[v12-engine] O2 Sensors - test & replace

My registration, due this coming month is to include a smog
certificate. California got really annoying with their smog process a
couple of years ago, so you don’t want to fail on a certificate run, or you
get to drive out of your way to get the car re-tested at a state-run
facility, and apparently have to deal with some PITA stuff for several
years afterwards. In preparation for this, I decided I should check and
replace a few things as necessary. Among them, the O2 sensors.

Well two Sundays past, I checked the output of the O2 sensors using a
scope, and found the B-bank to be sluggish (350-400ms swings), but
otherwise outputting the expected signal. The A-bank however, was
reporting the same signals while connected to the ECU (I tapped into the
signal with a tee), but NOT when it was disconnected, at which time I’d
get zilch.

So I figure the A-bank O2 sensor is shot, but the B-bank could probably do
for a replacement anyway. I’ve got to get in there and check the A-bank
signal again, this time from the ECU when the O2 sensor is disconnected on
that side.

The day after running the tests, I called Bosch, to inquire what their
application guide indicated the appropriate part was for this
application. I priced that down at the local “discount” autoparts chain -
Kragen. US$299. Ouch. Especially with the dealership quoting me US$160
for the SAME part.

I did some more calling around - Bosch won’t provide a reference of the
lamda/voltage values, saying that “that is published in the service guides
which Bosch Authorized Repair facilities get - call it part of the
incentive for them to become Authorized Repair facilities.” I did get the
Bosch numbers for a generic 1-wire, but they claimed not to have a generic
3-wire. Of course, the 1-wire sensors appear to average around US$25 for
generic, or even specific applications, but they aren’t suitable for my

So off I go looking in earnest last Sunday for 3-wire applications.

Bosch 13061 - mentioned in the J-L archives in the past six months at circa
US$40 - quoted at US$243.99 and $171.04, depending on what store I called -
and whether they actually had them.

Seems most of the heated types I was finding were 4-wire. I realize that I
SHOULD be able to just take the ground wire (the fourth wire) and wire it
to a good ground point, but seeing as they were a bit pricier than the
first two 3-wire matches I found, it wasn’t the choice anyway, extra work
and unnecessary wiring mods aside. BTW - I ran through a fairly diverse
list of mid-90’s model cars looking for a 3-wire app (expecting that they’d
be more common in later models), and was surprised to find that many were
still running with 1-wire unheated units.

I found a Bosch 13190 for a Chrysler (dunno WHAT Chrysler), at US$66.90

The real find (for me) though was a 1989 Ford Thunderbird 3.8L:
13942 - $44.99 8.5" leads (this is the one I decided on)
13953 - $59.99 16.5" leads

Of course, the store didn’t have TWO of anything (I ran into this with
spark plugs a while back too - one box of 8, but no more). So I had to
pick up one at this store, then walk a couple of blocks to the Grand Auto
(recently merged with Kragen) and pick up the one they had.

Savings on two O2 sensors: US$500 (or, US$230 off of Jaguar price).

The new Bosch units are supposed to have 60K mile service life. Dunno what
the originals should have been, but I rolled past 60K just last year. Mind
you, it isn’t as if this replacement was spurred by a sudden sluggishness
or economy change - I’m fairly certain these were shot when I purchased the

The new O2 sensors come boxed with a plastic cap over the O2 sensor tip
itself (you remove this right before installing), and they also have a glop
of anti-seize lube right on the threads (so no need to worry about needing
to pick up a tube specifically for the O2 install, though it is good stuff
to have in the toolbox anyway).

I carefully considered the possibility of swinging by the Ford dealership
on Monday to inquire about a mating connector for the O2 sensor (If I
simply picked up a couple of these and soldered them to the existing upper
O2 harness (from the original O2 sensors - not the automotive side of the
harness), I could then just pick up another Thunderbird O2 sensor and click
it in the next time I had to replace an O2 - no further soldering or
crimping or anything.

In fact, after doing the install, on a subsequent business day, I called
the local Ford dealership to inquire about the harness part. The shop guy
told me that it isn’t really a ford part (that is, their service department
isn’t getting the bit from Ford, but rather, an outside vendor). He didn’t
disclose the vendor name, but the OEM part number is #927082, and the
dealership charges $19.08 plus tax. Comes with about 8" of wire on
it. Two of these wired to the original Jaguar harness connectors (from
your old O2 sensor), and you’d be able to just plug in T-bird O2 sensors in
the future, all without sacrificing “original” parts on the car - since if
you get the urge to run OEM, all you’d have to do is pick up a couple of
OEM spec O2 sensors and plug them in at the main harness.

I wanted to get the job done, so I disassembled the T-bird harness
connector (reached in with a narrow tip needlenose pliers and pulled a red
coloured wedge from the middle of the connector, then gently pried the
locktabs, and slipped the wires out the back of the connector. This
accomplishes either one of two things, depending on how you’d proceed: it
gave me the maximum wire length as compared to simply cutting the wires at
the base of the plug (sure, a whole extra 1/2 inch, but every little bit
can count, since I opted to get the short one), AND it allows be to use a
MOLEX-like socket to just plug the wires into (then double-shrink in shrink
tubing to insulate the connectors from each other). The object is to
hopefully avoid having to cut the wire itself at all later on, something I
noted was a concern for people who were retrofitting generic sensors - each
time they’d cut their original harness wires to solder a new one on, they’d
have a little bit less than before. Here, that won’t happen.

I ran out the local electronics supply store and picked up some nylon mesh
tubing (diameter expands when you bring the ends near each other, and
contracts as you pull them apart) as well fibreglass insulation tubing, and
0.062" Molex terminals (a perfect fit for the Thunderbird terminals) - you
need SIX femal terminals, but the box was 10 mated pairs. I also picked up
some teflon wire (about six feet of black, and twice that much white),
though I didn’t end up using it for the new harness.

I chopped the original (Jaguar) harness about 4" from the O2 sensor, to
leave some room for later tinkering (I’m going to see if an indstrial
ultrasonic cleaner does anything for the old sensors), then soldered the
female molex terminals onto the old harness, and encased these entirely in
the appropriate gauge of shrink tubing. I also insulated the O2-side pins
with shrink tubing (except for the conductor shafts). After feeding the
original harness through an appropriate length (approx 14") of fibreglass
and nylon mesh, I plugged each terminal into the O2 sensor, and
heatshrinked over the joints. I then fed the wire back through the
insulator (with the grommet already in place), and reinstalled on the car.

The idle seemed better right away, but I’ve had a set of Magnecor 8.5mm
spark wires I’ve been putting off installing, and so I went about
installing them.

That was a mistake (no, not getting the Magnecor, just trying to install
them right then), as I have a stumble, which (using the dollar bill test at
the exhaust), is on the A bank.

I posted separatley on that last week, and promptly got a reply indicating
that I should check my injector harnesses, and sure enough the A5 inkector
harness wasn’t solidly seated. Reseating it resolved the idle stumble.

I took some digital pix (including of where the O2 sensors are on the
exhaust as well as the wire connectors in the engine compartment), and as
soon as I import them, I’ll see about posting the details to a webpage. I
still need to make time to head out and check the O2 readings on a scope
now that the new sensors are installed, and these readings, as well as the
originals, will also be on my site.

Sean Straw '88 Jaguar XJSC 5.3L V12 (LHD)
Marin County, California '69 Buick GranSport 455 V8