Mercury 6.2 ECT DTS Axius Voltage Issue

[tpenfield]

. . . the hits just keep on coming . . .

I've been doing a bunch of work on my boat and engines . . . mostly of the electrical nature.

Anyway, I am getting low voltage warnings on the starboard engine. Once the engine starts the warning goes away and the VesselVeiw says "OK".

I then noticed that when I turn the engine battery switch off, the master relay starts buzzing (engine off of course). If I turn the the battery switch back on - the buzzing stops.

.

I swapped out the relay and it made no difference. (The new one buzzes too)

To hopefully see more info, I hooked up my Diacom and recorded some data.

First is the starboard engine:

Not running


Running

.
Here is the Port engine, which looks fine
Not running


Running


I believe the voltage titles in the Diacom might be incorrect and should be swapped. Anyway the key symptoms are low system voltage on Starboard engine prior to starting, and more normal voltage while running, then buzzing of the relay when the battery switch is turned off.

Port engine looks/acts fine.

I am just wondering what is dragging down the voltage on the starboard engine while it is off. Here is the summary of what I have found . . .


Recent work done on starboard engine/electrical ( I know it is always the last thing you did/touched ) (maybe)
- New alternator
- Cleaned up a few of the power connections on the starboard positive isolation post.

This one might be something for @Fun Times and @muc to take a look at . . .

T.I.A as always.

 

[alldodge]

Check were your keep alive connection is, it should be directly on the Bat post

Maybe measure your Bat to see if if agrees with Diacom. If it does might be time for new Bat(s)

 

[tpenfield]

Thanks, AD . . . There were a bunch of wires connected to the starboard isolation post . . . one of them was a bit 'sparky' when I re-connected it after cleaning the connections.

I'll get the DVM and start poking around, both with ignition off and on.

I'm coming in close behind you on not loving these hi-tech boats. Still saving my allowance to buy something else.

 

[tpenfield]

BTW - I pulled and re-connected all of the connectors on the PCM 112, the Smartcraft junction box at the helm, and another PCM looking thingy at the helm. No difference.

 

[nola mike]

I'm coming in close behind you on not loving these hi-tech boats. Still saving my allowance to buy something else.

Make me an offer. Very low tech. Running well enough that I cleaned non-essential connections last weekend (radio, after guests argued that it was, in fact essential).

 

[nola mike]

1. Didn't you have a similar issue when you bought the boat?
2. Where are battery voltage/system voltage measured?
3. Do you have a wiring schematic for your boat? At least a low level how the batteries are connected, battery switches, house batts, etc?
4. Did you measure voltages yourself at battery, alt, PCM, relays, and diacom connection port?

That buzzing relay sounds like it isn't getting enough volts to hold it closed, but shouldn't be getting anything with batt switch off. So a low level short to power somewhere maybe. Does it buzz with key off/batt switch on? <--EDIT, saw the answer to this. Did you check relay volts in both cases?
How about key on/switch off?

 

[Fun Times]

At the moment I may have yours confused with alldodge...Were the batteries just ordered and installed new?...Plus wasn't recently an issue found with the battery switch and a new one put in? Or was that AD?

The thicker wiring color coming of the back of the alternator, is it Orange or Red? Or?

The reason for the new alternator at 6 hours was?

How many wires are running to the back side of the battery switch? On both engines that is if you have 2 switches or 1?

Even 11.4v is a tad low too but 9.4v would make a relay do that where 11.4 may not but need to figure out why you're still getting power past the battery switch to still power up that side of the engine vs say a bilge pump switch, etc. if it's designed that way on your boat model.

 

[tpenfield]

1. Didn't you have a similar issue when you bought the boat?
2. Where are battery voltage/system voltage measured?
3. Do you have a wiring schematic for your boat? At least a low level how the batteries are connected, battery switches, house batts, etc?
4. Did you measure voltages yourself at battery, alt, PCM, relays, and diacom connection port?

That buzzing relay sounds like it isn't getting enough volts to hold it closed, but shouldn't be getting anything with batt switch off. So a low level short to power somewhere maybe. Does it buzz with key off/batt switch on? <--EDIT, saw the answer to this. Did you check relay volts in both cases?
How about key on/switch off?

#1 - Yes, voltage warning on the starboard engine . . . sort of got it fixed after a while.

#2 All over the place. Everything VesselView and Diacom are coming from the PCM. I have taken other readings with my DVM. The voltages are there, it is just that the PCM isn't seeing some of them properly.

#3 Yes, boat and engines. Not a quick read though . . .

#4 - It is hard to get voltages at the connector pins . . . very little wiring exposed, much of it is terminated at connectors.

I'd have to get special connectors to be able to probe the leads. Not sure there is even such a thing . . .

The engine is definitely getting battery power, based on my DVM probing, both ignition off and ignition on. I think it is the PCM that is not getting a proper signal. There are 3 pins in question of the controller connectors that would be a voltage source.

