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ls swap parasitic battery drain

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Old 05-15-2018, 10:02 PM   #1  
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ls swap parasitic battery drain

I may be making this into a larger issue than it is but it seems like if i leave my car sitting for 2 weeks or so the battery is very noticeably drained. I realize leaving it sit for that long its bound to happen but i don't ever remember it being quite that fast. I've got an 84 firebird that I've swapped an ls3 into. Everything seems to be working fine. I ran through the procedure to track down parasitic loss. I came up with 34 mA. I think anything under 100 is not supposed to be too bad, but the fuses i found the draw on aren't what i expected.

7mA from Courtesy fuse
2mA from stop/hazard fuse
24 mA from fuse 11 in the GMPP LS fuse block labeled Bulkhead cont. Power

The meter always reads 34 mA to start with then very slowly starts going down about .1 mA every few seconds. I left it connected for a few minutes but it only went down a little past 33 mA, the decrease seems to be on the new fuse box side.

looking at the wiring diagrams seems like the stop/hazzard is probably the radio. And all i can tell on fuse 11 is that in the LS swap guide its also called Cigar accessory and ties into the Data Connector. Doesn't seem like anything except the radio should draw power. I could understand if it was the ECM fuse but I've no clue what might be sucking the power.

I don't think that my cigarette lighter even works in my vehicle so other than it and the dome light i don't know what is on the courtesy fuse. I had previously had issues with the driver side door switch not functioning till i sprayed electronics spray into it and pulled and twisted on it some to hopefully clean the connections. It works now and doesn't seem like its an issue

Anyone have any ideas what i could try checking at the source or unplugging?
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Old 05-15-2018, 11:38 PM   #2  
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Re: ls swap parasitic battery drain

34mA isn't bad at all.

The courtesy fuse is hot at all times and is for interior lighting.
cigar lighter
glove box light
dome light and floor lights (grounded by door jam switches)
dome light and floor lights (operated by dash light switch)
cargo compartment light
There might be something else on that circuit.
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Old 05-16-2018, 05:39 AM   #3  
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Re: ls swap parasitic battery drain

The radio isn't on the stop/hazard circuit. It IS however on the "courtesy light" circuit: that's its source of constant battery that holds up the clock and the pushbutton memory. It MAY ALSO be the source for anything aftermarket that's been installed; amplifiers, alarms, remote starts, etc.

I doubt messing with the door switch would change anything in regard to a "parasitic drain". Any dirt or other schmutz on it isn't likely to conduct enough current to be significant. Not saying that you shouldn't have done that, or that your contacts were fine, or ANYTHING like that; only, that doing that, is vanishingly unlikely to have had any impact on the matter at hand. Likewise, the cig lighter itself would have to have some pretty groaty funk built up on it, which would probably be staying warm enough to smell 100% of the time, if it could conduct current constantly. Also not likely to be a factor here.

24 mA on the batt line to the ECM sounds pretty much in line with normal reality. I suspect that just about any modern car won't last more than a few weeks of sitting without draining the batt.

I'd suggest one of those solar "battery tenders" like they sell for boats... doesn't take much juice obviously, doesn't have to be a real hoss or anything. If you put one on it that can deliver 100 mA, that would be enough to supply the "drain", as well as the battery's own natural internal "drain", during the 50%ish of the time that there's sunlight to work it.
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Old 05-16-2018, 06:18 PM   #4  
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Re: ls swap parasitic battery drain

I'd be inclined to agree on the ECM the only issue i have with that is there are 2 fuse 1 labeled for the ECM and another for ECM keep alive but neither of those are the ones drawing the power. I have an after market radio but its just a cheap replacement unit no extra amps. I think the wiring was spliced in for that but it wasn't something I did so i don't know if the pulled power from somewhere strange. The wiring diagram i saw showed the radio alarm running off the stop/hazard so that's why i figured that was the radio. Its possible that they both are in one way or another or that it didn't have a factory alarm so that circuit should be dead. I was going to attempt to unplug the controller for the transmission and see if that is what is pulling the 24 mA otherwise i'm left with taking the fuse out and seeing if any trouble codes pop up or if i notice anything without power.

Probably not worth tearing the car apart to figure out.
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Old 05-17-2018, 11:44 PM   #5  
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Re: ls swap parasitic battery drain

I found the root of the 24mA draw. It is the Transmission control module. Can't really do anything about it and not sure why it doesn't have an efficient sleep mode like the ECM. I'm assuming the rest is the radio.

If i can figure it out i may look into switching the fuse to a circuit from a switched source.
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