Sea Ray

Cummins engines seem to be more sensitive to low idle speeds than other diesels. Check the idle speed and be sure it is at least 750 rpm. Below that and the in and out of gear while maneuvering around a dock can cause the engine to die when put in gear.

This is an elemental first thing to check. From here the problem could be electrical or fuel delivery related, but if you have just run the boat and it dies when you get back to the dock pretty much rules out clogged fuel filters, etc.

Thanks for your comments. I will check the idle speed and hopefully that is the problem.

Check the specs for your engines from the Cummins site. Generally idle should be 650.

Idle is 650. More than likely you have a fuel delivery problem. When was the secondary filter changed?

Just a couple of ideas. Maybe long shots. If you are at 650 rpm idle that should be fine so check that first and if below that would be your problem. If not check fuel shut off wiring. Possibly some corrosion and when speed drops while shifting possibly you get a voltage drop that pulls solenoid to shutoff. This assume you have an energized to run system which I think it is. You could swap solenoid port to stbd. And see if the problem moves. It could be weak solenoid and with higher alternator output it is fine when idle is up. Another is a slightly tight cut less bearing or tight shaft packing. Although I think you would know it but make sure you have not picked up some line around that prop also.

Purchased a new to me a 2005 390 MY with twin Cummins 48os pulling out of a congested area, lo idle (550 rpm) selected, put the port shifter in reverse and when the boat continued straight, figured out the port engine had rolled back and shut down. Researching with SeaRay, the previous owner and Cummins revealed the following:
1. lo idle works, but as it is 100 RPM below the normal, make sure the engine has been allowed to warm up or stablized after running. In my case the engine had been shut down for an hour and while not a cold start, I rushed it. Now after start, I run the engines up for a couple of minutes at 800 RPM before selecting low idle and if approaching a dock I now have an awareness of the potential issue. Lo idle is supposed to be only 100 RPM under the regular idle. You might check what your regular idle really is.
2. What surprised me was the lack of a low oil pressure alarm. Searay told me that in 2004 ish the low oil pressure warning was moved out of the system monitor into the smart craft. additionally, around '04/'05 the warning was left out of smart craft. The wiring is there, but the smart craft isn't programmed. Just wondering if you got the low oil pressure warning when youe engine shut down?

Several things: Your RPM is too low. Lower RPM less = lower oil pressure in a hot engine that may be why. Fuel filter could be too. Depending on batteries acid flood are good for only a year and 1/2 to two years. I just replaced mine at 1.5 years. Dealer gave me credit but they were shot!.