Warning horn - merc 5.0 efi with alpha

[chortle]

Hi all

Hoping someone experienced with these can help with a problem that I experienced while out yesterday. The horn sounded about an hour out (including about 15 mins at c 3200 rpm). Before that running at hull speed or below (coming out of Lymington river).

I came down to idle and the horn stopped. All gauges reading fine - temperature 170 (normal for me) and oil psi around 40. Turned off the engine and checked the fluids. Gear lube and oil looked fine. Dry and clean bilge. Returned to the yard keeping it under 2000 as much as possible (but had to run a little faster through Hurst).

intermittent horn at all rpms (every 5 mins say) sometime with a slight loss of power (cleared by going to idle). Idling smooth - no weird noises. Occasional pressure fluctuation on guaage but never below 30 at 2000rpm and usually at 40. A couple of time fell a little lower when dropped to idle (or just over) - maybe 20-25.

temperature never moved. The boat has has a full service over winter by local mercruiser dealer and this was third trip out since It’s a mefi 1/2 engine (throttle body) with about 350 hrs.

I am thinking maybe a faulty oil pressure switch or a bad ground. Or maybe a battery issue. Obviously worried there was a real oil pressure problem. Not sure if there is a third sensor for that (other than guage sender amd the switch).

anyway can’t get anyone to look at it until tomorrow and was hoping someone smarter might recognise the symptoms. I didgo back today and dipped engine oil now it is cold. Not overfilled - looks fine. Gear lube also to the top line. The gear oil is Green tinged - quite thin. I thought it would be thicker. But maybe just because it is new. I will get that checked but in any event the bottle reservoir is full.

The only thing done prior to this run was by an electrical engineer to reconnect the port battery to the voltmeter and fix a mistake with a new audio unit that was wired in (permanent memory lead to bypass switch).

I don’t have a scanner tool or anything like that. But hopefully they can do that tomorrow. But any thought welcome. It seems strange that the horn self cleared like that. I suspect the oil pressure switch because i felt a momentary drop in power. I think this might have been the ecm turning off the fuel pump or similar. But the guage never went anywhere near the switch pai threshold (which I believe to be c 5 psi).

best

eddie

 

[Mr Googler]

Here’s the beeps list

https://media.channelblade.com/EProWebsiteMedia/3506/Mercruiser warning horns.pdf

 

[spannerman]

Sounds like it could be the seawater pump pressure sensor if you have one fitted. At the back of the engine there should be an oil cooler for the servo steering, look to see if its got a brass coloured sensor on top at one end, I have changed a lot of these as they get salt crystals in them and then don’t work correctly, if you have Smartcraft instruments you can display sea water pressure, it may not have been selected but its in the list of parameters that can be selected for display. It will give power reduction if the pressure is low, alternatively your engineer will be able to read it on the Mercruiser test programme.

 

[chortle]

I don’t think it has one. It’s an early efi looking at the horn warnings - it’s only water temp, oil pressure switch or gear lube float switch. Or a bad electrical connection/ground I guess.

 

[QBhoy]

Sounds like it could be the seawater pump pressure sensor if you have one fitted. At the back of the engine there should be an oil cooler for the servo steering, look to see if its got a brass coloured sensor on top at one end, I have changed a lot of these as they get salt crystals in them and then don’t work correctly, if you have Smartcraft instruments you can display sea water pressure, it may not have been selected but its in the list of parameters that can be selected for display. It will give power reduction if the pressure is low, alternatively your engineer will be able to read it on the Mercruiser test programme.

Smart craft won’t be compatible with an efi mercruiser spanner man. Too old. These are just basic throttle body injection things.
So very few things can alarm on these efi. Gear lube header tank float sticking or sinking being porous is one of them. Another is an IAC (if your year has one. Think it’s has. Or high temperature. I’d just maybe be having a thought around the latter. 170 is getting up there for temperature perhaps and with dash gauges famously being known to read up to 20 units out either way...I wouldn’t totally trust it. You should have a 160 thermostat if she is raw water cooled like most of them. 140 if she has fresh water cooling. I’d have a look at the water pump perhaps.

 

[jrudge]

I know nothing about these engines but an alarm that stops when you reduce power points to temperature.

Volvo have a temp sensor and also a separate alarm sensor. No idea Re your engine but if you have 2 the alarm sensor could be faulty -or of course it is actually over heating !

 

[B58]

Please check the water inlet on the back of the transom remove the pipe and make sure the water hose hasn't collapsed? If clear check the water pump for wear, the alarm will come on if its overheating through loss of flow, while underway when the alarm comes on, check to see if the temp gauge fluctuates?

 

[chortle]

Hi all. Thanks for all of this advice. I took it out with an engineer who had the (ancient) ecm scanner attached as we ran. Replicated the issue with no codes showing. In the end I realised that the batteries weren’t charging underway (the gauge looked ok but it was clear from my separate digital voltmeter). The ecm must have been tripping momentarily due to under voltage as the batteries started to run toward and below 12v.
New alternator fitted and no more warning horns!