2003 mercruiser 4.3 efi throttle body injected alarm and engine shutdown at idle/neutral

[Kallen928009]

Okay I have a 2003 4.3 efi throttle body injected mercruiser that upon showing up to the lake will fire off easy and idle just fine to warm up after I push off the dock and toss in gear to head out I can almost immediately go back to neutral and it will run for 3 seconds then throw a steady alarm and engine will shut down it fires right back up and if I don’t bump up the rpms in neutral or put in gear (even at idle) it will throw the alarm after 3 seconds and engine will shut down 2 seconds later I have ran in in a tub at home and it will run just fine no alarms in and out of gear flawlessly (the issue only happens when in the water so exhaust has back pressure) once in gear it runs idles perfect zero loss of power. Temperature looks fine on the gauge ( 150-170) oil pressure looks fine (30-40) oil level fine ( semi fresh change 5 outings ago done over winter) coolant level good tried to flush thinking maybe got a air bubble somehow) I’m at a loss please help video was today 2nd time it’s happened and was shortly after pushing off the dock so engine wasn’t fully warmed up

 

[alldodge]

if I don’t bump up the rpms in neutral or put in gear (even at idle) it will throw the alarm after 3 seconds and engine will shut down 2 seconds later

I'm thinking oil pressure switch

Your motor has a oil pressure sender which is connected to the oil pressure gauge at the helm. The gauge is not connected to the Motors ECM.

There is also a oil pressure switch. The switch is connected to the ECM and if the switch closes, it tells the ECM oil pressure is low, sound the alarm and shut the motor down

So you either have low oil pressure or the switch needs to be replaced. It is most likely the switch. The switch and the sender in most cases are Tee'd together below the exhaust, port side rear of the motor

The pic shows a sender and a switch. This isn't yours but its close to what your looking for. If I had your serial number I could be sure, but most likely this is it. The smaller one is the switch and will look different on yours

 

[Kallen928009]

So doing more playing around if I wiggle the shift interrupter once the alarm sounds it will stop and engine stays running

 

[alldodge]

The shift interrupter has no connection to the alarm

What's your motor serial number?

 

[Kallen928009]

But if the shift interrupter is retarding the motor slightly could that cause low oil pressure

 

[Kallen928009]

And sorry I am not at the motor right now I can look and post the serial number later

 

[alldodge]

The interrupter causes the motor to misfire and slow the rpms. If it gets stuck it kills the motor. If your oil pressure is barely above minimum (around 6 psi) then it could cause it to go off