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O2 sensor green coax shielding ground location?
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sasmith
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Joined: January 11, 2015
Posts: 51
Location: Latta, OK
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PostPosted: Thu Apr 06, 2017 4:32 pm    Post subject: O2 sensor green coax shielding ground location? Reply with quote

Can someone explain why the O2 sensor green coax shielding grounds through the #6 pin by a jumper wire with the DIGIJET system? That #6 pin wire runs to the #4 pin on the AFM, per Bentley. Obviously that must be grounded somewhere, but it would seem that wiring the shielding to pin#7, which is a more direct route to ground would make more sense. Is pin#6 grounded internally through the ECU? I have an early 85. In the Bentley, it shows that pin#6 is a white wire pre 85, and then it transitions to a green wire in 85. I guess mine being early 85, the wire transition had not happened yet, because mine is white, which was a bit confusing at first since I guess this white wire is a ground for the AFM?
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ohhorob
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PostPosted: Thu Apr 06, 2017 5:03 pm    Post subject: Re: O2 sensor green coax shielding ground location? Reply with quote

sasmith wrote:
Is pin#6 grounded internally through the ECU?


Yes. On digijet, the PCB pads are directly connected by the ground plane.

Image may have been reduced in size. Click image to view fullscreen.


And you might note that pin 25 is wired to ground, but in the ECU itself, there is a diode between the pin 6/7 ground, and the pin 25 ground.

I'm not sure why, but my guess is that diode provides protection from incorrect wiring or stray induced voltage from a disconnected AFM wiring harness??
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"Gundy" - '85 Westfalia
GoWesty 2300cc, Digijet
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sasmith
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Joined: January 11, 2015
Posts: 51
Location: Latta, OK
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PostPosted: Thu Apr 06, 2017 5:33 pm    Post subject: Re: O2 sensor green coax shielding ground location? Reply with quote

Cool. Thanks for the pic and the explanation. That will at least help me feel better as I am soldering a new coax through pin#6. I know that was from factory but I wasn't sure if a modification would be better. Not that I would now, but it does sound like you could wire the shielding through pin#7 and be fine. So are just 6/7 and 25 connected by the ground plane with the diode in between?
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