1997 Mercury 150 EFI Intermittent Engine Alarm

[boatdonkey]

My engine alarm was intermittent at the end of last year, only when the boat was under stress - pulling a skier, or up at heavy RPMs for a period of time. I started up the engine this year, and had no problems the 1st day I used it. Second day I used it, after 30 seconds, the alarm behind the ignition key was beeping constantly. It was a steady beeping (as opposed to straight tone) and in some cases would do it if the boat was just in idle, and other times it would only do it once the boat was in gear? The engine seems to be burning oil, as there is some bluish smoke when I'm idling. HELP???

[blhdiscgolf]

Sounds like your getting air in oil line. Even though the oil is mixing there might be some air in the line and it causes the alarm to go crazy. I'm of course assuming gas and oil mixing chamber, and its not pre mixed.

[rodbolt]

has nothing to do with air in a line. the oil alarm on that motor is relativy complex. check the engine oil tank. if its low the alarm will sound. remove the cap, with engine running on premix, just in case, allow the tank to fill to just below the threads. if this solves your problem and no other leaks on the remote tank pressure hoses are there its solved. if the tank is full and the float switch tests ok with an ohm meter then its on to the tests for the rotational sensor. if those tests sow good try moving the green wire that goes from the alarm module to the outer switchbox to another cylinder post.. the alarm modules were prone to failure but a failing switchbox and sometimes a failing stator can trigger a false alarm. do all running tets on premix as the last common failure is the nylon oil pump drive gear. a quick test for that is to remove the pump and inspect it with a good flash light and eyeballs. the basic setup is an alarm for the taank level on the engine, and an alarm for the oil pump driven gear rotation. those signals are fed to the alarm module along with a signal from the temp sender. these are combined with the ign pulse signal from the outer switchbox. the module makes the determination of oil alarm, selftest with key on engine off or steady tone for overheat. I did not design it, I just have to fix them.

[verojoe27]

Boatdonkey, rodbolt has it pretty much covered. I had the same problem and after inspecting the oil pump worm and drive gears, I tried swapping the 2 switchboxes. My steady beeping alarm went off and did not sound again. The outer switchbox is connected to the low oil module and can send a false signal that makes it seem like the oil pump rotation sensor has detected that the pump is not working properly. You should test your engine with a 50:1 premix just in case it is your oil pump that is really failing. Hope this helps, Joe.

[rodbolt]

verojoe the switchboxes each have 3 output terminals to the coil primary of the bank of cylinders it controls. while the coil may or may not fire if the voltage output of the terminal the oil control wire is attached is out of spec the module may act up. can be caused by a defective box, a poor ground or a bad stator. that is why a thoughough test as per the service manual is in order, but the advice to do any further testing with a 50-1 premix is correct, just in case its aactually an alarm triggered by the rotational sensor. all the module wire from the switchbox does is let the module know if the motor is actually running or not, then it can make a decision to sound the self test or the alarm. otherwise it would alarm anytime the key was on and the engine off. but sometimes its as simple as the resevoir on the engine tank is a bit low. happens sometimes. especially engines that get started on the flusher and only run short periods then sit a while. the engine resevoir does not have to be very low to toggle the alarm and sometimes its at the level of just barely and any change in boat attitude and it sounds the low level, which sounds just like the no rotation.

[WillyBWright]

I just want to add that I burp the on-motor oil tank with the motor running until oil comes out. Every bit of air needs to be out of there or air expansion inside that tank under that black hood in direct sun can force the oil down far enough to allow the float switch to drop and sound the alarm. Just loosen the cap with the motor running until oil comes out. Then snug it up. Have a rag handy, but snug it as soon as you see oil and there won't be much cleanup.