing full ignition RPM's (220) but no start.

Headed back to Marina at slow-no wake. Attempted to restart engine every 5 minutes or so. No start, only fast turnover 220 RPM's for a while then nothing. Was almost back to marina and tried one last time and engine fired right up. Decided to cruise around and see what happend. Cruised for another 1/2 hour then docked for an hour. When we went to leave dock to return to marina, no start just quick turnover. DID smell gas when we were trying to start. Tried everything. Tried computer reset protocol. Nothing. Engine DID almost seem to completely start once but shut off instantly (within a couple seconds) Pulled cover and pulled the fuses with key on like had previously appeared to work. After that not even a hint of starting. Nothing. Limped back to marina on 2 engines attempting to restart starboard engine every 5 minutes or so. Never restarted. Thats where I sit today.

If anyone has any ideas or knows someone who I could pay for some consultation please let me know .

The kicker... 'official' warranty period ended June 20, 2023. Literally about a week prior to that very first shutdown leaving a fuel dock.

Nik
New Berlin (Milwaukee) Wisconsin

I had a problem similar to yours....replaced wiring harness....fixed it.

I would try to run motor off of a remote tank and double check the fitting by the gas tank .

try jiggling the wires on the wiring harness
Every now and then you get lucky

I would try to run motor off of a remote tank and double check the fitting by the gas tank .

try jiggling the wires on the wiring harness
Every now and then you get lucky

By any chance did you have a problem with that same engine with oil blow-by from the supercharger?

My boat gets pulled out of the water and warehouse stored after each use. Sits inside til the following weekend. I have always smelled a distinct smell of oil from my starboard engine vents. A few weeks ago there was a small patch of oil that dripped down on the the ground under the engine. It appeared to come from one of the vent holes. Mercury said its "normal" unless its a lot of oil.

Engine oil level was on the high side of normal.

Since then I've been pulling the cover to check. No oil has dripped out like that one week. There has been a tiny bit of oil residue every week under the vent hold on the forward side of the engine (forward side if the engine was in the down position)

There is a loose or bad connection somewhere, big issue is where

Check fuel fitting and line all the way to tank... if it is sucking air it will lose "prime" and do exactly what youre describing... shoot me a pm if you want to know more specifics.

The appear to have located the problem. The wiring harness between the relay and the fuel pump... if they wiggle it while the engine is hooked up to the computer, the power to the fuel pump drops really low and fuel flow drops and almost stalls.

Given they already replaced the relay and the fuel pump, I'm bewildered why they wouldn't have, given the symptoms, tried this sooner but... At least its found now.

You guys are an incredible wealth of information! Thank-you all so much for the replies and I think I've found a much more educated group of powerboaters than I ran into over on THT.

I plan to hang around and learn some more. Truly thank-you guys!

NIk

Im glad you found the issue...while reading through your posting my first thought was an internal ECM problem and i was going to say to swap ECM's with a different motor and see if the problem follows to the other engine...at least that would have ruled out the computer if the problem stayed with the same engine.... :D

I was actually betting ECM also... Partly because when they first started with replacing relays I figured wiggling wiring harnesses would have been the first tactic...

This was a 7 week debacle... 7 weekends full of stress, taking boat out worrying about stalling at any moment. Trial and error, take it out the next weekend and have the same happen... and then repeat for over a month and a half... :( We scrubbed one trip to Chicago cause I didn't trust the motors. Scrubbed another overnight trip down to Kenosha.

Just glad I'll get a few more weekends before the season ends.

Thank-you again guys!