Marvin the alien

Tried replacing the O2 sensors today with partial success.... and having done a bit of a search on the forum couldn't really find an answer, hoping somebody may be able to help and also that this may be of interest..
All four new sensors were purchased from Rock Auto, Bosch 13721 and 13723 and show the Porsche part numbers.
On the drivers side both upstream and downstream sensor wires were running through the oval grommet, new upstream sensors installed easily and hooked up, no issues, wire run through the oval grommet. On trying to install the new downstream sensor (drivers side) the wire was too short to run through the grommet by approx. 4 to 6 inches

At this point decided to only change the upstream sensors and button everything up with the old downstream sensors.

Has anybody else come across this issue and could anyone tell be where the downstream sensor wires should be routed if not through the oval grommet ?

Having done a bit more searching it seems like some people have only the upstream sensors running through the oval grommet while others have both running through it.
I can only assume that there may have been some form of design change, for reference my car is a September '95 build (OBD2) with Gillet cat.

Reason for changing the sensors was that they seemed to be a bit lazy, no O2 sensor codes but was having the occasional burnt match smell when hot (oil temp gauge at approx 9 o'clock) regardless of fuel brand and fill up location (always 93), slightly rough idle also a more noticeable "rocking" idle after a throttle blip. Old O2 sensor tips were white in color..

NeinNeinThree

I just did my drivers side ('97 C2) downstream about two weeks ago. My harness went through the oval grommet down and to the left of the engine, it would come out, laying under the car and facing towards back of vehicle by the drivers muffler, top left under vehicle. I used the Bosch with no length issues. When I was looking down and left in the engine bay, it looked like there could be two spots for the harness to go through, the one mine went through was further down and left, almost hard to see.

jmrdmd

How difficult was it to remove the old sensors? I’m thinking of putting in an X pipe.
Thanks
Jan

Marvin the alien

In this case it was easy, none of the sensors were corroded or stuck in place. Using the right tool helped a lot.
The passenger side plastic cover over the connectors was one of the more difficult aspects needing a bit of faffing around to get out. You may need to replace the rubber sleeves on the two bolted clips that hold one of the cables for each side. Mine, as others have found, were totally perished.

sacman

If I remember correctly, both side have different length of wiring. Did you install them swapped?

QN

Marvin the alien

Yes they have different lengths, 33" and 27" or so..
Triple checked the right sensors went in the right place. Upstream were fine. Downstream were too short to follow the "as they were" routing of the wires where both upstream and downstream wires went through the oval grommet. Seems that somewhere, somehow or at some time something changed..
Searching a few posts here it appears there are different wiring routes for the downstream sensors. Mine, had both upstream and downstream going through the oval grommet. Others have only the upstream going through the oval grommet (even though it has holes for 2 wires) and the downstream going some other route..
Of note one of the old downstream sensors had 13722 marked on it. I need to get the car back up on a ramp to see if I can find where the downstream wires can be routed.

pp000830

Not hard. The key is to
remove the body grommets the sensor pigtail wires go through,
then spray the sensors' mounts (bung) with a little acified penetrating oil such as PB Blaster. Let it sit overnight.
Then cut the wire at the sensor and slip a closed-end box wrench over the sensor body hex.
Hit the box wrench with a mallet and it will crack the sensor loose.
Use the old sensors' wires as a fish tape to pull the new sensor wire through the body to the connection box in the engine compartment.
Plug the pigtails into the corresponding wiring harness connector of the same color black or gray and reinstall the grommets.

One of the easier DIY efforts.
Andy

pp000830

Hi Sacman,
This is easy to check for in that the sensors' pigtail connectors are of different colors for the before CAT vs. the after CAT ones, one black and one gray. They plug into the corresponding sockets of the same color in the engine compartment.
Andy

jmrdmd

Thanks so much for the replies! How do you know if the sensors are bad?

71-3.0-911

Generally an O2 related check engine light. I went ahead and changed mine once I went over 110k miles. They can be bench tested but the MTBF of them is around 100k miles.

jmrdmd

Thanks! Appreciate the info!

Jan

pp000830

If a sensor is bad you will get a check engine light and a code for the sensor or other components in the exhaust system that rely on a properly working sensor.
A common one is for the sensor being slow to warm up. This code is related to age and debris that forms on the sensor. It usually shows up in the fall when cooler weather causes the sensor to take a bit longer to warm up into its operating range, Any oxygen sensor-related fault code should be first addressed by clearing the codes with a On Board Diagnostic (OBD) reader and seeing if it returns validating there is really an issue.
Here is a page on the subject:
https://993servicerepair.blogspot.co...anagement.html

Here is a page discussing OBD Code readers:
https://993servicerepair.blogspot.co...bdc-notes.html

Andy

Marvin the alien

Quick update on this for the record and interest.
September '95 build, 1996 OBD2 car. Car had 3 different sensor part numbers fitted (assume from new).
O2 sensors, as removed:
Upstream, before catalyst, black connectors, all the same length marked as 993-606-116-00.
Downstream Passenger side, grey connector marked as 993-606-118-00
Downstream Driver side, grey connector marked as 993-606-117-00 - This sensor had a wire length approx 10 to 11" longer than -118.
On drivers side both O2 sensor wires were originally routed through the oval grommet. No other wire pass through anywhere on the drivers side. So fairly sure that at some time there was a design change to two sensor wire lengths and an additional pass through added on driver side.

Would add that car now runs better, seems to be more eager to pick up. With 100 miles on new upstream sensors exhaust tips have turned to dark grey/black versus having a beige discoloration. It would seem the car can run to some degree lean without any codes showing up due to lazy or slow to react upstream O2 sensors.

hope this info helps others.