396MY - Starboard engine shuts down - no reason

[TomO]

Thank you very much.
I am sending all of this info to the mechanic.
I appreciate it very much.

[tomschauer]

I would have them put a fuel pressure gauge on the rail while cruising. I bet you are losing pressure meaning the fuel pump / regular or both are failing. Don't try throwing parts at it while at the dock, unless you have more dollars than sense.

[Viper]

There are so many things that can cause this symtom. All mentioned above are valid points and possibilities. Even vapour lock is a possibility as the symptoms are exactly as you describe. To eliminate that as a possibility, try to duplicate the issue but leave the engine hatches off and cabin door and windows open when you go for the run.

Some fuel pickups had screens at the end of the tubes. If the tanks had solids in them, they would clog the screens starving the engine of fuel. After sitting for a while the debris would fall off the screen and the engine would fire up again but the problem would return. To isolate the engine from the boat's fuel system, run an external tank as mentioned above. Hook it up directly to the engine and recreate the conditions in which she's failed in the past. If she still fails, then it's an engine related fuel issue rather than the boat's fuel delivery system. Don't put the tank in the engine compartment, block off the fuel line from the onboard tank that you disconnect at the engine, and ventilate.

To eliminate the possibility that the ignition is cutting out, duplicate the failure and as soon as it happens, check to see if you're getting spark at the plugs. There are a few SAFE ways to do this. If you do get spark, then you've narrowed your search and can focus on the fuel system.

Finally, if the shop has the proper Merc diagnostic software, there are onboard tests they can perform related to the fuel system that can help determine things like failing or underperforming injectors. Not all problems will throw a fault code, so just looking for codes isn't good enough. If this has been going on for that long, these tests should have been performed ages ago.

It would help to check something if you post your engine serial number.

[tomschauer]

Viper, I would think vapor lock could prevent the restarting, but shouldn't cause the shut down while running under load, unless maybe like you suggest, something is restricting the flow to the fuel pump allowing the gas to flash due to a partially full fuel line.

[Viper]

Ya it can cause a shut down. As the fuel boils it becomes an aerated mixture. Depending on the type of delivery system, the lift pump for example then has a hard time keeping up with the high pressure pump's needs as it's now trying to pump a liquid/vapour mix rather than a full stream of liquid. She'll start running rough, get progressively worse, then shut down. She can probably run all day long at a lower rpm but not at higher ranges. Not the most common vapour lock scenario but it can/does happen.

If all that was done in terms of proper diagnostics is look for codes, then they've stopped short. They need to diagnose properly rather than throw darts and parts all over the place, that usually results in empty wallets, rich shops, and short boating seasons! Heck, have they done the simplest of things and called Merc tech support?? They can go through some steps that might help. But they better be prepared to provide some basic results for tests that would have been expected to be performed by now if they've gone through a service manual. Don't mean to throw anybody under the bus here, we may not be getting all the information, I just don't like it when shops throw parts at a problem without proper testing first.

[TomO]

Thank you for all of the suggestions. I will send them off to the boatyard.
The shop has the diagnostic software for the Merc engines.
They are actually talking to Merc I think at this time. I will also suggest they do so, if they did not. I appreciate the head’s up on this.

I will send the info to them this morning and I will be talking to them today.

I will post what I hear back from them. Hopefully it will be corrected shortly.

Thanks

[TomO]

All - Thank you for all of your suggestions.
My boat is back up and running well.
The problem - one wire that was coming from the wire harness to the ecm that controlled the amount of juice being received at the engines. The wire was fouled.
Once it was fixed, there was four test trips, then the final trip from Atlantic City to Cape May. The boat ran without a hiccup.
Thanks again,
Tom

[bud37]

Thanks for posting the resolution......with these newer engines with the ecu, the wiring and connections are more important than ever, great your guys caught that.......