I have a 1998 7.4 MPI Gen VI MEFI-2, Bravo III. Engine starts fine, idles fine, planes off quick, runs a minute or so then shuts down. Will start right up and does the same thing again. No problem with Idle as have to idle for 30 minutes plus to get where I can get on step and run. This is a fairly new ECM with 52 hrs. on it. No trouble codes on Test Tool. Temperature running about 165, Oil pressure 40 PSI+, Volt meter shows 14 volts. No hesitation or warning just shuts down. It would cut out on occasion but not shut down completely before today. But now it shuts completely down. I have also bypassed the neutral switch as that is what I thought was causing the cut out. Anyone experience this problem?

fuel - spark - voltage - you need to check all 3 to pin point the problem

your located where ???

scan tool with read outs, fuel pressure gauge, sealed inline spark checkers and a volt meter all for testing

When engine shuts down do you still have power to your gauges and other 12 voltage sources.

connections tight and corrosion free. Back side grounds, All battery cables and a strong battery. Voltage output when running is ???

fuel pressure when running and is it steady also what is it when engine shuts down ??? does it hold fuel pressure and hold fuel pressure after engine shuts down ???

When it shuts down is there spark and spark from the coil ??? how strong and steady is the spark ???

Run the engine on a portable fuel tank supply with a new fuel line and an outboard primer bulb hooked to your first fuel inlet fitting / barb engine side. This would be possible the first test to do. Did problem go away ????

If it just flat shuts off it is an electrical issue.

Spark should be fine, new plugs, wires, rotor and distributor cap. Alternator putting out 14 volts while running. oil pressure good and temp at 165. Starts quick, idles good, jumps on plane quick, soon as trimmed out I run for what may be a couple minutes and motor just shuts down. I do not turn the key to off position just starts right up. I will do a fuel pressure test as I did not have this problem before changing the fuel pick up in the tank and installing a new fuel line. I have run it on a portable tank while chasing a miss. Found the miss to be a bad spark plug. Did not have a problem before today. It seems like it is electrical as it is not like the fuel pump looses pressure and the boat starts to act like it is starving for gas it just dies. I know the ECM and system on this motor is sensitive so I will test the fuel pressure to see if a pressure fluctuation may not be sending a strange message to the ECM and shutting down the engine. I am pretty much at a loss for now. Any input is appreciated.

You changed the fuel pickup too? Like BUP said,I would run on portable tank or like I said earlier, get a fuel pressure guage and you can see what it's doing. If your new pickup is closing fuel line, it could be causing it to shut and fuel requirement at idle doesn't. Port tank will help isolate the pickup line.

What does it do when it dies and when you turn the key back on? Does it start up immediately or takes a second? Though its FI so it will prime up when you turn the key.

If your engine just completely shuts down without a spit or spudder like someone turned the key off very fast then IMO ECM problem of some sort.

Now if you get a stumble or 2 just before shut down ( like a stumble / spit then shuts down ) that can be fuel problem or a fuel delivery problem - even an anti siphon valve but then you say engine starts right back up so is that on the first crank or do you have keep cranking the engine over and over to reprime / electric fuel pump(s) running before the engine starts back up ? If the engine starts right back up very quiclkly without any problems, that is not a fuel problem.

A full script of exactly how your app shuts down and how quickly does it restart - within a second or 2 or 20 seconds ? What do you do to restart your engine - any throttle advancing ?

Do you have 12.7 volts min when engine shuts down ? I would check with volt meter. Monitoring the Scan tool will be very helpful while running down the water ways.

What ECM ??? Are you sure a MEFI 2 but a stock flash or who reflashed it if so ? A true MEFI 2 internal software was used on a L29 454 and the 350 mag only. Others were MEFI 1 software in a MEFI 2 case. Whats the numbers on your ecm ?

What ignition system is used and is it stock ???

Again IMO this might be a ECM or a ECM / ignition related problem - depends what you have here and the set up.

Shuts down like you turned off the key, no spit or sputter. I do not even turn the key to off position and it starts right up immediately, throttle in neutral position. Per volt meter in dash running 14 volts when shut down happens. This is true MEFI 2 purchased new from Mercruiser about a year ago. Has 52 hours on it. This engine is stock 7.4 MPI Gen. VI L29. It did not do this Thursday when I ran it but it was not running good due to bad spark plug. I changed the plugs Saturday which fixed the miss problem. Test ran today and it did the shut down thing. Looks like I will have to test run again to test fuel pressure just to be sure the ECM is not getting some message to shut down, Will also have test tool hooked up to see what it does and will run on battery #2. What ever is causing this is not random because it did the same shut down 3 times the exact same way but at different RPMs and it does not hesitate or act up from standing start to on full plane which seems to me would be pulling fuel harder than after it is on plane and trimmed out. It shuts down after it has been running on step for a few minutes. Thanks for the input, I am making notes of all and will try to eliminate possible causes one at a time.

Ok getting a clear picture better scripts written on all sides.

so it stalls running in gear then you pull back the throttle to N to restart the engine and it restarts right away - fast and easy like it should normally - is this CORRECT ???

I know I am all over the board with look at this and look at that but the facts on your end are getting much clearer for me to understand without eyes - ears - hands and feel on it so keep that in mind.

Man it sounds like a Neutral safety switch problem and or its wiring or if not possible a kill switch related problem of some sort. As you bring the throttle back to N to restart the engine - this clears the short and or the problem of some sort. Make sure your kill switch is not acting up as well. Sure sounds like a problem of either one.

I would check - Neutral safety switch and or the Kill switch. Check them very very closely. .

You probably have a Mercruiser commander 3000 control box / throttle as the kill switch is mounted in the lower side of the throttle / control box assembly. Hence why I would not rule it out as well or its wiring.

I thought you possibly had a reflashed ECM replacement installed. Just saying

Also does this problem show up only in rough water or no difference ?

here is what I think you have and the kill switch is incorp into the assembly and wires behind. The neutral safety switch is behind the assembly as well. pic below of the Mercruiser commander 3000 control box

http://www.marineengine.com/boat-for...3&d=1269716241

Already bypassed the neutral switch before test run so it is ruled out. Will bypass the kill switch also before I test run again. I am leaning to an electrical issue. One thing I will also check when running is the voltage from the battery to the ECM as batteries are old and may not be sending enough voltage even though the alternator is putting out 14 volts. I have not run it with the test tool hooked up. So hope all of these actions will produce some sort of result. Again thanks for the input. Will keep all posted.