Hello folks - i have recently become caretaker to a new-to-me '95 XJR. Very happy that the car is fairly clean & not rusty as I've sadly grown used to that here in the midwest. At any rate, the car is gorgeous, even when it's broken. It seems to start and idle well, power seems fairly consistent but the O2 sensors in bank 1 seem to be having a conniption as you'll see in the screen grab from my OBDII Fusion app:



As you can see the pre-cat sensor in bank 1 is more or less stuck at about 1.3V, and the post-cat sensor isn't even trying. I figured if it was an intake vacuum leak, both banks would be doing weird things... I had previously read about the potential for the exhaust manifolds to crack, so i popped the chrome beauty cover off on my lunch today. Well well well....

Bank 1:


Bank 2 not quite as bad:




Gonna try to patch these up at least temporarily to see if it resolves anything. Not sure how long they've been like that, but if the ECU has been dumping fuel into bank 1, it's possible the O2 sensors are toast anyway. We shall see!

 

I can assure you that your oxygen sensor needs to be replaced. When was the last time you replaced them?

The crack in the exhaust wouldn't cause such an extreme failure.

I'd start at the oxygen sensor. (and I'd change them all) For now you can try to use Blue Magic Quiksteel High Temp Crack Repair....at least temporarily?

 

Mine was cracked where yours is on the fwd bank

Fortunately I think the manifolds are the same as with the more common normally aspirated models

Genuine Exhaust Manifold-3.2/4.0 Litre For Jaguar Xj 1995 - 1997 (from 720125 To 812255) Classic | Jaguar Land Rover Classic Parts

Look for EGR and secondary air manifold inlets if yours has them

There should be a couple of pairs in Kansas City to save on shipping

I need to extract a secondary air tube for myself and was looking at the donor car manifolds last time I was there

The O2 sensors are a titanium base and not the more common type as may be installed and your device can't read both types ( as they function differently ) at once

Bosch has a connector ready sensor replacement., Denso is the original and looks like the price came way down

O2 Sensor - Oxygen Sensors for Your Car, Truck or SUV (autozone.com)

The O2 sensor pigtail wires are very brittle, and my original had wires sticking out of the insulation

Use precaution on reassembly of the manifolds to not damage the donut gasket flange on the downpipe

 

Yeah I’m going to try the QuikSteel goop and see what happens. Then move on to the O2 sensors. From researching prior posts, I’m aware the sensors in these cars are… “unique” hahaha. I have no idea when/if they were ever replaced. Car has 150k on the clock. Jagbits appears to have sensors available. The less expensive Bosch 13789 appears to be unobtainium at the moment so Jagbits may be my best option for now. Will let you folks know how things turn out. I appreciate the help!

 

Auto Zone for O2 sensors

I have a couple of used spares

 

Only 2 of the 4 O2 sensors are used for engine regulation

The other 2 sensors are used as a comparison for Cat efficiency CEL code flag

So this gives you a swapping option

Front to back only and not bank A to B ( 1 to 2 terminology )

Keep careful track of original installation positions as this effects engine regulation

Quick Steel I think requires heat to cure so running the engine to do so may blow out before cure

The copper crush washers seem from reading to make a difference and new washers can be obtained from a cheep spark plug of 12 mm thread size different then your your spark plug 14 mm thread size

The sensor hex size is 17 mm

 

Your pic seems to show all 4 sensors with 2 wonky

The installation position terminology is here

So your only swapping option is .......................................

Need to determine is front or rear sensors are the regulation sensors

See page 81 first paragraph.

801S TITLE (jagrepair.com)

 

Do not swap sensors. Just ditch them. Parker is correct though, that the upstream ones are only there as a check. If there's no Check Engine Light, they are probably fine, but if you're not going to replace them, I would not touch them. They are on borrowed time as well, but may as well roll with it.

The downstream ones are the ones that have to go.

Try these:

 

Your final performance outcome will be short term fuel trim of target 0.0 % with warmed up engine coolant.

+ or - 3.0 % seems to be best expected from reading others

 

May thought on O2 sensor replacement is one at a time with some miles in between.

