Mercruiser audible alarm

[Johnlons]

Here is another topic regarding the audible alarm.

I will start off by saying it is a 4.3L mercruiser TKS Carb engine. Serial number 0W631356

I have been dealing with this issue for a few years now. I randomly get the audible alarm while cruising. It does not seem dependant on RPM/Speed or anything.

Here are the steps I have taken:

Verified temp sensor was working properly by testing that the contacts close on high temp only. Also used an IR gun to verify the gauge was reading correctly (165 degrees) the last time out. Also checked exhaust riser temps.

Verified oil lube monitor was working correctly and even replaced it once due to a leak..

Oil pressure switch is new this year because i did not get the audible alarm with key in run position. Also tested continuity when I removed it.

I have tried cleaning and applying dielectric grease to everything including the ICM connectors. I have also unplugged and plugged the connectors back in which seemed to have worked in the past but not now.

Everything points to the issue being with the signal when it comes out of the ICM.

I did some testing and for some reason when the connectors at the ICM are plugged in, I will get a negative reading at the yellow wire at the temp sensor (connector unplugged from temp sensor) I hooked my multi meter to 12v at the battery and probed the negative of the multimeter to the black at temp sensor and get 12.4 volts and then when I probe the yellow I get 7.2. It seems as if the ICM is grounding it out some what.

The big question that I have is.... Why does the temp sensor run into the ICM via the yellow wire and then go to the buzzer with tan/blue wire. Does the ICM do something with temperature and timing?

Thanks

 

[alldodge]

The V6/V8 TKS motor has 2 temp switch's and a oil pressure switch. The TKS temp switch is used to supply 12V to TKS module after motor has reached operating temp. The TKS temp switch continues to supply 12V to module when motor is turned off, until motor cools back down.

The second temp switch is used to ground the Tan/Blue wire which goes to the ground side of the alarm.

The oil pressure switch has 2 wires on it, Yellow and Black. The Yellow goes to the ICM and Black goes to ground. So long as the switch is closed (no oil pressure) the yellow wire tells the ICM not to advance timing. Any grounding of the Tan/Blue wire will sound alarm and retard timing

With an intermittent alarm, first check that there is 12V (purple wire) on the alarm when the key is ON. Next take any of the Tan/Blue wires (lube bottle, temp switch) and ground it. With this wire grounded the alarm should sound

.

 

[Johnlons]

Alright I was mistaken on which temp switch. Im pretty sure I remember changing that one a few years back to make sure it wasn't the issue. I will test it again to be sure.

I grounded the oil pressure switch and the gear lube and it sounds the alarm. The temp switch with the tan wire pegs the temp gauge. What am I missing?

One my engine the oil switch for the audible alarm is only a single tan/blue wire. The temp switch is a single tan and the gear lube is one black and one tan/blue.

The second temp switch has a black and yellow wire. The yellow wire goes to the ICM. Is this a different set up than what you have described? I also have a tan/blue that goes into the ICM. Does the ICM look for a ground coming into it from the tan/blue or does it send ground out if there is a problem to activate the alarm? I'm a bit confused why the alarm could be activate if none of the switches (oil, temp, gear lube) tell it to sound.

 

[Johnlons]

This appears to be the wiring that I have. I have a seloc manual and its the diagram I was using to trouble shoot.

 

[alldodge]

In the 2 pics above I'm referencing the top one

The temp switch is a single tan

This is item 8 in pic and it goes to the temp gauge, it should not go to a switch

gear lube is one black and one tan/blue.

Correct this is item is item 35, but in the manual it has a misprint. In layout for 5.0 and 5.7 Bravo it is maked correctly

The second temp switch has a black and yellow wire. The yellow wire goes to the ICM. Is this a different set up than what you have described?

Item 26 is the oil pressure switch (Yel and Blk). If this is connected to the water jacket then its incorrect.

I also have a tan/blue that goes into the ICM. Does the ICM look for a ground coming into it from the tan/blue or does it send ground out if there is a problem to activate the alarm?

You have the TBV ignition and is connect by items 31 and 34. If one of the switchs grounds this sounds the alarm and tells the TBV to retard timing. If the module has a internal short which grounds the Tan/Blue ,then it to would sound the alarm.

Same issue happened with another in 2017

https://forums.iboats.com/forum/eng...m-problem-4-3l-mercruiser-tks-carb-2004/page2

 

[Johnlons]

Maybe I'm missing the actually temp switch for the audible alarm..

On the thermostat housing in the starboard side I have the sender for the gauge (tan wire) on the port side i have a temp switch with a water proof connector coming out of it (black and yellow wire) I believe its part number 866089. Am I missing the one for the alarm some where? I don't think it would even be possible for that wire to reach where the oil switch and sender are on the lower port side of engine. The oil switch for alarm is by distributor.

 

[alldodge]

Maybe lets go this route. There was errors in my manual, and there could be more. Do agree a connector up by the thermostat housing will not reach to the rear of motor, and much less down to low port side.

The parts break down for the motor shows a oil switch and pressure gauge sensor. These are normally down low, port side where the remote oil filter attaches or the filter is located if no remote is installed.

