Battery Master Switch
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Joined: Jan 2010
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Battery Master Switch
I installed a master switch on the ground cable from the battery on my 1986 Coupe.
When I switch on the battery after the car has sat for a week or so and start it up, it doesn't run very well at first.
Is this because the ECM loses its settings when I shut off the power to the computer (ECM)?
If so has anyone tried one of those 9 volt batteries that plug into the cigarette lighter to keep the ECM energized?
Does that solve the problem?
How long does the 9 volt battery last when powering the ECM to keep its memory?
Is there any issue with shutting down the ECM repeatedly that I could cause damage to it?
Thanks for the information
When I switch on the battery after the car has sat for a week or so and start it up, it doesn't run very well at first.
Is this because the ECM loses its settings when I shut off the power to the computer (ECM)?
If so has anyone tried one of those 9 volt batteries that plug into the cigarette lighter to keep the ECM energized?
Does that solve the problem?
How long does the 9 volt battery last when powering the ECM to keep its memory?
Is there any issue with shutting down the ECM repeatedly that I could cause damage to it?
Thanks for the information
Tech Contributor
Joined: Oct 2008
Posts: 3,729
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From: Custer, WI
I'm not sure that you could damage the ECM by resetting it 1000 times,
but I do believe that the reason it runs rough at first because it has to relearn everything.
No idea on the cigarette lighter.
but I do believe that the reason it runs rough at first because it has to relearn everything.
No idea on the cigarette lighter.
Team Owner
Joined: Sep 2003
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
The kill switch is a great idea.
But, there is no advantage to leaving the system off unless you have a drain on the battery that needs to be fixed anyway.
IMO add a Battery Tender to your garage to keep the battery topped when not in use.
And yes the car is running like crap because the ECM stores "learned" info for the next start.
But, there is no advantage to leaving the system off unless you have a drain on the battery that needs to be fixed anyway.
IMO add a Battery Tender to your garage to keep the battery topped when not in use.
And yes the car is running like crap because the ECM stores "learned" info for the next start.
Last edited by JrRifleCoach; Aug 4, 2011 at 12:11 AM.
Thread Starter
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Joined: Jan 2010
Posts: 73
Likes: 0
The kill switch is a great idea.
But, there is no advantage to leaving the system off unless you have a drain on the battery that needs to be fixed anyway.
IMO add a Battery Tender to your garage to keep the battery topped when not in use.
And yes the car is running like crap because the ECM stores "learned" info for the next start.
But, there is no advantage to leaving the system off unless you have a drain on the battery that needs to be fixed anyway.
IMO add a Battery Tender to your garage to keep the battery topped when not in use.
And yes the car is running like crap because the ECM stores "learned" info for the next start.
Sounds as though I can keep switching it off without doing damage to the ECM.
I think it to be a worthwhile effort to try to track down the draw.....something to do in my spare time.
Thanks guys
Race Director
Joined: Apr 2003
Posts: 17,697
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From: moraga ca
Hook up an ammeter between the positive cable and the battery. Check the reading and note the current draw. Pull the fuses one by one untill the draw decreases significantly. You have now found your drain.
