Need help,
my xj8 1997 4.0lt has just failed the MOT(england) on the emmission's test. It failed on on 3 readings i.e CO, HC, and Lambda.

On the perivous MOT there was problem with the emissions test.
I recently had a new gearbox.

Can anyone throw any light

 

Jagman, sounds like your catalytic converter is not working as good as it could. So, it sounds like you need to install new catalytic converters into your car. That will fix all of your issues. I would also check to make sure that the air pump is working too. Without sufficient extra oxygen being placed in the catalytic converter, it can't get rid of the unburnt fuel and CO levels, which is causing your lambda (ie, difference between your in and out levels) to be lower than it should.

Any muffler/exhaust shop should be able to look at this for you and get you on the road again. I'm sure it is not what you want to hear, but that is what it is sounding like. Would you happen to have a little bit of a rattle under the car during acceleration or during higher RPMs of the engine? This can be a sign that you have damaged plates inside the catalytic converter, indicating that it is due for replacement.

 

Thank you for your reply.

I am taking the car down to my local garage. when i went to buy the car from the dealer, there was a rattle coming from underneath the car at the drivers sid door position

I had doubts on the cat after 110k. what sort of money are we talking about for a new cat

do you think the lambda sensor is faulty after 110k also.

 

thejagman, if you are going after a factory catalytic converter, stand by. According to http://www.jaguarparts.com (normally a pretty cheap place to get factory parts, they are a dealership in Cleveland, OH), you are looking from $800 up to $2500. Keep in mind that you have 4 catalytic converters under the car (2 primary, 2 secondary, with a primary then secondary on each side of the car). You don't mention if you have the V6 or the V8 or if the car is supercharged or not. These are the questions that you will need to answer when looking to find the correct factory cats. Oh, you want them installed, that is an additional cost.

I'm sure about now you are in sticker shock. You can install aftermarket cats. That will be a lot cheaper and you can probably replace all 4 cats with good aftermarket ones for around $800 or so. Talk with the muffler shop and see what they say. Essentially what they are going to do is punch small holes in the exhaust system and see where there is lots of pressure and where there isn't. From there, they will have a good idea of what is bad and what isn't. They will probably also tap on the cats and see which one(s) is/are rattling.

As for the lambda sensor, it isn't a stand alone sensor per se. What it simply is is your upstream and downstream O2 sensors and the computer is comparing the oxygen levels between the upstream and downstream gases of the cats. It is looking for a difference in the oxygen levels, which is indicative of the cat burning the CO and unburnt hydrocarbons. if you want me to go deeper into this, I will. But this is a simple explanation of what that system does.

 

thank for your reply.
I have a v8 4.0lt xj8.

I fully understand your reply interms of how many cats are on the system and the job the sensors do

My only concern is that if the 02 sensor is faulty due to the age and milage of the car, then the first test should be on the sensor.

I have a feeling that during the recent AT change the sensor has been damaged and since that time the MPG has gone down form 19MPG to 14.5MPG in town and 28MPG to 19MPG on Highways.

What i cant understand is why is there no engine management lights on my dash???.

I have prepared for worst, i.e a fully system change at £1.0k.

 

jagman, you can have a tech put the car on a scanner and based on the different voltages that he sees there, he can determine if you have a bad O2 sensor or not. But, I am leaning towards the bad cat due to the rattle that you have from under the car. Granted, since you will be taking the car into a shop to have them do the exhaust for you, have them do a quick look at the O2 sensors. It will be worth a look and could save you a lot of money. Odds are, if they are bad, it will be obvious since the wires will be damaged.

Good news for you, your motor has some of the cheapest cats, so, that should make your wallet happy.

 

Thank you for all your help.

Will let you know the out come. My local independent Jag garage will test the car next thursday.

 

we'll be crossing our fingers for ya!

 

I believe the XJ8 has two converters, one immediately aft of each exhaust manifold.

 

would a collasped muffler cause problems with the emissions test.

The two before the back box have splits on the joints. I did a temp repair with a hardening compond, but not too sure if they hav collasped internally.

 

What is the warranty on cats? I thought these were warrantied by the feds because it is government required? I thought it would be paid for by them, so check it out before you shell out a ton of $$$ to replace them.

 

I dont think there is any such undertaking by English law.

I will dig around to see whats what.

Thanks for the advice

 

Here in the states thats the law. I would assume it would be the same in other countries too if the gov. required emissions on cars.

 

Thanks for all the help and advice.

Turned out to be the oxgyne sensor on the down pipe.
On the re test the co is at 0.01.

Also treated the Cat with some high tech cleaning fluid and now drives like a dream.