coclimber Posted April 23, 2014 Share Posted April 23, 2014 I tore apart the (2001 Legacy 2.5L) harness I'm working on. I was going to replace the shielded wires with new ones. The OEM Subaru wiring seem to be braided, not foil. I researched the difference and foil is more for blocking out high frequency interference and braided for blocking out low signals. I guess I'm wondering if anyone has used foil shielded wires instead of braided before? Because... foil is what I have on hand and I'd like to just use it Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 23, 2014 Share Posted April 23, 2014 The type of shielding probably isn't so critical on that car so long as its there and properly grounded. On newer cars with high speed networks the sheilding is definitely a major consideration since improper shielding can mess with communications between the modules. Kinda wondering why did you decide to replace all of the shielded wiring? Link to comment Share on other sites More sharing options...
coclimber Posted April 23, 2014 Author Share Posted April 23, 2014 The type of shielding probably isn't so critical on that car so long as its there and properly grounded. On newer cars with high speed networks the sheilding is definitely a major consideration since improper shielding can mess with communications between the modules. Kinda wondering why did you decide to replace all of the shielded wiring? Oh, yeah, that... well, its all about this Vanagon>> Subaru conversion effort I'm doing. The Subaru wiring harness is being converted to work with my VW Vanagon. In the process, I need to lengthen it, so I am messing with all the Subaru wiring now. Instead of splicing in the middle to lengthen it, which would leave the wire un-shielded there, I'd rather just use one continuous, new shielded wire and splice close the ends (e.g., connectors) where the shielding is less important. Jason Link to comment Share on other sites More sharing options...
coclimber Posted April 23, 2014 Author Share Posted April 23, 2014 The type of shielding probably isn't so critical on that car so long as its there and properly grounded. On newer cars with high speed networks the sheilding is definitely a major consideration since improper shielding can mess with communications between the modules. Kinda wondering why did you decide to replace all of the shielded wiring? Related to the "properly grounded" statement.... I could definitely could use more info here... Would these grounds be on the ECU or connector end of things? For instance, when I look at the O2 sensor's (a 2 conductor - blk and white wires - shielded cable) connector, I don't see where the shielded cable could be grounded. The black and white wires connect to the sensor connector and the braided shielding is just kinda ended... Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 23, 2014 Share Posted April 23, 2014 Grounding for the shielding is done through the ECU. There are joint connectors at various places in the harness which connect sections of shielding, some of those connect the shielding to ground through a pin on the ECU. Link to comment Share on other sites More sharing options...
coclimber Posted April 23, 2014 Author Share Posted April 23, 2014 Grounding for the shielding is done through the ECU. There are joint connectors at various places in the harness which connect sections of shielding, some of those connect the shielding to ground through a pin on the ECU. Thanks! OK. So, my plan to properly ground the new shielded wire will be this: ================================================================== 1. Cut the old, OEM shielded wire off near the ECU 2. Twist the old, OEM cable's braided shielding into a "ground" wire. 3. Use the drain wire in the new foil shielded cable and splice it onto the twisted/braided shielding, which should be grounded on the ECU. That approach should properly ground the new and old shielded cables together as far as I know. Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 23, 2014 Share Posted April 23, 2014 There should be a joint connector near the ECU that already has the shields joined to the proper pin. At least for the engine harness sensors. The MAF sensor IIRC has its own shield pin on the ECU. The shielded wires are easy to find since they're usually grey or black and have what looks like a splice near the end wrapped in tape or heat shrink tubing. Link to comment Share on other sites More sharing options...
coclimber Posted April 23, 2014 Author Share Posted April 23, 2014 Can I ask one more thing on this? Here's what I need to replace: 18 AWG 4 conductor - grey engine connector 18 AWG 1 conductor - grey engine connector x 2 18 AWG 2 conductor - O2 sensor 18 AWG 1 conductor - O2 sensor I cannot find 18 AWG, shielded, 1 conductor cable with a drain wire anywhere!! I found a product at an online aircraft supply store, but it did not have a drain wire to ground off the shielding, so I am hesitant to buy that for my needs. Should I just get more of the 2 conductor cable and use that for the three places I need to use 1 conductor? Obviously, I'd just not use one of the wires inside the cable...but at least it would have a drain wire. I think the worst that could happen is the final wire loom is a little fatter than it would be if I used 1 conductor. Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 23, 2014 Share Posted April 23, 2014 The dual conductor is also more expensive I'm assuming? All you need to do is strip back the insulation over the shielding, strip about 2" of insulation off of a short length of 18-22awg wire and wrap it around the shield section several times then heat shrink over it. 1 Link to comment Share on other sites More sharing options...
