oil alarm sounding
 

ok today i went out fishing and my motor oil alarm goes off but it doesnt stay on , it only goes on when i tach out above 3000 rpms and when it does go on it goes off then on then off but the fast i drive the more it stays on
what i did do is when i got back to the marina i took off the oil resevour and topped it off , it took about 8 oz i would guess i also topped off the oil tank but did not take my boat out after that what else could it be and what should i do next
\its a 1988 mercury out board 150 black max with the oil injection still working and i dont really want to remove it

I had a similar problem the other day with my merc. The top of the large oil tank was loose (my fault) so it wasn't pumping from the large tank to the small tank. I tightened it up and all was fine until I ran with the motor tilted up in shallow water. Tilting it was enough to make the alarm sound beacuase the level was still too low. I topped it off and all was fine. I suggest running it and checking to see if the small resevoir tank on the engine runs low again. Double check your lines and make sure the top of the large tank is secure as well.

Sounds like you are in dangerous territory here. Not trying to be a buzzkill here, but this sounds like a crank gear spinning at high RPM's. First thing to do is make sure you have 50:1 in the tank to avoid any engine damage while you figure out what is going on. Next check to make sure what is causing the alarm wether it is the low oil level, water in fuel, or no movement on the oil injection pump. Your symtoms though sound just like what happens when the infamous plastic crank gear begins to strip and the oil pump sporatically pumps. The low oil level should be a solid tone IIRC.

Here's some good info on the oil injection system. http://continuouswave.com/whaler/reference/mercuryOilInjection.html
You will hear a series of beeps when there is a problem with the system- low oil or pump failure. Since your resevoir was low that most likey caused the alarm to sound. Since you filled it up run it and see if that stopped the alarm. If so then you've narrowed it down. My guess would be if the pump was bad your resevoir wouln't have been low.

Ferm beat me to it, but i was going to say "get ready to premix"

same thing happened to me this summer(93 150 mariner). there is no pump to fill the tank on the motor. crankcase pressure is used to move the oil to the small tank on the motor. i ran the large tank low and the level dropped in the small tank. when i filled the large tank i didn't "burp" the top tank. took it to a local mechanic and had him check the pump, it was fine. he then told me about burping the top tank. i was out on the water when the horn went off, i keep a gallon of oil on the boat and dumped it in the fuel tank at the first sound of the horn. ferm and apare are right, make sure you are running pre-mix while troubleshooting problem..

and / or get ready to rebuild / replace

thanks for the replys and the web site , its very informative, From what i see there are only 2 things being monitored, the oil tank on the motor and the sensor for the oil injection system, it could be a bad module, so first thing i did was to fill up the tank, next i an going to take out the tube from the oil tank and make sure the screen is clean, than i hope its ok but if i have to disconect the injection system how do you do it? what are the steps?

remove the oil pump, pull the coupler out, then using a pair of needle nose pliers and pull the oil pump driven gear out, if you see melted plastic on the gear, you know whats going on. Pay attention to the coupler, it should fit loose within the hole, if its tight, you just found the cause. mercury finnaly figured out the coupler was swelling up and locking up the drive gear, they eliminated the sensor and went with a smaller coupler on late model 2.5 EFI's and carb motors

Spare, doesn't merc make a "kit" to eliminate the oil pump? with a plate to block off the pump hole. or do you just pull the shaft and leave the pump in place? also what about the oil feed line to the fuel system?