My thought right now is that there may be a voltage loss at the Axius clean power CB's. It looks like one of them already got replaced, but it does not appear to be a quality component.

I'm going to order a couple of Circuit Breakers and see where that leaves things. Fingers crossed. . .

 

[alldodge]

Another thought, might be the 4th beer but oh well

There should be no power on any of the relays. When key is turned ON it powers the MPR which turns everything else ON. Wonder if it's something like the MPR is staying slightly energized.

 

[tpenfield]

At the moment I may have yours confused with alldodge...Were the batteries just ordered and installed new?...Plus wasn't recently an issue found with the battery switch and a new one put in? Or was that AD?

The thicker wiring color coming of the back of the alternator, is it Orange or Red? Or?

The reason for the new alternator at 6 hours was?

How many wires are running to the back side of the battery switch? On both engines that is if you have 2 switches or 1?

Even 11.4v is a tad low too but 9.4v would make a relay do that where 11.4 may not but need to figure out why you're still getting power past the battery switch to still power up that side of the engine vs say a bilge pump switch, etc. if it's designed that way on your boat model.

My boat has 340 hours.

Starter batteries (2) are new.

The Starboard alternator stopped charging properly when I test ran the engines this year. It was replaced a few days ago as per my write-up.

Each engine has its own battery & switch. It is a Mercruiser 'faux pas' to run the engines on a single battery source. The starboard engine has the crown jewels in terms of running the DTS & Axius.

There are more wires than I can count on the back side of the battery switch. I'll take a closer look in the day or 2.

I'm thinking it might be a 'clean power' issue. So, I'll replace the CB's

 

[tpenfield]

Another thought, might be the 4th beer but oh well

There should be no power on any of the relays. When key is turned ON it powers the MPR which turns everything else ON. Wonder if it's something like the MPR is staying slightly energized.

Here is the area of the wiring diagram for the MPR.

.
The power feeds end up over on the other side of the diagram at the connectors to the PCM.

.
Based on the PCM Manaual, I beleive that power is on connector A (58) pin A2 and Connector 3 (56) Pin A4.

Here is the detail from the PCM 112 manual. I believe the relay shown is the MPR


.
Here are a couple more power feeds. There is a fuse holder on the engine that has the 2 amp and the 20 amp fuse. (both check good . . . all of the engine fuses looked good.


Here is the entire schematic from the Mercruiser Manual.

.
Looks simple, right?

 

[alldodge]

Another thought (now it's wine)
This all started after cleaning the other side of the boat electrical area, right?

 

[tpenfield]

Another thought (now it's wine)
This all started after cleaning the other side of the boat electrical area, right?

No I cleaned the starboard side. I did quite a few things in short order, so it is hard to say what may be contributing to it.

• Battery upgrade
• New Alternator
• Cleaning Electrical box

 

[tpenfield]

Another thing that I just thought of is that there are quite a few circuit breakers up at the helm under the instrument cluster. I should check those to see if there is anything of significance.

 

[nola mike]

My question was in the diacom, where is "battery volts" being measured at vs. "system voltage".
I think the first thing I would do is measure the voltage at the relay when it's clicking--I bet you're getting that 9v there. If so, disconnect the wires from the battery switch. Something is presumably back feeding the switch; find out which wire still has voltage to it. That should help you narrow down the circuit. Also, if you can't back probe the connectors, get some insulation piercing DVM leads. (and meanwhile, back in 1992...)

 

[Fun Times]

One thought that comes to mind to consider trying as well would be while the relay is buzzing, start pulling one fuse at a time all over the engine to see if maybe one of them is back feeding but pull the Main relay fuse last if possible.

Also is this happening when the boat's other house power is powered up too?

Maybe it's a bad diode someplace.

Maybe another test to prepare for would be makeshifting an 14 pin ignition key remote switch such as something like this,
https://www.mercruiserparts.com/15000a14-remote-key-switch

^ Which would help tell you if you need to be working on the engine side or the boat side of the power system. Separating the boat from the engine is often a good diagnostic tool.. Yours being newer is just a bit more challenging but I think I have a couple of ideas to explore if time goes by and you're still not sure what's going on.

Again: The thicker wiring color coming of the back of the alternator, is it Orange or Red? Or?

 

[Scott Danforth]

I'm coming in close behind you on not loving these hi-tech boats.

Teds Luddite build coming next.....

 

[tpenfield]

@Fun Times I am not sure of the wire color on the back of the alternator, but the protective boot is orange. (sorry for the delay in response)

 

[Fun Times]

@Fun Times I am not sure of the wire color on the back of the alternator, but the protective boot is orange. (sorry for the delay in response)

No problem, next time you're in there try to take a peek.
I'm thinking if the wire is orange then it's a stock set up and running down by/to the engine starter...If red then usually something aftermarket with an isolator of some sorts mounted elsewhere....Try to follow the wire just so you know what's going on and if it could be a potential issue on top of anything else.

 

[Lou C]