Replacing AJ6 Oxygen Sensor
 

Hey folks,

I'd like to attempt changing out the O2 lamda sensor (singular) on one of my '93s this weekend. I have the Bosch replacement part, and the job seems simple enough, if possibly difficult to access.

If I put the front on a pair of ramps, should I be able to access the sensor (over the top of the collector) from below?

Both my cars have either a cardboard or foil wrapper around the sensor; the replacement part doesn't include anything like that. Is that removable/replaceable? I presume I need to move it somehow to get access to the sensor nut.

Anything else I should know? :icon_rally:

If I recall correctly, the two upstream O2 sensors are accessible from the top, passengers side of the engine bay.

The two downstream ones are accessible only by sliding underneath and getting a wrench on it, blind.

I thought one of the clear benefits of the I6 is the easier access to typically hard to reach components like this. You should easily be able to spot the two upstream sensors from the engine bay..no?

Thanks, Vee.

My understanding of the AJ6 vs the AJ16 is that the older engine only has a single O2 sensor, unlike the later motor which has four. The AJ6 sensor is clearly visible from above, but it is at the very bottom of the bay just ahead of the manifold exhaust flange.

"..sliding underneath and getting a wrench on it, blind" is exactly how I imagine this is going to go. However, I'm hoping this still compares favorably to changing the plugs on a V12.

:icon_troll: :icon_wink:

Kurt

The number of lambda sensors varies by market. My AJ16 has only 2, located in the downpipe. Anyway, a couple of suggestions.

- If you're not keeping the original sensor, then cut its wire close to the sensor. You can then use a proper socket to remove it. This is quite important as it can be VERY tight. So using a socket will avoid you damaging the head and giving you further problems.

- Once the old sensor is out Check and clean the threads of the mount in the downpipe. They can get quite corroded. You might even have to retap them.

- If you use copperease or similar on the threads of the new sensor, be very careful that nothing can get on the nose of the new sensor as this will ruin it.

Good luck

Paul

I can add two oddities:


1. The one on the pipe of my 4.2 XK engine was loose enohgt o leak and be removed by hand, no tool needed.


2. The ones on my donor lump engine were super tight. In the open, I got them loose with a lot of torque. I used antiseize on the new ones I installed.


I dimly recall that a special wrench/socket is available. why, I don't know, I didn't need one???


Carl

The special socket has a cutout to enable it to be fitted with the wiring in place. Otherwise, obviously you can't put a socket on the sensor with the wiring plug in place.

Paul

I recall being able to put an open end wrench on it...all four of them.

I totally forgot I actually own the proper socket to remove O2 sensors. I guess I would have remembered had I needed it.

Thanks for the excellent advice, Paul!

I'm not sure I would have thought to cut the wires on the old one, although that will still require a very long socket.

To be really clear, though, let me say that on both my '93 AJ6 4 liter(re) engines, the oxy sensor is on the top of the very back portion of the manifold, almost under the firewall at the very bottom of the engine space. This is not located anywhere that can really be described as a down pipe. In muscle car terminology, it's at the very back of the collector tube. You can barely see it from the top. I can hardly imagine getting an arm down there to remove it from above, but I may test that first.

From below, I'm not sure how useful a socket that tall is going to be, but I'm game to try it. I'm going tool shopping tonight, so I'm looking for a tall socket and a shorty open-end. Hopefully, one of those will work.

The new sensor comes with a plastic cap cover on the business end, and there are some very spare smears of black goo on the threads already. Some kind of thread compound, I imagine. Enough to leave it at that?

Also, if need to tear the existing foil shielding, is that replaceable or even something to be concerned with?

***Update: to correct myself, it is actually behind the line of the firewall, in the transmission hollow just before the actual transmission tunnel. No arm or tool is getting there from the top.

AJ16 has about the most accessible oxygen sensors I have ever had the honor of replacing!

I have a whole set of O2 sockets but sometimes they are too long to fit into tight spaces.

When that happens I use the off-set style sockets like this;

https://cimg0.ibsrv.net/gimg/www.jag...ed0e0d866a.jpg

Mark

Kurt,

Just to clarify, the sensor is not mounted in the manifold. The manifold is the two-part item. Mounted to that is the downpipe. This single piece item has two pipes that mount to the manifold and merges as one pipe which then joins to the next part of the system. Is that you refer to as a "collector"?

That black stuff should be fine as a jointing compound.

It is worth taking care when you remove the old sensor to avoid damaging the threads in the boss. With the pipe in situ, it's a pain if you have to clean or tap the threads (I know!)

