Intermittent Alarm Beep - Mercruiser 5.0 V8 MPI

[bradiggy]

I'm starting to lose my mind on this one as nothing adds up. I've brought a 2000 VIP Vixen back to life and she runs great. Had a fun time rewiring nearly everything, new starter, new audio components, trim pump rebuild, oil change, gear lube change, etc etc, and have had a few great days on the lake so far.

That is except a phantom beeping from the dash. This occurs entirely randomly, sometimes even with just the key in / battery on / no engine (this one really baffles me). It predominantly happens while underway and on plane. Sometimes a couple seconds, sometimes 10 seconds. Sometimes won't hear it for an hour, sometimes its every few seconds running from spot to spot.

The beep while engine is off is the only reason I haven't started throwing every sensor/switch at it, and was hoping somebody here could point me in the right direction. Is there anything on these older engines electrical related that would trigger an alarm? Low voltage? Any diagnostics I can do other than unplug sensor switches (already tried gear lube res, oil pressure, and water temp and made no difference)

 

[Fun Times]

key in / battery on / no engine.

Just double checking, Key in or key on?

Engine serial number handy?

 

[bradiggy]

Just double checking, Key in or key on?

Engine serial number handy?

I believe it has happened with just battery on, no key involved, as well as key in ignition but not switched to run or start. This has only happened a handful of times, whereas when I am in the water with engine running idle or at speed, its almost guaranteed to beep randomly. Unfortunately engine serial sticker seems to have been removed but here's the cover.

 

[bradiggy]

On the chance it is engine temp related, I just ran it on the muffs for about 15 minutes and used an IR gun. I've read strbrd/port temps can vary but this is what I got. After idle and some revs;
starboard:
water pipe 110
manifold 155
riser 160
elbow 155
port:
water pipe 100
manifold 120
riser 100
elbow 100

 

[alldodge]

First the motor is not a MPI, it might be TBI but I'm thinking it's probably TKS carb

Remove flame arrestor and post pic of what's under it

 

[bradiggy]

First the motor is not a MPI, it might be TBI but I'm thinking it's probably TKS carb

Remove flame arrestor and post pic of what's under it

My bad, I thought EFI was the fuel injection and MPI was the carb version. Still learning!

 

[alldodge]

OK, its a Merc carb 2BBL not even a TKS

With beep sounding with Key off then there is something miss wired
Might be a bad key switch or prior owner buggered up the wiring that is causing the issue

If key switch is not removing power the it could be that's what's causing the issue(s)

With key OFF see if you can see any power on the + side of the coil

 

[Fun Times]

Looks like the usual Merc carburetor… The engine serial number should be on an aluminum type tag located just above the engine, starter, starboard, side, rear engine side.

If you’re hearing this beep with the battery on, and the key not turned, then it also possible there is another device inside the boat sounding the horn, such as a death gauge, fuel detection system in the bilge area etc. at least until it’s confirmed it’s the engine warning system horn usually located up under the dash area that should look something like this,

 

[dubs283]

Agree with FT. Check for a depth sounder alarm among other accessories

The audio warning system mentioned has a built in test for proper operation. With the key in the run position engine not running it should sound constant or at least for a few seconds depending on engine model. Key on, engine off the alarm sounds from a lack of oil pressure, easy test.

Try this test, confirm the audio system is operational, compare the tone of beep/horn/sound. If they are the same, there's the possibility of a short somewhere in the tan/blue wire in the engine harness or boat harness. If different its probably an accessory.

You mentioned performing a lot of wiring work and other items. Is there any chance you may have run a screw into a wire harness anywhere?

 

[bradiggy]

Found serial number tag; L653238. Can ya'll confirm exact engine name so I don't look dumb in the future!

As far as other comments go, it is 100% the audio warning buzzer pictured above making the noise (and this is the same buzzer that emits a solid beep when key is turned to run but engine hasn't started).

The boat does have a depth finder installed but I would honestly be shocked if it was integrated into the factory warning system.

As far as damaging a wiring harness, there wasn't anything I did that felt or looked sketchy. I'd think with a short in a wire there would be some correlation between movements of the boat and the noise, where this has happened dead still on the trailor.

 

[bradiggy]

The audio warning system mentioned has a built in test for proper operation. With the key in the run position engine not running it should sound constant or at least for a few seconds depending on engine model. Key on, engine off the alarm sounds from a lack of oil pressure, easy test.

If the oil pressure switch can trigger an alarm without the engine running, would you be inclined to replace that first just to get that off the list of possibilities?

 

[dubs283]

If the oil pressure switch can trigger an alarm without the engine running, would you be inclined to replace that first just to get that off the list of possibilities?

No

Based on the info provided I'd be suspect of a short somewhere, possibly a faulty key switch. Might also be a chafed wire(s) at/near the helm

 

[dubs283]

Thinking more on it'd be best to disconnect the oil pressure switch and see if the problem goes away/continues

 

[Fun Times]

Found serial number tag; L653238. Can ya'll confirm exact engine name so I don't look dumb in the future!

0L653238 has the engine to be a MERCRUISER 5.0L ALPHA
Sterndrive Models GEN+ (LH rotation), roller lifters, 2-bbl intake, Model number 4M11025LS.

Here's your engine parts guide, https://www.mercruiserparts.com/5-0l-2-bbl-gm-305-v-8-1998-2001-0l0

Agreed with Dubs with disconnecting the oil switch and then also try the 2 wires on the gear oil reservoir and then the temp sending unit at the thermostat housing with two wires yellow and black... If that/one of those don't stop the warning horn, let us know as there will be about two other things to try/test.

 

[bradiggy]

Got parts in for the impeller, so I cracked open the lower for the first time. I'm wondering if this is bad enough to cause low pressure / high temp and trigger an alarm. It doesn't really ad up given the conditions that alarm triggers. Regardless it needed to be replaced. Also should have a new thermostat before Saturday.

I'll hit the lake on Saturday and will mess around with the sensor switch wires some more - expect a report on Sunday!

(I'm guessing this is about as close as it gets before it starts losing big chunks into the cooling system)

 

[Fun Times]

^
Yeah , that could be an issue.

Probably time for a full service for the entire engine and drive components.

 

[alldodge]

^
Yeah , that could be an issue.

Nah that will have no effect

 

[bradiggy]

^
Yeah , that could be an issue.

Probably time for a full service for the entire engine and drive components.

What more needs to be done after oil change, filter, fuel filter, new thermostat, new impeller, and gear lube change? There surely can't be too much more I was thinking upper drive / bellows at the end of the summer since I'm not having any water intrusion issues.

 

[dubs283]

Can't recall ever seeing a gen 2 impeller that cooked before.

Based on your previous posted temps with an IR temp sensor that is testament to Mercury's upgrade from the alpha one style pump

 

[bradiggy]

Can't recall ever seeing a gen 2 impeller that cooked before.

Based on your previous posted temps with an IR temp sensor that is testament to Mercury's upgrade from the alpha one style pump

I had the IR gun on board last Saturday and after a WOT run the starboard riser showed 165, 140 on the port. I figured the impeller wouldn't be THAT bad if I wasn't even clearing 175 degrees. (I also thought they were known to break apart rather than the more 'melted' look of this one). I'm glad I caught that before summer really gets going.