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Author Topic:   MERCURY Oil Injection Warning System
PdeMarco posted 04-05-2006 06:15 AM ET (US)   Profile for PdeMarco   Send Email to PdeMarco  
I have a 1992 Mercury 150 hp. I have experienced the buzzer beep beep going off without any apparent problem of starvation, rotor not working or broken shaft, lack of oil etc. My mechanic wants to try another warning module which will be my 4th new one fitted. Are there no reliable warning modules on the market that can be fitted to permanently fix this problem?

What other part could be contributing to this irritating problem?

Clark Roberts posted 04-05-2006 06:38 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
It could be a faulty buzzer. Not an easy replacement if buzzer is inside a control box but easy if mounted on harness behind a benicle control. Good luck .. Clark... SCN
jimh posted 04-05-2006 09:07 AM ET (US)     Profile for jimh  Send Email to jimh     
While there is a replacement system for the entire oil injection mechanism on your Mercury motor, I do not believe there is an after market substitute for the electronic alarm module. They are expensive, too! And from a small sample of owners that I know, that module seems to need frequent replacement. Two out of two owners with that module in their older Mercury motors have replaced it.

The alarm module on your Mercury motor connects to three sensors:

--cylinder head temperature sensor
--oil reservoir float switch
--motion sensor in the drive shaft for oil mixing pump

The first two sensors are just simple electrical contact closures, I believe, and it would not be particularly difficult to just have them signal an alarm directly.

The motion sensor is a magnetically actuated signal which detects the motion of the input shaft turning the mixing pump. The shaft has a a steel driven gear which is operated by a plastic drive gear clamped around a crankshaft journal. The plastic gear rotates at crankcase speed, and the gear reduction is very high, so the pump shaft turns much slower. The steel driven gear is coupled to a plastic shaft. This has a magnet set into it and glued in place. The spinning of the magnet poles produce an electronic signal from a sensor.

The plastic gear is in the crankcase area, and its only lubrication is from the oil carried into the crankcase with the fuel. If the engine temperature rises, as in a overheat condition, the gear is also subjected to temperature stress.

The electronic signal from the sensor is connected to the alarm module. The alarm module also receives pulses from the ignition module. The frequency of the pulses from the ignition and motion sensor are compared. If the ratio falls below a threshold level, the alarm module sounds an alarm.

This motion sensor was added to the system to detect failure of the plastic drive gear. Failure of the plastic drive gear was previously undetected, and it would cause loss of oil pumping and subsequent engine failure. The Mercury alarm system has no sensor which actually detects flow of oil. Thus it has no way to detect "starvation" of the oil, as you mention. It just detects two conditions: reservoir full, and input shaft moving.

rsess1 posted 04-05-2006 09:21 AM ET (US)     Profile for rsess1  Send Email to rsess1     
Jim that is very interesting and detailed information. You mention at the end of the thread that a change was made to detect failure of the plastic drive gear. In what year did they add this feature. I have a 175 efi 1994 Mercury and have had the alarm module replaced because of its failure so I am interested in the answer. I was told that the module was incorrectly signalling failure of the oil injection system by signalling a constant beep beep beep, as opposed to a steady beep.
jimh posted 04-05-2006 09:35 AM ET (US)     Profile for jimh  Send Email to jimh     
I do not know the precise history. A c.1989 service manual describes the magnetic sensor, so it must have been added prior to that epoch.
rsess1 posted 04-05-2006 10:37 AM ET (US)     Profile for rsess1  Send Email to rsess1     
Thank you for that information. It appears that I am safe at 1994. It turns out there are at least 2 different modules available. When my mechanic came to replace mine he had brought the wrong one. Apparently, if memory serves me correctly there are 4 wire and 3 wire modules that are not interchangeable.

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