Guardian mode activation with no explanation from gauge

[chopper_bob]

Hello,
Apologize moderators, I started another thread on my issue as my reason for posting/title changed after further troubleshooting.
350merc B3, on 2013 Monterey 244fs, only 150 hrs, well maintained.
My question is, and it should be pretty simple to find an answer, guardian mode kicks in ALONG WITH CONSTANT HORN, with no explanation as to why from boat. Ive had it kick in 2x before, but the gauge told me afterwards (once for low block pressure other for low outdrive oil) why it tripped the alarm.

I see that there are essentially 5 reasons a constant horn will sound with guardian mode,
1) Low oil pressure
2) RPM Overspeed
3) Overheat
4) Low sea pump pressure
5) Low gear lube

Oil level and pressure on oil gauge are fine, I’m not over speeding, engine temp is midrange no fluctuations, gear lube level is fine, and it’s not low pump pressure.

So, my question is what is causing constant horn with no indications as to why on my gauge? I’ve replaced sea pump pressure sender previously, my guess is to change out oil pressure and temp sending units for the heck of it (again though, gauge would have flashed either two of those if that were the case).

 

[dubs283]

a computer with the proper software will be able to look up freeze frame fault codes and tell you what the issue is/was, otherwise is just speculation

 

[chopper_bob]

I think I may have stumbled upon something. While cycling through my LCD guage display, TRIM POSITION...Bad trim position sensors??? That would also throw on a constant guardian horn. Watched video on youtube that explains before trying expensive replacement, pull off trim position sensor cap and check for corrosion/good connection on copper swash plate. Gonna take a peek here soon.

What say you all?

 

[dubs283]

i doubt a trim sensor fault would cause guardian mode, it will cause a warning horn and set a fault if the boat is equipped with smartcraft and connected to the digital leads at the engine harness. guessing you have smartcraft gauges?

 

[chopper_bob]

Y

i doubt a trim sensor fault would cause guardian mode, it will cause a warning horn and set a fault if the boat is equipped with smartcraft and connected to the digital leads at the engine harness. guessing you have smartcraft gauges?

Yes smartcraft. Well, mech with code reader is stopping by this week. I’m grabbing at straws.

 

[dubs283]

you can check the setting of the trim sender(s) with an ohm meter. can't remember offhand what the value is but if you have access to either the manual for the engine or the smartcraft manual the set up procedure is outlined fairly well in both.

however if you are getting the trim sensor fault it may be faulty trim sender/limit, check and verify the sender is connected to the digital lead not the analog lead at the back of the engine

 

[chopper_bob]

So I figured out what’s happening is, guardian mode is activating because the boat is falsely sensing an overspeed condition and the engine speed limiter is kicking in, the engine throttles back and I can hear the 2 cylinders tump. I confused this with bad fuel flow or bad spark. (See attached chart I found.)

I am not over speeding and it kicks into this mode at random and even as low as 1500-2000rpm.
So, what would cause this? What sends the RPM signal? I read it’s tapped off ignition coil?

 

[dubs283]

So I figured out what’s happening is, guardian mode is activating because the boat is falsely sensing an overspeed condition and the engine speed limiter is kicking in, the engine throttles back and I can hear the 2 cylinders tump. I confused this with bad fuel flow or bad spark. (See attached chart I found.)

I am not over speeding and it kicks into this mode at random and even as low as 1500-2000rpm.
So, what would cause this? What sends the RPM signal? I read it’s tapped off ignition coil?

my guess is the in gear/neutral switch is either misadjusted or has failed. ecm thinks the drive is in neutral and will trigger rev limiter/overspeed fault even though the drive is in gear. switch is located on the shift plate

freeze frame history can tell you if there is/are faults pertaining to overspeed in neutral

rpm signal is created from the crank position sensor, ecm interprets data and sends signal to tach

 

[chopper_bob]

Update for my fellow boaters. Turns out my troubleshooting and research was wrong (yet again).

Was able to take boat into Merc authorized marina thankfully on short notice couple days ago. He called today, said stbd side exhaust gas running hotter at higher rpms than port side, suspects obstruction. Has to take off manifold and look.

 

[achris]

Save yourself all this drama in the future and get the Rinda Diacom software. You load it onto a laptop computer (it's not a phone app, thankfully ), plug the supplied cable to the engine and read the codes. Then you'll know without having to guess, exactly what the problem is.

 

[alldodge]

So I figured out what’s happening is, guardian mode is activating because the boat is falsely sensing an overspeed condition and the engine speed limiter is kicking in, the engine throttles back and I can hear the 2 cylinders tump. I confused this with bad fuel flow or bad spark. (See attached chart I found.)

I am not over speeding and it kicks into this mode at random and even as low as 1500-2000rpm.
So, what would cause this? What sends the RPM signal? I read it’s tapped off ignition coil?

Disconnect the in-gear switch, and if the problem stops, leave it disconnected

 

[achris]

Disconnect the in-gear switch, and if the problem stops, leave it disconnected

You need to disconnect it and join the harness wires together, or it will think it's never in gear.

And you can't leave it disconnected. The idle speed is different between in gear and in neutral. If it's faulty, replace it.

Chris.....

 

[alldodge]

You need to disconnect it and join the harness wires together, or it will think it's never in gear.

And you can't leave it disconnected. The idle speed is different between in gear and in neutral. If it's faulty, replace it.

Chris.....

Ahhh, no, in correct

 

[achris]

Ahhh, no, in correct

Yep, I was wrong. Open for in gear, closed for neutral.

But the rest, I am right. Here's the print from my own engine....

 

[alldodge]

Idling at 600 shouldn't pose an issue