5.0L alpha carbureted Intermittent Alarm

I have an 03 chaparral with a 5.0L carbureted mercruiser. The alarm is coming on intermittently. Mostly it does it when I'm at higher RPMs around 3000 or so and sometimes when I pull the throttle back from high RPMs. It is completely random, there is no sequence. When it does come on I can retard or advance the throttle slightly and the alarm quits. I have changed the temp sensor and the oil sensor. I have not changed the drive lube reservoir because I disconnected it for trouble shooting and the problem is still there. The only thing that seems to help is pushing on the connectors going to the ICM module which makes it go away sometimes but not always. It definitely has something to do with throttle position. All wires look good with no grounding issues. When it happens the alarm will not stay on long enough to open the engine cover to investigate. I have considered changing the ICM but they are very expensive and I would like to exhaust all other options first. Any ideas would be great. Oli pressure and temperature are within limits according to the guages.

You may need to have it scanned for trouble codes or take it for a ride w/the scanner attached to see if it can see the problem.

Thanks for the reply. It has the thunderbolt V ignition system which from what I've read, a scanner can only read hourly usage data. It does not give any type of diagnoses.

You have only so many sensors on the motor,

The wire color that feeds them I beleive is tan with a blue stripe.

1. There is the water overtemp switch (cooling system) Looks like the temp sending unit but different color wire.

2. the out drive oil resevoir low sensor, (gear lube monitor)

3. Oil pressure switch. located where the oil sending unit is. If you have an electric fuel pump then there may be two switches one that powers the pump and one for an audio alarm and the actual pressure sending unit for a guage.

You are omitting a lot of information so a diagnostics is tough.

At 3000 rpms, what is your motor temp? if iit is above 180 then that could be the root issue, should be below 170...

is the gear lube resevoir low?

Are you low on motor oil?

So you have basically 3 audio alarm switches.

I am not sure which beep pattern represents which switch. Maybe someone else can chime in with that info.

What ever the beep is coming from the issue needs to looked at as that is what the switches are for to warn of an issue

Have you done a new thermostat recently? If so did you use a Mercruiser "OEM" gasket number (27-530451) between the intake manifold and thermostat housing? if not then you may just be losing ground making the switch not work correctly do to the metal rivets in the gasket not making a complete ground path. This gasket goes on dry.

See Item number 10, click on part number to see a photo of the gasket.
http://www.mercruiserparts.com/Show...br=8182&bnbr=170&bdesc=Thermostat+and+Housing

Also if the oil switch get's blocked by debris, then that has been known to sound the horn at random RPM.

You could pull your oil filter and dump the oil in a clean coffee can then carefully cut open the filter if needed.

Change the engine oil while your at it.

Good luck.

Thanks for the help. I changed the thermostat last summer when I started having this problem. I used the the correct gasket and installed it dry. I am going to change the oil tomorrow and will check the oil switch. I checked the oil level today as kghost mentioned. It was right at the min line. Its possible the oil is missing the pump when i get up on a plane and at high RPMs. I have also moved the ignition module to a cooler spot. I keep going that direction due to all of the sensor wires go to that module. I'll be able to put it in the water Saturday and see if it helps since I cant get the alarm to do it while on the trailer.

Kghost, at 3000 rpm oil pressure and temperature are normal. Gear lube is full. The engine oil level was at the min line. It's possible that's my problem. There is no beep pattern for this system, when there is an actual problem (overheat, oil pressure) the alarm comes on as a constant beep and does not shut off until the ignition key is turned off.

All the system alarm switches are NORMALLY OPEN. When they are made they close and the ground path is now true.

So What I would do is remove one wire form one alarm switch at a time to see which one is causing the intermitten alarm.

ALso you say there are many alarm wires going into the ignition module??? How many? if they are not all in series then you would have different beep pulses......Try to count all of them and get back.

Also I did not say check oil level I said check gear lube monitor level, the small plastic bottle with gear lube in it. Is there water in it? that would also cause the issue. one thing you could do is with the key on, remove each alarm wire from its respective connection and simply short it to ground. Make sure each one is working and what beep type it has. I beleive there are three types of beeps, on all the time, a beep beep beep short pulse and a beeeeeep beeeeeeeep beeeeeeeep long pulse???? I could be wrong to how many and what pulse........been a while since I actually heard one that was on......

I was looking thru what I have for manuals and I do not seem to have your specific year manual. WHat I do have is the manual for 2 years prior, 2001,

It show a YELLOW wire going from the temp switch to the igniition control module for the alarm circut........
The oil pressure switch and oil lube monitor are tan with a blue stripe.

You may want to double check this.

Also is this a TKS system?? turn key start? if so then all alarms are tied together at one junction and what I said above wont all be true.

A bit more info please

Could it be a failed sensor?

I finally had a chance to get the alarm to come on long enough to trouble shoot which sensor is creating the alarm. The temperature sensor is the culprit but I just replaced it last summer, along with temperature sending unit. I just ordered a temperature gauge to ensure my temperature is reading correctly. If it is I guess I will change the temperature sensor again. Thanks for all ya'lls help.

Hello! I'm having the same problem: warning signal from the temperature sensor without reason. Replacing temperature sensor has solved the problem?

My boat 1998
To boat_tech: Your message box is full!

Thank's boat_tech for answer! I'll try to check the connectors Ignition Control Module at the weekend. Gasket thermostat I changed 2 weeks ago on a new OEM.
I noticed that the alarm depends on the trim of the boat. Lifting / lowering trim nose affects the appearance of the signal.
The signal appears when the boat comes on plane after 1-10 minutes. If I change a little-little throttle control - the sound immediately disappear, but may reappear. This is very similar to a bad contact! It remains a bit: only to find it...
And I hope that the problem is in the contacts.

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