coclimber Posted April 23, 2014 Author Share Posted April 23, 2014 The dual conductor is also more expensive I'm assuming? All you need to do is strip back the insulation over the shielding, strip about 2" of insulation off of a short length of 18-22awg wire and wrap it around the shield section several times then heat shrink over it. Brilliant!!! Thanks!! Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 23, 2014 Share Posted April 23, 2014 Ill add, make sure the shielding is stripped back at least 1/2" from the center conductor, and the insulation on the drain wire overlaps the shielding by about 1/2". Link to comment Share on other sites More sharing options...
coclimber Posted April 23, 2014 Author Share Posted April 23, 2014 roger that... Here's the only options for 1 conductor, shielded that I found and it is all from aircraft stores, not automotive. But, I figured aircraft and auto are probably similar. Quite a difference in price! $.40/ft = http://www.chiefaircraft.com/aircraft/installation-supplies/wire/wire-18-1cs.html $1.38/ft = http://www.aircraftspruce.com/catalog/elpages/shieldwire.php Link to comment Share on other sites More sharing options...
presslab Posted April 24, 2014 Share Posted April 24, 2014 The drain wire is just for convenience, to more easily terminate the shield into a connector. It's not hard to strip back the insulation, un-braid the shield, twist it, tin the twisted shield, and solder it to the other side. For high-impedance signals like the O2 sensor, the exact cable isn't required. It's more important to get something that will handle the heat and vibration of an engine compartment. The wire gauge isn't needed to handle high current, it's more needed to have something that's not fragile. For things like CANbus the proper cable impedance must be used. Link to comment Share on other sites More sharing options...
coclimber Posted April 24, 2014 Author Share Posted April 24, 2014 The drain wire is just for convenience, to more easily terminate the shield into a connector. It's not hard to strip back the insulation, un-braid the shield, twist it, tin the twisted shield, and solder it to the other side. For high-impedance signals like the O2 sensor, the exact cable isn't required. It's more important to get something that will handle the heat and vibration of an engine compartment. The wire gauge isn't needed to handle high current, it's more needed to have something that's not fragile. For things like CANbus the proper cable impedance must be used. Well shoot. I just cross-posted about "heat" in another thread! But, since you mentioned it here.... I'll ask again - what temperature ratings should I be looking at for buying the cable for these engines? I have options to buy anything from 60 C, 75 C, and 150 C... big range. Of course it will also be in split wire loom to protect it as well. What can handle the heat output of a Suby engine? Link to comment Share on other sites More sharing options...
presslab Posted April 24, 2014 Share Posted April 24, 2014 Subaru uses PVC insulation, probably some cross-linked variant. I'd say 75-80C rating is sufficient for wiring in the engine bay, but not on the engine; wiring on the engine (under intake manifold) should be 125C. Link to comment Share on other sites More sharing options...
Crazyeights Posted April 25, 2014 Share Posted April 25, 2014 (edited) In most of the older harnesses that I have worked on I have noticed that the shielding is sometimes left floating at one end and connected to ground on the other. I have no idea if this helps you or not. I just happened to have several harnesses open at the moment. Edited April 25, 2014 by Crazyeights Link to comment Share on other sites More sharing options...
presslab Posted April 25, 2014 Share Posted April 25, 2014 Attaching the shield at one end prevents a ground loop. A ground loop is like the hum sound you can get with a home stereo. Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 25, 2014 Share Posted April 25, 2014 Ground looping can actually create interference. Minor differences in electrical potential at each end will cause alternating current to flow through the shielding which induces stray currents (interference) in the signal wire that you're trying to shield. Grounding the shielding at only one end allows outside sources of interference to be directed to ground without looping. Link to comment Share on other sites More sharing options...
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