I have a  1995 2.5L 200hp Mariner EFI engine.  A couple of weeks ago, my ECU went bad and my motor wouldn't start, so I sent it to Simon Motorsports in CA and he rebuilt it for me.  I got it back Friday, put it on, and it cranked right up.  Well, I had a tourny at Toledo Bend today, so I brought my boat up and ran it Friday.  It took forever to start, it would smoke really bad, idle for a second, then die.  It did that probably 20 times before it finally reved up good and then it stopped smoking and ran great for the rest of the day.  Well, today, it did the same thing starting off...would idle for a second, smoke really bad, then die.  Finally it reved up good and it sounded good and stopped smoking, so I figured it was just bad gas.  I ran a few miles, then the alarm went off.  My voltage meter would jump from 11v to 15v for just a second and all my boat lights would flash really bright for a second.  I layed back down and it idled fine for a few minutes so I took off again, same thing, the alarm went of and voltage was jumping.  I then idled to a cove to fish.  I looked in the back of the boat and the red light was light on the system while the motor was running.  What could this be?  What does that light mean?  Is it water in the gas?  Or maybe my oil injection isn't working?  But why the voltage jumps? 

P.S.  It sucks to get towed back in 20mph NW wind in driving rain!

Sorry, but about the only way I can help you with your merc EFI is point you toward the gurus that know that motor.  You will have to register as a member first but post your question here  http://www.screamandfly.com/forumdisplay.php?20-Technical-Discussion.   A lot of these guys live and breath Merc EFI motors.

I see you are in central Louisiana and fish the Bend also. I can reccomend someone to you that just built my powerhead if you need him.

I have the same exact motor and year model. The same thing happen to me last year. I was told that it is a sensor (cant remember the name of it) that regulates the oil injection for the motor. I called the previous owner and he told me that it happened to him and that the sensor goes out every few years. The mechanic I brought it to told me that it would be better to disconnect the direct oil injection and put the oil in manually. It cost around $100.00 to have it fixed. I hope this helps.

I have a 1995 2.5L 200hp Mariner EFI engine. A couple of weeks ago, my ECU went bad and my motor wouldn't start, so I sent it to Simon Motorsports in CA and he rebuilt it for me. I got it back Friday, put it on, and it cranked right up. Well, I had a tourny at Toledo Bend today, so I brought my boat up and ran it Friday. It took forever to start, it would smoke really bad, idle for a second, then die. It did that probably 20 times before it finally reved up good and then it stopped smoking and ran great for the rest of the day. Well, today, it did the same thing starting off...would idle for a second, smoke really bad, then die. Finally it reved up good and it sounded good and stopped smoking, so I figured it was just bad gas. I ran a few miles, then the alarm went off. My voltage meter would jump from 11v to 15v for just a second and all my boat lights would flash really bright for a second. I layed back down and it idled fine for a few minutes so I took off again, same thing, the alarm went of and voltage was jumping. I then idled to a cove to fish. I looked in the back of the boat and the red light was light on the system while the motor was running. What could this be? What does that light mean? Is it water in the gas? Or maybe my oil injection isn't working? But why the voltage jumps?

P.S. It sucks to get towed back in 20mph NW wind in driving rain!

I would say that you have a stator going bad when the low side windings go bad on your stator it will be hard to start or it could be a switch box going bad ether on will cause your volts to jump around but i would lean toward the stator if your motor has all of the stock electronics on it you will have the 40 amp stator

and as far as the little black box under the efi system on the starboard side if that red lite comes on you have water in your fuel filter

and you can remove the oil injection and by all the parts for under 20$

if you need any more info let me know