 

[Johnlons]

Its very hard to see back there but I have a sender and a switch. One with purple/yellow and a purple wire and the other on the sender is blue

 

[QBhoy]

Ok so apart from what’s said above and if you’re sure your gear oil header tank doesn’t have its float sinking or showing a false reading of you’re looking at the green stain line...when it happens at cruising speed...are you defo not underpropped and hitting the rpm limiter ? Just a wild card suggestion.

 

[alldodge]

Colors sound right, the Pur and Pur/Yel is its 15 (switch) feeding 16 (pump)
Blue for the Gauge

 

[Johnlons]

I have disconnected it while running before and still had the issue. Im thinking it's an internal ground short in the ICM. If this is the case, rather than buying a new ICM is it possible to eliminate the tan/blue out of the ICM and alternatively connect the temp switch? I'm still assuming the yellow wire is the signal into the ICM to tell it there is an overheat? Or is that just for the TKS?

 

[alldodge]

My Opinion
There should be no issue with disconnecting the Tan/Blue from the ICM. Only when there is a fault does that wire go to ground.

That said, if there is a fault (overheat, low oil pressure) then the ICM will not know, but ... the alarm will still sound off

 

[Johnlons]

So what purpose does the yellow wire coming from the temp switch do in the ICM? And does it actually tell the ICM to trigger the alarm?

The description on that part is THERMAL SWITCH, (Normally Open 130-110 degrees), Turn Key Start

 

[alldodge]

I really do appreciate this thread because its has caused me to dig into a few different manuals. In doning so I can see where the TKS manual I have is incorrect. The Yellow wire does go to the over temp switch and is there to signal the TBV, and also sound the alarm

So what purpose does the yellow wire coming from the temp switch do in the ICM? And does it actually tell the ICM to trigger the alarm?

The ICM does not trigger the alarm, the connection is there so it can tell the OCM there is an overtemp and also that switch also sound the alarm with a pass thru connection.

The description on that part is THERMAL SWITCH, (Normally Open 130-110 degrees), Turn Key Start

No, not right for that location. If that "type" of switch is in that location then once the motor warms up, the contacts close and will then sound the alarm and it will not shut off. That location needs a switch that only closes when the engine is over heated.

The TKS thermal switch is in position 19 and should close once motor reaches operating temps.

I have some drawings to redo

 

[alldodge]

Hope this make it a bit more clear

 

[Johnlons]

Interesting.. This issue is driving me crazy because I'm pretty confident that my engine is mechanically sound. I have done a lot of troubleshooting.

I have seen so many posts stating to unplug and plug the ICM back in and it fixes it. As I said before it did fix it but temporary.

The ICM does not trigger the alarm, the connection is there so it can tell the OCM there is an overtemp and also that switch also sound the alarm with a pass thru connection.

If its a simple pass through then I would think that tapping into the yellow wire and connecting it to the tan/blue that comes out of the ICM and then disconnecting that tan/blue from the ICM should work. See the attached picture for a better idea.
Do you see any issues with this setup? I hate modifying OEM stuff but man it seems like a waste to spend $400.

 

[alldodge]

I understand your comment, and while my comment was a pass thru, it was only in part. One part sounds the alarm the other retards the timing

The other issue, is your listing of the thermal switch and its settings. Those settings are for the switch in (Green) temp switch.

There is no need to modify the harness, can just unplug the connector, and jumper the 2 pins together. Doing this does not modify the harness but does allow the alarm to sound if there was an overheat

 

[Johnlons]

Your drawing in the last post looks to be accurate of the setup that I have. Would you mind posting the picture with the item description for future reference? My tach seems to be a little buggy. With the key in the run position but engine not running, the RPM's will climb to 4k slowly then jump back down. While running, its all over the place. I'm going to pull the gauge and clean the studs and connections before i move on with that. Makes me wonder if I have more going on with the ICM than just the alarm however the boat runs excellent.

I forgot to respond to your previous post regarding prop change and over reving. Everything on this boat is stock the way it came. I don't believe it was over reving because irregardless of rpm or speed the alarm is random and when I trim to high, the prop will "lose traction" and RPM's will raise but no alarm. As I have seen in some other posts lowering or raising throttle would make the alarm stop briefly.

Thank you for taking the time to help with the alarm issue.

 

[Johnlons]

The other issue, is your listing of the thermal switch and its settings. Those settings are for the switch in (Green) temp switch.

This is the description of part when I pull up the micro fiche my sensor does not have the pigtail attached to the switch. I'm not sure if they have updated it from the one I have but yeah it wouldn't make sense to me.

Without the engine running, I do not have continuity in the thermal switch. I remember testing it the previous season and it checked out okay at high temp. I will double check that again just in case it went bad over the winter.

There is no need to modify the harness, can just unplug the connector, and jumper the 2 pins together. Doing this does not modify the harness but does allow the alarm to sound if there was an overheat

Not understanding how this will work. The ICM will still be providing false alarm to the tan/blue if it is still connected to that circuit. I wouldn't be able to just unplug that one either because it has the purple wire for the coil.

 

[alldodge]

Not sure I can make a post as before because I need to change some info on it, but will work on it