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Old 01-05-2016, 06:01 AM   #1
Ocean Blue 2.7 2000MY 986
 
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1st Boxster, 1st Problems

Hi Guys
I have just bought my wife a Boxster for X-Mas to replace her beloved MGF
The first day home the alarm went off and we found that the battery was completely flat. 1st problem was how to release the front lid - a quick google search pointed to supplying +12v to fuse C3 which we duly did, opened the lid and replaced the battery with a new Silver 85Ah 850CCA model. All was OK for another two days until the same thing happened
Monitoring the static drain on the battery shows a very strange pattern. Normal background drain is about 50mA but this spikes to 6A, 8A or even 10A for about ten seconds every minute then it drops back down to the normal 50mA
Systematically removing the fuses whilst monitoring the batter drain led us to fuse E3 (30A) which would appear to be related to the Power Seat Memory which is doubly odd as the car only has manual seats!
I have a workshop manual on order to help me with further diagnosis but until this arrives does any of you tech savvy guys have any idea what could be occurring ?
Cheers
Stuart
Ludlow UK
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Old 01-05-2016, 06:42 AM   #2
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This may be a long shot. Do you have any water/dampness under your seats?
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Old 01-05-2016, 06:47 AM   #3
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ditto - the power seat plugs are still in the harness, even if you don't have power seats. they sit under the seats. if it is wet under there something might be shorting out. or a wire might be worn though and shorting to ground (harder to find). if the power seats are the only thing on the circuit perhaps just leave the fuse pulled in the interim?
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Old 01-05-2016, 10:34 AM   #4
Ocean Blue 2.7 2000MY 986
 
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Fuse E3 drain

Hi Guys
Thanks for your replies
The car is bone dry everywhere.
I find it odd that the current drain is cyclical and in bursts of about 10 seconds then nothing for about a minute. If it was just an earth leak, shorting cable, damp harness etc I don't think you would get this type of behaviour.
It is too regular and is repeatable
Does anyone know what else is on the fuse E3 circuit?
Cheers
Stuart
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Old 01-05-2016, 11:02 AM   #5
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What year? I'll check the wiring diagram.

Edit: as TRK stated, the only devices on E3 are the left side seat memory and backrest tilt.

Last edited by particlewave; 01-05-2016 at 11:16 AM.
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Old 01-05-2016, 11:02 AM   #6
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e3 is left seat memory and backrest control only. note that all the seat functions go through the ecu, so it may have some logic that is pulsing it like that (ie, shorted wire or connector is sending an activation signal, and ecu is trying to comply but not getting results so cycling).

I have a copy of the applicable schematics but it's a 22 MB pdf. you used to be able to download from cannell.co.uk but site is down.
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Old 01-05-2016, 02:35 PM   #7
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On a used Miata I bought in the past, I had the same behavior. Consistent dark current jump to 1A or so every 10 seconds which caused the battery to die after ~a week.

Took me awhile to find it but turns out there was some gimmick device installed meant to pulse the body of the car with 'negative ions' to keep rust from forming. I found the device on the inside of the firewall, with two electrodes touching the bare inner fender. About 5 seconds later, my dark current drain was gone.

I forgot the name of the manufacture but once I looked it up, they had many lawsuits against them for false advertisement and had since gone out of business.
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Old 01-05-2016, 02:45 PM   #8
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dude - I spend a summer in university working on that - called 'cathodic protection'. you introduce a current that offsets the electron flow cause by corrosion. used it to try and prevent the corrosion of steel in bridge decks.
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Old 01-06-2016, 09:24 AM   #9
Ocean Blue 2.7 2000MY 986
 
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The car is in lovely original condition - as far as I can tell! It seams watertight and nice and dry
It has manual full grey leather seats without the heating option.
Fuses E3 & E4 are both 30A and should be for seat positioning/memory so are not in use on this car
As a temporary fix I have removed E3 and the dark current has dissapeared and everything seams to be working fine. No warning lights or ecu/canbus errors

I'm not happy to leave it like this until I have found the actual cause so any further help would be appreciated

Regards
Stuart
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