O2 Sensors replaced: It's a puppy again!

[Dan Z. Johnson]

I just replaced the O2 sensors in my '95 90q. The car is at 110k now,
and i last changed the sensors at 65k. What an incredible difference!
You really do not notice the slow loss of response that old sensors
cause, until it gets pretty bad.
For those who have not performed this task, I heartily suggest that you
do so. Here's what was involved for my engine:

Go out to Autozone and buy two Bosch 13913 Oxygen Sensors. They may only
stock one at a time (happened to me, don't ask why, they don't know).
This is the "generic" sensor. it is the same as the OEM sensor, but does
not have the Audi plug. They will cost $37.99 each. You will solder
splice this connector to the existing wires that went to your old
sensor. If you are phobic about soldering small wires, pay $149.99 each
and you will get the same sensor with the correct Audi plug on it. Also
get an assortment of heat shrink tubing. If your Autozone doesn't have
heat shrink, Radio Shack does.

Locate the existing sensors in your car, screwed into the exhaust
manifold on either side of the engine. They look a bit like spark plugs,
but will have three wires (two white, one black) with a loose sheath of
rubber tubing. The white wires are for the heating element, the black
wire sends the voltage signal to the ECU.

Using a 7/8 or 21 mm crow foot and an extension, remove the sensors. The
passenger side will come out easily, as there is enough room to work.
The driver's side is another story. You will need one of those universal
joints for your ratchet, two extensions, small hands and a vocabulary of
choice words. If the sensors have been in there for a while, loosen them
while the engine is hot. Be careful, though. the sensors will be HOT,
too hot to touch. Use more choice words. BTW, Autozone will rent you the
socket tool for removing, installing the sensors. I think that the
rental is free, with a deposit. I had the crow foot, so I used that.

You can either unplug the sensor from the car and do the rest of the
process at your work bench, or leave them plugged in. I left them
plugged in.

Cut the wires, close to the sensors. Leave the sheathing on the wires,
you may need to trim it back several inches.
Remove the new sensors from the box and leave the clear cap on. The cap
protects the sensor and threads. The threads are covered with an
anti-seize compound. Your do not want to get the anti-seize on the
sensor itself.
Cut the plug off the new sensor (does anyone know what type of connector
this is, and how to get the mate?).
Strip half an inch on all conductors, including the new sensor.
Cut some heat shrink of sufficient length and girth to cover the slice
(About twice the thickness of the insulated wires) and slide onto each
wire that comes from the car side.
Cut a piece of heat shrink of sufficient size to span the gap between
the loose rubber sheathing on the new sensor, and the old piece still on
the car leading back to the ECU. This gap will be where the splices will
be.
Slide this heat shrink as far away from the splice area as possible, to
avoid it shrinking from the heat of the solder gun. I pulled it back
towards the ECU, bunched up the sheathing, and held it there with with a
hemostat. You could also use tape, but it would would not be as sexy.
Using an overlapping (inline?) splice, connect the new sensor wires to
the old wires leading to the ECU. Connect white to white and black to
black. It doesn't matter which white wires you connect together.
Solder the wires, allow to cool.
Slide the heat shrink down over each splice and apply heat to shrink. Do
the same with the outer sheath heat shrink. Heat can be applied with a
lighter, but do it indirectly and be careful not to burn the insulation
or set the car on fire. You could also use the car's cigarette lighter,
but that would be a  slow process. Resourceful and funny, though.  I
used a heat gun and it took a couple of seconds per splice.

Remove clear caps from the sensors and install. Tighten to 37 ft lbs.

If you know how to solder, this whole process shouldn't take more that
an hour.

Of course, the sensible thing to do would be to locate some used
connector ends at a junk yard and have a spare set on hand!

I'll be helping a friend change the sensors on his 100 soon, I make a
few photos then. Should help explain it a bit better.

Some links to help:
Google search:
http://www.google.com/search?hl=en&ie=ISO-8859-1&q=Bosch+oxygen+sensor

Very, very good 12v Pages step by step:
http://dev.12v.org/repairs/o2sens.php

Bosch pages:
http://www.boschusa.com/AutoParts/OxygenSensors/

SAE site:
http://www.sts.sae.org/membersonly/techinfo/servicetech/oxygen13-17.pdf


-DanZ