This allows the ECU to learn the fine performance of one sensor and slowly recover engine regulation

All at once may put the performance way out and you are probably already out

 

Yep that would make sense. One step at a time with this thing. It’s staying parked until I can address some of this because I don’t want to destroy the cats if it’s dumping fuel. I appreciate the insight. I did order 2 of the Walker brand sensors. Car currently has Platinum “+4” plugs in it so those are also getting tossed in the garbage and replaced with the plain old Champion Coppers just like the Land Rovers.

 

They changed the Champion heat range specifically for the supercharged version

From a 9 to a 12 or vice versa

May not be the final TSB

05.1-07 Amended (jagrepair.com)

May need a Italian tune up

 

bank 1 sensor 2 is literally pegged rich it can’t go any lower


post cat is the only thing that matters and it’s not getting affected by the crack. trim feedback loop only cares about the

downstream, upstreams were added as a hack to get some type of cat monitoring.

 

Ok, so - update.... the Walker O2 sensors on the Amazon link are like 4 weeks out, attempted an order at another vendor who claimed they were in stock but was refunded 3 days later due to no stock. Wound up finding a single used OE or OEM one on eBay and took a gamble with that. The cracks in the exhaust manifolds have been gooped with the QuikSteel stuff. Giving that about 48 hrs to cure since it's not quite summer here yet. We'll see how long that lasts. Spark plugs (RC12YC) came in as well and i swapped those out too. I'm not starting the car until i get the O2 sensor replaced.

Started working on the O2 sensor today - Post-cat sensor in bank 1. Oddly, it was a bit loose in the bung - not sure if that would have affected anything - but out it comes since i already have the replacement. Messing with the wiring behind the engine was actually the biggest pain. Once i finally made it to the connectors at the firewall, I referenced the photos below from a prior thread here that I'd saved. Can someone confirm that what is in these photos is correct? It seems to contradict the diagram Parker 7 posted above if you go by the color codes. I busted out the labelmaker and I'm going to label all these stupid things while i'm doing this.

Wiring for the rears?


Wiring for the fronts?


Currently, the sensor I removed from the Bank 1 Sensor 2 position was connected to the connector at the firewall with the 'blue' wire. Which Parker 7's diagram would say is correct, but the photo above would say is incorrect. I did also trace the pre-cat sensors and they match with the photo above. So now I'm unsure if those are connected properly or if they're reversed. Would like to confirm what is correct because someone may have goofed up the connections previously. Or - if the "re-orientation" procedure had been done previously, would it even matter? Or should i just leave things alone and reconnect the replacement sensor as-is and see what happens?

Many thanks!

 

swapped bank to bank oxygen sensors creates a feedback loop of death

these cars have 02 orientation feature because with how the harness is designed somebody had to figure out of a way to technician-proof it

 

Yes, it is possible that someone had switched things up before and used the Jag Tool to reorient the sensors, so the wiring diagram is certainly not foolproof.

A loose oxygen sensor could certainly cause the problems you were having.

 

A new threaded bong can be welded back in as a replacement , just a matter of acces

The bong in this case does not funtion as a ground path like older 3 wire O2 sensors

But it may have a undesirable effect on the sensor and it's output

the output wire is super sensitive and there is a ground post on the engine firewall for the return wire coax sheilding

this will be the smaller terminal post ( 2 ) with about 4 ground wires on it and not the larger B + post

But your original pic shows too much of a drastic difference

Just good housekeeping after repair of system

There is the possibility the pic I made for position by following by hand on the car is wrong

 

Well, possibly a bit of progress. I got the replacement used O2 sensor connected - i didn't swap anything else around at this time. Repaired a steering rack boot and rebuilt the rear trans mount too.

Got the car back on the ground and went for a drive. Still starts and idles fine. Waiting to see if the CEL comes back but at least it appears there is life in the Bank 1 sensors now per the OBD Fusion screenshot below.... gonna keep driving it and see what happens. Rear diff is on its way out so i can't go too far but that's a whole 'nother post.

If the CEL comes back, i'll start looking at electrical connections to clean and possibly dig out the homemade smoke tester...




Also, bonus Mercedes at brunch this morning:

 

Looks good to me.

While everything is fine, I'd start looking for at least two new oxygen sensors...so you'll have them when you need them

 

Well, I’m happy to say that after a week or so of driving the car, the CEL has remained off. Now… onto the next project…