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PostPosted: July 22, 2016, 10:46 am 
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Joined: October 13, 2011, 9:19 am
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Location: Denver Co
Yeah i am trying to find out how you find a drain on the car. Pretty much every time I shut the car down i have to flip the kill switch too otherwise the battery will drain. This usually isnt an issue but it wipes the short term fuel trim on my computer.

any help?

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PostPosted: July 22, 2016, 11:10 am 
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Clamp on amp-meter. Start at the fuse block and test each branch.

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PostPosted: July 22, 2016, 11:11 am 
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Pull the + connection of the battery, bridge the gap with an amp meter, you should have 0 amp draw. If you have a draw start pulling fuses until it goes to 0, they at least you will have a area to start looking.


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PostPosted: July 22, 2016, 11:21 am 
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^This.

Keep in mind that all ECUs do pull some amount of standby power. If the battery is small and/or weak, given enough time it'll drag it down. By habit, any time I know the car won't be driving for a week or more, I connect the battery tender.

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PostPosted: July 22, 2016, 11:27 am 
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oldejack wrote:
Clamp on amp-meter. Start at the fuse block and test each branch.

Can clamp-on meters measure DC current? I looked briefly online and they get a little squishy on that. I think for DC current you may have to wire it in like normal.

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PostPosted: July 22, 2016, 11:33 am 
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KB58 wrote:
oldejack wrote:
Clamp on amp-meter. Start at the fuse block and test each branch.

Can clamp-on meters measure DC current? I looked briefly online and they get a little squishy on that. I think for DC current you may have to wire it in like normal.

There are DC clamp on meters, but they're usually quite a bit more money than just a cheap AC only one.
Kristian

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PostPosted: July 22, 2016, 3:04 pm 
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Yep. I use a clamp-on ammeter for all my parasitic-draw testing so that I don't have to disconnect customers batteries. I have had once or twice where it read inaccurate though.

Assuming you only have a multi-meter:
-disconnect battery and let sit for 1min
-touch disconnected cable back to battery and see how big of a spark. If a large spark, use a test light for testing so you don't blow your meter's fuse. Otherwise connect your meter (set to DC amps) to the battery post and the disconnected cable. Let it sit for 1min while the capacitors etc fill up. With an ECU, your draw should be less than 50mA. If it is more, start disconnecting fuses one at a time until you see the draw drop down to under 50mA. Then once you know what circuit is drawing, try to isolate further by disconnecting components on that circuit. BTW, most of the time it will be aftermarket components that are the problem.

I'm sure Youtube has videos to demonstrate and help you search for "parasitic draw".

Cheers.

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PostPosted: July 22, 2016, 11:43 pm 
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Or you could just connect a 12 volt light bulb between the removed positive battery cable and the positive post. If you have current going out, it will light the bulb. Like said above, remove one fuse at a time while watching the bulb. If it dims a little, you've found one of the drains. If it goes out you found the only drain. Start with the smallest bulb you can find or use a 12v LED. Arranged in the right direction of course, it is a diode after all and will only pass current in one direction.

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