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 Post subject: Shielded Wire Replacement
PostPosted: Fri Feb 19, 2016 1:40 am 
Second Gear
Joined: Thu Oct 27, 2011 5:09 am
Posts: 452
Location: Dirt Roads, Colorado
Hello fellow members!

This topic is in the interest of replacing wiring in your vehicle that may require shielded wire. Often with the age of the first generation legacy's you may find that some of your wiring has become brittle or broken over time.

What is a shielded wire?
Some critical sensors in your vehicle may use a shielded wire to protect the signal received by the ECU from interference from other electrical components in the vehicle.
A signal wire(s) leading from the sensor to the ECU will have an additional uninsulated wire wrapping around them all the way to the ECU where it is grounded at one of the ECU pins.

What sensors use a shielded wire?
Knock sensor. Cam Position sensor. Crank Position sensor. Throttle Position sensor. Mass Air Flow sensor. Manifold Absolute Pressure sensor. Oxygen sensor.

Symptoms
Sometimes a wire that is brittle but may not be broken can cause an intermittent or full time CEL. The signal wire may have a crack in the insulation around it exposing the wire, thus potentially making contact with the shielded wire that wraps around it. Because the shield is grounded it will cause the ECU to have an improper reading.
You may have experienced this by replacing the sensor but still have a CEL.
Most commonly this is seen with the knock sensor.

Solution
Using a voltmeter you can perform a continuity test in helping to determine the exact location of the short. Start from the sensor and work your way back.
Sometimes the short may only be within a couple feet of the wire leaving from the sensor, usually in the engine bay where it is exposed to the most elements(engine heat, water, oil, dirt). You can cut out the bad section and replace it with new shielded wire. You may solder in the new wire(s) but it's recommended to use crimped connectors with heat shrink. Soldered wire joints can become weak over time and are not very flexible.
It's more rare but you may find that the short in your wire is within the car and is usually un accessible with out removing the dash and/or unraveling the wiring harness. In this case it can be easier to replace the wire(s) from the sensor all the way to the ECU. This may require a new routing of the wire(s). You can use an existing accessible hole(sometimes through a rubber grommet) in the firewall or drill a new hole.

Where can I buy shielded wire?
To purchase shielded wire I've found that shopping online is the best source. You should pick a matching gauge wire, most are 18awg.
I will provide some links and also some key words to search for incase the links become un viewable over time.

Google/eBay/Amazon key words:
Stranded shielded gray jacket PVC wire & cable. 18awg shielded wire.
18 awg cl3r/cmr/mpr shielded. 4/18awg shielded. 18awg fire/security wire.

Links:
ebay link
ebay link
omega wire
altex electronics

What it looks like
Image

Side notes
ECU codes
ECU pin out
how to use a voltmeter
how to perform a continuity test


* If any information appears inaccurate or you think i should add something, please inform me via PM.

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 Post subject: Re: Shielded Wire Replacement
PostPosted: Wed Mar 02, 2016 6:58 pm 
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Joined: Tue Oct 15, 2002 11:37 am
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Excellent post dankberries! Thank you very much!

I've also run across scenarios where the signal wire inside the shielded wire was broken. I personally would recommend running a new wire vs. trying to tie into the exiting shielded wire. By using completely new wire you help minimize the chances of future issues due to the old wire. It may be a little more work, but I think it'll be better in the long run.

I'm going to add this to the sticky compilation.

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1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

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 Post subject: Re: Shielded Wire Replacement
PostPosted: Wed Mar 02, 2016 11:58 pm 
Fifth Gear
Joined: Mon Mar 08, 2004 2:30 am
Posts: 2275
Location: Auburn, WA
Yup great write up. The only reason I have the purple car is that it's previous owner pinched the TPS wire while removing the engine. I had to run a new wire because it was shielded. It was the only thing wrong with the car that caused it to sit for months.


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 Post subject: Re: Shielded Wire Replacement
PostPosted: Sun May 29, 2016 12:51 pm 
In Neutral
Joined: Wed Apr 13, 2016 4:05 pm
Posts: 19
Location: Delaware and North Virginia
the one wire that has no shielding in pic above, seems to be called the drain wire, does it get connected to ground? I have a harness that will need several shielded wire repairs but I have not yet begun to tackle this. thanks.

I can't see it in the first pic on this thread...
viewtopic.php?t=37071


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 Post subject: Re: Shielded Wire Replacement
PostPosted: Sun May 29, 2016 6:17 pm 
In Neutral
Joined: Wed Apr 13, 2016 4:05 pm
Posts: 19
Location: Delaware and North Virginia
found a great page in a great thread that touches on shielded wire repair with lots of pics : )
viewtopic.php?f=25&t=40398&start=425


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 Post subject: Re: Shielded Wire Replacement
PostPosted: Sun May 29, 2016 10:22 pm 
Second Gear
Joined: Thu Oct 27, 2011 5:09 am
Posts: 452
Location: Dirt Roads, Colorado
jimkelly1964 wrote:
the one wire that has no shielding in pic above, seems to be called the drain wire, does it get connected to ground? I have a harness that will need several shielded wire repairs but I have not yet begun to tackle this. thanks.

I can't see it in the first pic on this thread...
viewtopic.php?t=37071



The single "uninsulated" wire the wraps around the four "insulated" wires would be considered the "shield" and should be treated as a "ground".

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93 impreza rally muffin
93 legacy ss Tarmac Terminator
89 Nissan 240sx sr20
90 Nissan 240sx 2jz
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Dank is actually German for "silly term which the kids have come up with to describe exceptionally choice marijuana.''


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 Post subject: Re: Shielded Wire Replacement
PostPosted: Sat Jul 02, 2016 4:55 pm 
Site Admin
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Joined: Tue Oct 15, 2002 11:37 am
Posts: 27230
Location: Houston, Tx
dankberries wrote:
The single "uninsulated" wire the wraps around the four "insulated" wires would be considered the "shield" and should be treated as a "ground".




I would like to clarify the above statement, the shield wire should be treated as a sensor ground only and should not be connected to a chassis ground. The shield wires are connected to a common reference ground in the ECU and if you connect that to a chassis ground it can cause you issues.

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surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm


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