Mercuiser engine on Sea Ray 280

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Stephen W

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Warning light came on saying "Sensor power supply voltage is low - non critical.
Engine wouldn't start although battery seemed ok i.e. starter turning over but wouldn't start.
Battery man looked at battery and connection was loose. He repaired and tested and all good.
Warning message still showing however even though battery showing 14 v.
Went out again and engine restarted twice out at sea but didn't start in lock on the way back.
Same message showing - battery reading showing 12.5 v and 61.5 hours.
Battery man said this was normal and engine should have started.
Can anyone help?
Does the system fault need resetting - I have reset on boat but system fault message still showing
Thanks
Stephen W
Engine model is : Mercruiser 8.2 Mag 380hp V8
 
Last edited:
Hi there.
I have a feeling this is an mpi, is it ? If it is I know what the issue is. I’ll wait for you to get back before I drone on. It’s long winded to explain
 
The sensors on the engine work on 5v, so a low voltage here would give incorrect readings from the various sensors, which will give start and running problems. The 5v comes from the ECU and goes to different sensors on the engine, so I would start by checking the main plugs on the ECU. First to see if you have 12v going in and then 5v coming out. Also check the main engine earth and ECU earth.
 
Stephen W said:
Yes it is an mpi
Click to expand...

Ok. So there is a good chance it’s the following.
A few years ago I tried to start my mpi after a long winter. I hadn’t charged the battery for a couple of months but chanced it anyway.
Upon trying to start it, it would seemingly turn over very healthily, but not fire, but occasionally give a wee kick as I let go of the key.
Happened a few times and had done since every other year since. It was always the battery. The smart craft showed a low voltage error each time.
Eventually I figured it out after initially dismissing the battery as good (because it turns over fine). It was in fact the battery.
It turns out that these MPI are that power dependant during start up that anything other than a tip top battery wont fire her.
What happens is that the load taken by the starter reduces the power to the ancillary systems (ecu and 5v system) that it won’t get a signal to fire....that is, until you let go of true key and for a split second the power demand from the starter releases and for a brief second the engine tries to fire on occasion.
This may not be your issue, but it’s worth a try and defo a know known issue with the MPI engine.
Other than that, you need to check for 5v at all plugs and control systems.
The well know crap cap (diz cap) failing could also be an issue. These sometimes short to the casing with dampness. They are well known to fail frequently. I’ve been through 5 in 5 years.
The SW pressure sensor is another known weak point. The sensor fails and messes up the whole 5v system.
Try these and see how it goes. Honestly. I’ve had just about every common issue there is with these. Managed to get a hold on it now though. Great engines once you are in the know.
 
Thanks. Sorry I’ve taken so long to respond however have been away.
I will look at all your points and let you know how we get on
 
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