From digest.v7.n29 Thu Jul 31 17:15:55 1997
From: Mike Daun <daun_at_nicmad.nicolet.com>
Date: Thu, 31 Jul 1997 08:58:26 -0500
Subject: Re: <E28> Oxygen Sensor

>1. The car has 130K miles on it and still has the original O2 sensor, as far
>as I can tell. Is there any chance in hell that the original is still good?
> The car passes emissions testing by a wide margin. I don't have a digital
>meter to test it with. Is there any "quick and dirty" test that doesn't
>involve a digital meter? Will an analog meter produce any meaningful result?

I'd be very surprised if the original sensor was still functioning at 130K. They usually die around 60 - 80K. You can use an analog meter to test the sensor if the meter has a 1V scale, most don't. When the sensor is functioning properly, you see a voltage that fluctuates from around 0.2V to 0.8V every couple of seconds. One thing to try, unplug the sensor and check your gas mileage. When unplugged, the Motronic defaults to 0.5V level for the 02 sensor. If your mileage improves, the sensor is probably bad.

>2. The exact factory replacement part seems ridiculously expensive (about
>$150). I have heard that it is possible to buy a universal 3-wire and splice
>the original connector. Is there any downside to this other than the extra
>work and the possibility of poor splices?

I've installed aftermarket sensors in my 535 and never had any problems. Just make sure you get a good connection and insulate it with heat shrink tubing.

>4. Is it necessary to buy the special slotted O2 socket or is there another
>way to get the thing off? Am I likely to tear the threads out of the cat and
>if so, what do I do, other than buy a new cat?

I bought a Sears deep well socket and ground two flats on the sides. This allowed me to put a wrench on the socket with the wire poked through the hole for the ratchet. Works fine, reasonably cheap. I always spray the threads of the sensor with WD40 and let it soak for a while before removing it. Make sure the new sensor has some anti-sieze compund on the threads (but don't get any on the sensor tip)

>4. I have heard that one of the symptoms of a bad sensor is poor mileage.
> What kind of mileage should I expect in this car (city/ highway/ average)?
> Since I have owned it, the car will do about 21mpg highway, 16 mpg city and
>about 18 avg.

This sounds a bit low. I can get at least 24 MPG highway depending on speed and 18 - 20 in mixed driving.

Good luck,

Mike

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Mike Daun (daun_at_nicmad.nicolet.com)
Nicolet Instrument Corporation
(Phone) 608.276.6124
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