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Discussion Starter #1 (Edited)
When I installed my audio system 3 years ago I also upgraded the main power and grounds under the hood.
Alt+ to Batt+
Batt- to drivers strut tower. This really should be protected with a fuse but the thick casing on welding cable, wrapped in split loom tubing and being inside of the factory plastic routing guide, I think it would take a catastrophic accident to short it to ground. I'll risk it.
Strut tower to top of transmission
That is what is sometimes referred to as "the big 3 upgrade".
The headlights do not dim when audio is pushed. Good, Objective completed I thought, but the dash lights would still dim. Also if I pushed the audio to insane levels at idle the engine would run rough.
I noticed much later that I had overlooked another, smaller ground from the passenger top of transmission to firewall. It is Black/RedStripe 12-14G? I've been meaning to do that one for a while. It couldn't hurt I thought. I still had some welders cable and lugs.
I added an upgraded ground there and something unexpected happened. When adding the new trans to firewall ground there was a small spark, even while the prior grounds were still attached. I brushed it off and didn't think too much about how that shouldn't have happened. After the ground was secured and the car started, The factory stereo turned on by itself. (I have 2 stereos hooked up, I haven't turned the factory system on in years). I thought of that unexpected spark again. The dash lights are now brighter, notably the orange airbag/trip computer gizmo.
After driving for a couple days I've noticed a change in driveability. The shifts are a bit sharper and has less of the lag it had before. I've experienced this before as a computer learns your habits after a reset event. The difference seems to be that it has stayed this way after several days, a bit peppier. I hope it doesn't revert back.
Hooked up ELM327/Torque app to test electrical output. The dips on the graph I once had under load have become smooth.










This does not require removal of any wires. I chose to piggyback the existing factory wire over new cable. Contact points were stripped to bare metal and coated afterwards.
 

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That's interesting, and I would be interested in hearing if it lasts. Did you get the dimming and dips in output only at idle, or all of time? A computer reset could provide a stronger/higher idle which would explain smoothing everything out, but it is weird that the other cables you replaced didn't produce the same result.

I don't have any electrical modifications and I notice the dimming of interior lights at odd times, so I may check my garage for some heavy duty cables.
 

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Discussion Starter #3 (Edited)
The lights dimmed and at idle only. And only under very loud (stereo) conditions.
The idle speed has not changed.
Changing the other 3 cables did prevent the exterior lights from dimming.
Removing the firewall to transmission cable, cleaning to bare metal, reinstall, might actually help on it's own. It seems a lot of the body electronics rely on that ground. It's barely adequate when new. After a decade+ worth of corrosion (resistance) and that ground is less than adequate.
 
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