So I'm thinking about replacing these - to try to sort out my emissions problem - and have recce'd the job.

RHS seems fine and LHS looks like a PITA as so many of you say. Given I have access to a ramp, is it possible to do the top (upstream) sensors from below?

 

No, having done the job with Stu1986 a couple of weeks ago, the thing the ramp gives you is access to the bottom of the CAT - rightfully called a PITA for this reason. An offset O2 socket helps.

 

so there's no alternative to dismantling the coolant header tank and the heat shield. Okay...

 

I'll have to take a look but I think the only "easier" way is to remove the cat entirely and pull from out of car. If I recall correctly the top cat bolts are not too difficult to reach.

Not sure that counts as easier....

 

I follow that you are chasing an emissions problem but what made you decide the 02 sensors was the cause. Generally the OBD reading would tell you if a sensor has gone south. Do you currently have codes directing you to the sensors or just a smog test failure.
OBD readings are the first place to start and then looking at Short term fuel trims and Long term fuels trims are next. The sensors may be working and trying to overcome a different problem.
02 sensors are a PITA but even more so if they don't resolve the problem.
What are you OBD codes and symptoms.

 

Reason for starting this is an MOT failure ten months ago - had the car on Autologic during the summer (Jag Indy Specialist) and the only parameters he could see which were out of normal range were the upstream sensors.

Don't know what else to do. It's been off the road for almost a year.

 

Look at OBD live data. Start with every sensor you can and check it has plausible data. (E.g. temperature ones.)

Then get engine hot and look at fuel trims (see the endless threads).

Maybe you'll see something that's wrong and helps.

Cheap, fairly easy, DIY.

 

believe me, I've spent many an hour looking at OBD data and Fuel Trims. Till they danced in front of my eyes.

Hence my visit to my AutoLogic guy - and the only thing he came up with was the upstream sensors. So - I am pushing ahead with replacing those.

 

I am not trying to sway you about your decision but I know from experience that throwing parts at the problem will eat a large hole in your wallet. You should be able to pull the OBD codes fom the car and that will give you a better place to start resolving your problem. From the shop tech manual there are over a dozen codes associated with the O2 sensors.
Have the codes read and post the number Pxxxx and we can help you in your quest. Also, when you didn't pass the MOT what was the reason?

 

No codes

CO is 5%. That's my problem.

 

Hi jayartibee,

High CO readings when hydrocarbon and NOx readings are normal indicates the engine is running rich. Typical suspects include the engine coolant temperature sensor (ECTS), obstructed air filter or air intake, high fuel pressure, a failed fuel pressure regulator diaphragm, leaking fuel injectors, a problem with the MAFS, a problem with the crankcase breathing system, fuel in the oil, a failed-open carbon canister purge valve, a problem with the air injection system (on cars so equipped), etc.

As JagV8 implied, if the ECTS fails at a resistance that tells the ECM the coolant is cold, or if there is a problem with its electrical circuit, the ECM will continue to apply cold-start/warm-up fuel enrichment even after the engine is hot, a classic cause of rich running. You can easily test the CTS and compare its resistance with the chart in the Engine Management System manual:



You can download the manual here:

Jaguar Service Training Course 881: V6/V8 Engine Management

Cheers,

Don