Good luck. Let us us all now how you get on!

Paul

You know, I ought to know by now not to say "no way" without skinning at least two knuckles trying, beforehand. It looks like coming in from the top is the way to go with this engine after all. Also, I'm committed now because I did cut the wires on the old part. But first, PICS!

https://cimg3.ibsrv.net/gimg/www.jag...44576f9251.jpg
Close up of the current part with and without the heat sleeve, giving an idea of the location and access.

Some of you may notice that the sensor seems to be mounted in a bit of a dimple (spoiler alert!). Going with the short-tool-from-below plan, I found this nifty O2 sensor tool that I was really excited about finding:

https://cimg1.ibsrv.net/gimg/www.jag...fa1ae5b79d.jpg
Thirty bucks at Pep Boys. Would have worked really well, except for one fatal flaw.

This seems like it would actually have provided enough degrees of movement from below to ease out the sensor with some patience. However, it will not bite onto the cracker-thin hex nut (thanks, Bosch!) sitting down in that recessed dimple (thanks, Jaguar!); the substantial socket wall on this tool is simply too thick to get onto the nut in this application. So now I know I have to make a socket work, and there simply isn't room to operate any kind of socket blind from below (maybe if it was on a lift, not on a pair of ramps).

So it turns out you can put an O2 socket from above on this part with a single pivot and about 26 inches of socket extension. However, even a conventional O2 sensor-specific socket will not seat in this location.

https://cimg7.ibsrv.net/gimg/www.jag...895815d3b4.jpg
You can see the socket getting interference from the downpipe (thanks, Paul).

Ugh. I'm not certain the pivot angle will give me the torque I need to break this part loose across nearly 30 inches of driver extension yet, but I am hopeful this will work once I can get a tool over the hex. Plan C is a 'thin-walled' O2 socket:



Hopefully this tool can get down in that recess. I've been working beastly hours lately, but if I can get home at a decent hour Monday, I should have the tool on hand by then.

Indeed. I knew the AJ16 had the two-piece manifold, and obviously the AJ6 does too, but without the mini-cats there in the downpipe it's less obvious. The way the two exhaust flows are merged before the flange is reminiscent of the collector in a tubular exhaust header.

At the moment, I am unable to do anything more than gently caress the thing, so it's got nothing to fear from me! :icon_badrazz:

This car seems to have been garaged most of its life. The rust in this area of the exhaust is trivial. You can see in the photos that my application of penetrating oil after the first pics has already started to shine up the downpipe after a couple of hours. Fingers crossed on getting this sensor out clean!

Well, I went to some effort to get home at a decent hour tonight to work on the car, but I was shipped the wrong tool. The socket was mislabeled, and clearly not 'thin walled', nor did it match the Amazon photo. It's the exact same outer diameter as the tool that I already have.

:icon_stooge:

Funny, that special chrome wrench is the exact one that I bought, myself and...at Pep Boys, too...
Great tool, it worked perfect on my '94 AJ6.

Cheers,

The second socket I received from Amazon yesterday was also the wrong, mislabeled tool (which I half expected). I contacted the tool company, and they quickly responded! They said they had a batch of incorrectly packed tools come in. They apologized and are sending me a free replacement.

:icon_headbang:

That is both awesome and disappointing, at the same time. I knew that tool looked like a winner, and now I'm wondering why I'm having such a hard time getting a tool to bite on that sensor.

If this new socket doesn't cut it, I think I'm looking at dropping the downpipe as my next escalation.

Okay, the new 'thin-wall' O2 socket came in this week. The good news is that it does bite onto the old sensor. The bad news is that I can't break the old sensor loose with a pivot and 20-something inches of extension torque. The sensor is stuck in there hard; I'm twisting a considerable amount of force into those extensions without a budge. I'm concerned about trying to force this harder.

If I could get my hand over the top of the downpipe tube from below I might be able to use this socket without an extension. I'm going to make at least one more attempt to get at the sensor from below.

I've looked at the downpipe itself and I'm dubious about trying to remove it myself with casual tools and a pair of ramps. Access to the back nut on the rear pipe seems particularly tricky. I may have finally bit off more than I can chew without professional help.

:icon_cankick:

Can you attach that thing to some kind of impact gun? Sometimes the impact guns have an easier time of breaking up stuck on bolts.

Have you tried shooting some penetrating oil (PB Blaster, etc.) into the recess. If not do so and let it sit and do its thing. You could also try applying a bit of heat to the pipe. Oh, and +1 on the impact gun.