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Does fitting an isolator switch cause EMC to loose it's memory

N

nimbus

Member
A few weeks ago whilst the pontoon was being completed, the boat was unused for a couple of weeks and the internal lights were left on, result: a very flat battery which I was fortunate in recovering by a slow recharge.
On this boat a 'Monterey', all the electrics seem to be left on when the ignition key is removed, including all auxiliaries. So I installed an isolator switch, problem solved.

Except that I have been reading the Penta service and repair manual, and under the subheading "Fuel and Ignition Systems' I was surprised to read this:----

"The EMC has a 'learning' capabillity. That is, if the battery is disconnected for any reason, the learning process has to begin all over again"

I have checked with the Volvo people who are trying to assertain if the above is correct

The 'learning process' would be relavent to the ECM adapting to the condition of the engine, fuel grade, ect. And surely
you would not want this data to be erased after every trip when you turn off the Battery Isolator switch.
 
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There is a second smaller size wire attached to the battery, I reasoned that this was the common 12V supply to all equipment.
The large cable of course goes to the starter.
The schematics supplied with the boat are not very imformative and very unclear to say the least about them!!. So I am now studying the mass of schematics in the manual.
However,. disconnecting the battery should be normal practice before doing any work on a boat, changing oil and fuel filters, oil changes, coolent changes ect. So every time this occurs the stored data is lost????
On a car radio it is implemented on purpose as an anti theft feature.
I have just located the pertinant schematic for my engine, and sure enough it shows the 'Battery Switch" (optional) totally disconnecting all 12V power to the engine systems.
 
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nimbus said:
............ I have just located the pertinant schematic for my engine, and sure enough it shows the 'Battery Switch" (optional) totally disconnecting all 12V power to the engine systems.
Click to expand...
Most good marine wiring that includes an MBSS (main battery selector switch) does allow for complete interruption of 12 vdc when the MBSS is turned OFF.
If Kim is correct, and if the ECM requires continuous and uninterrupted power, you can take this from the #1 terminal of your MBSS.
(#1 should be your cranking battery bank)

This is schematically the same as a direct battery connection, but it eliminates the potential Rat's Nest and small terminal corrosion that we see at our battery banks.
It also becomes a more permanent connection, and lessons the likelihood of a mistake when doing battery R&R.


.
 
What you are referring to is usually termed the KAM - Keep Alive Memory and really isn't an issue as there really isn't much "feedback" for the ECM to "learn from"....what it can learn will be done so very quickly so there's not much benefit to loose. The big factor is in where you located the isolator switch, electrically, with regard to the battery and the ECM....
 
Hi makomark,
The isolator switch is mounted on the bulkhead almost on top of the battery. it is a proper flame/vapour proof marine switch rated at 400A. This allowed me to use the existing lead from the starter/alternator to the switched terminal and using just a short standard lead to the common from the battery +.

I have also wired-in direct to the battery terminals, a 24+7 trickle charger; designed in Sweden which on paper seems to be a clever device. This unit has a reverse discharge rated in micro-amps. and is a pulse type.

The more I think about this the more I am thinking that the statement in the manual is wrong.
"The ECM has a 'learning' capabillity. That is, if the battery is disconnected for any reason, the learning process has to begin all over again"
Because surely the stored "fault conditions" would use the same memory type.
 
If its a newer GM block and ECU, the "faults" are stored in a different memory....without the O2 sensors, the ECU has limited feedback from which to learn, especially when it comes to fuel trim...the other stuff is quickly "relearned"...I'd say give it a whirl and see how it goes, especially if you know it will mitigate the dead battery syndrome...
 
Yea, I've been using the isolator setup for the last three weeks with no decernable problems, so I will just forget about any loss of learning!!
 
Nimbus, FYI......

This is a battery "isolator".
80050TH.gif


This is a BS... Battery Switch.

images


This is an MBSS..... main battery selector switch... Off/1/BOTH/2.

images
 
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