Engine alarm

[jwclbi]

I have a 1998 225 EFI Merc with a three alarm system, overheat, low oil, and water in the separator. Everything is operating fine, not running hot, plenty of oil, and separator is new. As well there is an inline 10 micron separator to pick up water before the engine separator. What the engine is doing is at low speed and idle, after warm up, the engine will miss and the alarm will make one beep at exactly the same time, for a split second. Then continue to run fine. As well once on plane and through full throttle it runs perfect. I disconnected the wire from the engine separator thinking it was triggering the beep but that didn't help. As well traced a couple wires that led to one of two micro computer boxes mounted between the spark plugs. Any thoughts? Thanks

[kmoose]

Sounds like and O2 sensor.

[77SceptreOB]

Knock sensor?

[eggsuckindog]

I don't think they have one -

if you disconnected the water separator it must be in the oil circuit, although I drain the separtor every now and then to check whats in it. Although since its only 1 beep apparently, it may be a glitch in the module itself, have you made sure the motor oil tank is dead full? Mine was giving a quick beep every now and then too, I went to the water separator since I had some in it a month ago- nope the oil tank was just a pinch low I guess?
On mine I'm thinking maybe take the main tank cap off to make sure its sealing correctly, as it would take a couple minutes to re-pressurize if its leaking down. Didn't appear low when I looked but must have been just enough to bounce, bled it an no issues.

[flyingfrizzle]

Sounds like you have a short in a wire somewhere. One other time it beeps is when the key is turned on, then the alarms mentioned. It could be loosing power for a split second and makes the beep at that time from a shorted wire or bad key switch possibly. I got the same motor a the house and have the book with the wire diagram if you need it. It shows alarm circuts...

[jwclbi]

Oil tank on the side on the engine is full to the max. I'll check the rest of oil system today after work. What i can't figure is why its only actin up at low speed and idle. In fact it will beep and miss at the exact same time for that split second as explained, and occasionally stall all together. Yes Frizzle you turn the key to the on position, it beeps, letting you know the system is active I believe. That seems to be working fine. If you have the diagram that would be great, looked online couldn't really find. My service manual only goes to 1996, than you.

[flyingfrizzle]

I will try to scan a copy of it for you tonight. I could be anything from a short to a bad sensor. Process of elimination is you best friend here. It may be difficult due to it being such a short beep and it only happens at select times but if you start at one point and go threw each alarm device and the wiring you will find it. I like to test the sensors and alarms on a used motor when I buy one to verify it all works. You can use a good meter to simulate an alarm in and out to see if the wiring is functional or not. The fact that it only dose it for a second will make it a bit harder to find but good luck!

[RidgeRunner]

If you have the three function gauge it should be telling you something when the horn sounds.

low oil - 4 beeps every two minutes and resets with engine/oil light illuminated
overheat - continuous beep with key on until temperature drops below preset level/temp light illuminated
over-speed - beeping sounds with reduced ignition timing/temp and oil lights flash alternately.
electrical sensor-TPS or engine temp sensor not functioning/temp and oil lights flashing alternately.
water seperating fuel filter sensor full of water- series of four beeps 2 minutes apart/fuel light illuminating constantly. Tested by removing from sensor and holding to ground for approx 30 seconds to hear the audible alarm

No knock sensor or O2 sensor on the 1998 EFI. But, there is a map sensor, air temp, TPS, engine head temp sensors.

The book says:
Rough Idle, Acceleration OK, Full Throttle Ok:
Improper EFI setup -- Unlikely as it is easy on the EFI
Failed Map Sensor
Coolant Sensor Fail
Broken Reed - Unlikely as the reed is in no way attached to the buzzer

Hope this helps. If you need any additional info let me know I have a book right here..Sensor testing is straight forward.. Dare I say easy.

[mnwnvc]

I had the in tank low (oil) sensor go bad on my old 70. Not an easy or cheap fix so I disconnected it. Warning was more constant than your problem.