www.jec.org.uk

HI,

Does anyone know what is the most probable cause of high emissons on a V12. My car is a 6.0ltr and only just passed the MOT emissions test as it was on the border mark.

Both sides are high with one being on the MOT limit. The engine runs fine although tickover can be a little lumpy sometimes. The car is now 12 years old and only does short runs to car shows etc. Would it be advisable to get the fuel injectors cleaned and possibly change the oxygen sensors? I beleive the oxygen sensors have only a life of about 6 years and then start to deteriorate, which can then enrich the fuel.

Fuel economy according to the computer is an average of 19mpg and on a steady run 23mpg. Performance is also good. The car is serviced by a Jaguar specialist every year and has only done 78,000 miles.

Hi,

I have just experienced the same problem with my own 6 ltr, mine is a 92 with 84k on the clock.

The MOT station did a full CAT check on both banks which took over 15 mins each before the analyser managed to get the amount of Co2 that was needed to complete the test. (that is what the tester quoted)

It was border line and the garage informed me that it was probably the catalytic converters that were probably shot. my model had two fitted (XJRS with Zytec ignition system)

Not being of a high tech nature I doubted this and sought further advice. A very helpful Jaguar performance specialist informed me that even with the CATs shot and subsequently removed it should still pass the emmission test.

He suggested the fault could well lie with the Lambda sensors or fouled injectors as you suggested.These would have to be cleaned ultrasonically.

Also the distributor cap, rotor and coil tower could be worth checking as a slight misfire could lead to a high co2 reading.

In the end I had it put on another analyser at my local independant specialist who declared it well within limits!

Not much help I'm afraid but I suppose it is good to share these types of experiences.

All the best

Hi Alan,

Thanks for your reply. I agree with your specialist and that it won't be the cats on either of our cars. Over the winter I am going to get the injectors sonically cleaned and probably change the lamda sensors. I have also recently found out that if the external air temperature sensor for the engine starts to fail, this will make the fuel 10% richer going into the cylinders which of course will give much higher emmissions.

Regards
Steve

Hi, My dad has an x300 4 ltr 6 cyl and had the probs with emissions. Had the lamda sensors changed and this cured the problem. That was his starting point and cheapest option which worked well. It also improved his mpg. Dawn

Lambda sensors are prone to failure - I had one fail on a 95 4.0 AJ16 this year. However, it's quite practical to definitively check them with a voltage sensor. You can do this yourself or a dealer will do it for free particularly if they think they'll get the repair work!

I would definitely confirm that there is a lambda sensor problem before replacing them. I don't really agree that they are the cheapest part of the problem. The prices vary hugely - Jaguar charge circa £230 plus vat each for them. But you can buy original NTK 4-wire titanium ones for circa £70 privately. 3-wire sensors, which are probably the ones fitted to your vehicle can be bought cheaper. Hope this helps.

Thanks to you all for your helpful replies. It is good that we can share in each others problems and give advice to each other over this bulleten board.

Regards
Steve

Steve et al - I have a similar problem on my 89 6.0. High CO in my case, probably related to overfueling (see my other emails elsewhere). It's hard to get definitive information as the Jaguar manuals are all over the place. But from what I've read and concluded, the external temp sensor (2 on an XJRS, in the air intake bellmouths) are less important than the temp sensor (nearside water rail). If this fails, definite overfueling takes place. The Jag XJRS CD ROM confirms this. The air temp sensors are much more of a 'trimming' device.

In my case the car is definitely using too much gas - 2mpg instantaneous at one point! I've turned the trip computer off now so my wife doesn't see it...

this may be a bit after the event but I went through a major trial trying to get my 93 6.0ltr through the MOT after fitting an AJ6 TT exhaust system which involved removing the cats.
the only part of the CO test she failed on was the idle test, she passed on the other two. We were only just off the pace. After about £ 750 of testing which included cleaning all the injectors, the results were no different, suggests that when the engine is in good shape it can almost do without the cats and that's after 89 000 miles!
However, in ordre to get the car through the MOT I had to put the cats back on and leave the TT system in the garage for another day.
I don't know if anyone else has any experience of trying to fit a TT system and have they been successful?
If anyone wants one then give me a shout, my one has done only about 1000 miles with 1 careful owner!