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Old 03-16-2003, 08:50 PM   #1
DanThom
Scooby Newbie
 
Member#: 23396
Join Date: Aug 2002
Chapter/Region: MAIC
Location: PA
Vehicle:
2003 WRX Sedan
Silver

Post Legacy ground "mod"

I've been reading about the "grounding mod" and decided to try it on my wife's '98 GT with some terminals and wire left over from a stereo install.

I started by measuring voltage differential to and from all of the factory grounds I could locate. The ones I could find are as follows:

[AC] - Alternator Case
[MG] - Main Ground point on back of engine
[BA] - Negative terminal of BAttery
[IM] - Intake Manifold
[DF] - Driver's Front side above headlight on radiator support
[DS] - Driver's Strut tower
[PF] - Passenger's Front on ABS motor bracket
[PS] - Passenger's Strut tower

I measured from ground point to ground point with my DVM and noted the DC voltage across each "circuit". The results are as follows:

[AC]->[MG] 7.0mv
[MG]->[BA] 7.3mv
[MG]->[IM] -1.9mv
[MG]->[DF] 11.0mv
[MG]->[DS] 11.0mv
[MG]->[PF] 9.6mv
[MG]->[PS] 11.5mv

Two points of interest:
The negative reading on the [MG]->[BA] "circuit" tells me that, on this car, the Intake Manifold is a better grounding point than the Main Ground point.
The body of the car gets its ground from an 8 gauge wire running from the "-" of the battery to the ground point on the radiator support. When I disconnected this wire from the firewall the results are the same as pulling the negative terminal off the battery.

I used 8 gauge wires to make the following grounds:
[MG]->[IM]
[MG]->[BA]
[BA]->[DF]
[MG]->[DS]
[MG]->[PS]
(I ran out of wires and couldn't do the [MG]->[PF] run)

Here's my results:

[AC]->[MG] 7.0mv (not regrounded)
[MG]->[BA] 3.8mv
[MG]->[IM] -1.7mv
[MG]->[DF] 4.6mv
[MG]->[DS] 5.2mv
[MG]->[PF] 7.6mv
[MG]->[PS] 5.0mv

I expect to see [MG]->[PF] drop more once I ground it. I'm also looking to run a wire from the alternator case to the main ground point, but I'll have to figure out how to attach to the alternator first.

Initial impression is that the car runs smoother, quieter, and seems more "effortless" when accelerating and cruising. Additionally, the lights seem a bit brighter and the car turns over quicker when starting. Overall a low-buck, low-effort mod that seems to have a few positive results with no apparent negatives. Time will tell.
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Old 03-16-2003, 10:54 PM   #2
sovereignmk1
Scooby Specialist
 
Member#: 11858
Join Date: Nov 2001
Chapter/Region: NWIC
Location: Spokane Valley WA
Vehicle:
1998 Silver Legacy

Default

Very nice write up. Makes me want to go spend 10 bucks to do this

//Mark
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Old 03-17-2003, 09:23 AM   #3
Legacy777
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Member#: 4800
Join Date: Mar 2001
Chapter/Region: TXIC
Location: Houston, Tx
Vehicle:
1990 Legacy & 97 OBS
AWD 6MT EJ22T AWIC Swap

Default

Yes,

Very nice write-up, and some numbers behind things.

Thanks
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Old 03-18-2003, 12:00 AM   #4
anotherB4
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Member#: 6120
Join Date: Apr 2001
Location: Tokyo
Vehicle:
BE5B AVOed B4-RSK
Sorta White

Wink huh?

There are still peeps who have not done this?

Oh yeah of little faith!

edit to add:
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Old 03-18-2003, 12:10 AM   #5
sovereignmk1
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Member#: 11858
Join Date: Nov 2001
Chapter/Region: NWIC
Location: Spokane Valley WA
Vehicle:
1998 Silver Legacy

Default Re: huh?

Quote:
Originally posted by anotherB4
There are still peeps who have not done this?

Oh yeah of little faith!

edit to add:
It's not the matter of believing it; it's me and wiring skills aren't a great working pair.

//M
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Old 03-18-2003, 08:36 AM   #6
Monas
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Member#: 31418
Join Date: Jan 2003
Location: Melbourne FL.
Vehicle:
1999 2.5RS
silver

Default

i just did this mod over the weekend. I was going to go to my local car audio place and get some nice pretty 8ga wire that had a smoke colored insulation, but they were closed before i got there . so i ended up using some 10ga crap wire from ace (just to hold me till next weekend when i can get some decent wire). I was gettting really sick of the flat spot at 3500-4500 rpm. so i wanted to at least see if it would work with that. i am not going to go into detail on where i ran all the wires, but i ran three wires all together.
Results
at first it didnt seem much diffrent but as i drove her the flat spot began to disappear. it was odd, the more i romped on it thru that range the better it got . well anyway, it is 70 miles later and the flat spot isnt even noticable even from the first start of the day.
I am going to go and get some better wire and rerun the grounds i did and add some of the ones from the first post on this thread and see if it gets any better.

well thanks to whom ever started this originally and to all those that have posted about it

Monas
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Old 05-01-2003, 02:41 PM   #7
krzyxkrean
Scooby Newbie
 
Member#: 30889
Join Date: Dec 2002
Location: renton
Vehicle:
1999 legacy gt
white

Default how much wire?

how much wire was required to do all the grounds you did? and how much more to do the rest of them? i want to do this mod soon, but i don't really know all the parts and stuff that i'll need. any help?
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Old 05-01-2003, 02:43 PM   #8
krzyxkrean
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Member#: 30889
Join Date: Dec 2002
Location: renton
Vehicle:
1999 legacy gt
white

Default

nevermind, i found another post with some info, but they didn't do all the grounds that you had done...
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