Date: Wed, 6 Aug 2014 21:40:26 -0700
Reply-To: Robert Keezer <warmerwagen@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Robert Keezer <warmerwagen@YAHOO.COM>
Subject: Re: Digifant II O2 sensor....My questions answered...
In-Reply-To: <CAHTkEuLREt=i4rerPRsaoQJ+iER2MgGcNHVY47JG0p+p0ZxFMw@mail.gmail.com>
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Were you using the 4-wire O2 sensor that came with the ABA?
The Motronic Mk3 O2 sensor is different from the Digifant O2 in that it has an extra wire(gray).
The Motronic O2 sensor grounds internally through the gray wire. The internal ground for the O2 is connected to the ECU, not the vehicle frame ground.
Unlike the Digifant O2, The Motronic O2 is not externally grounded.
The Motronic 4-wire O2 will not function with the gray wire ungrounded.
When I upgraded my 82 Westfalia with the ABA and Digifant 2, I didn't understand the purpose of the 4th gray wire, so I left it disconnected.
I failed the emissions test. I scanned the fault code memory of the ECU and "no O2 sensor" was displayed.
After studying the Mk3 Bentley, I saw the diagram showing the gray O2 wire connected to the ECU.
Robert
1982 Westfalia
>________________________________
> From: Don Hanson <dhanson928@GMAIL.COM>
>To: vanagon@GERRY.VANAGON.COM
>Sent: Wednesday, August 6, 2014 8:58 PM
>Subject: Digifant II O2 sensor....My questions answered...
>
>
>The vehicle and motor..84 Vanagon with Inline VW...a 92 cabriolet 1.8 liter
>head and everything else mounted on a 93 2.0 liter ABA block. I kept the
>digifant engine management and used the 1.8 liter head because it fits into
>the vanagon using VW diesel engine mounting system and no bumps or raised
>rear deck..A lot of the parts are directly from a vanagon digifant system...
>
> So my O2 sensor failed...perhaps because the wiring is/was aged and
>brittle and maybe shorting out....I had another spare one. the same 4 wires
>but not the VW plug. "We" deduced that the plug I had been running matched
>the 92 Cabriolet wiring diagrams...so anyhow I wired in the other 4 wire O2
>sensor and that worked fine for a few days, then IT failed also, or the
>wires shorted out again, or perhaps the wires shorted out and caused the
>second O2 sensor to fail also...I don't know for sure, but that seems
>likely.
>
> I looked for that particular O2 sensor with the proper plug, briefly,
>but after seeing them priced way up there ($75+) and considering the state
>of the wiring from my engine harness out to the existing plug...I decided
>to simplify with a less expensive single wire Bosch.(<$30) I got one
>from our Van Cafe California Vanagon supplier, who's tech told me it would
>work just fine...and so it did/does. I had a question on whether to
>attach the old ground wire from my computer to something...nobody really
>seemed to know, for sure..so I capped it off, along with the two wires to
>the heating element, which the single wire Bosch does without, also.
>
> So I eliminated that sketchy plug and 3 rotten wires and simply spliced
>to the signal wire, after cutting back that shielding a little to get to
>wires in decent condition. The van ran just fine without any O2 sensor
>connected, but very rich and my fuel mileage dropped to just 18mpg.. In
>order to know if the O2 sensor I installed, rather than trying to test pin
>outs or millivolts with a meter, I figured I'd just run a tank of fuel
>through and see how far I got, thereby knowing if the sensor was working,
>and if there was any decline in function using a single wire one rather
>than the expensive heated one that cost about 4 times more. Happy to
>report that I am back to my previous long time confirmed fuel consumption
>with this tank giving me 25mpg driving some city but mostly rural..
>
> I do not have a cat convertor in my system and the O2 sensor is right
>near the exhaust manifold, so it heats up quickly, I guess, judging by no
>decline in fuel economy...
>
> Thanks to all who tried to help me with this...electronics in the engine
>are not my forte... and I have to say any time I can eliminate 3 wires
>and two plugs without any downside...I am all for that.
>
>
>
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