Ok so as some of you know I thought I had a MPG/Emission problem as per my previous posts, I replaced my exhaust as a first port of call as it had 8 holes in it and wouldnt help the situation.

I have now had my MOT done and attached is a copy of the emission print out, the car passed but he said he had to get it warm and play around with the RPM to get it through.

Can you take a look at the figures for me to see if its ok feuling/O2 wise.
The MOT bloke said my O2 senors are ok, no fault codes, but my cats are the orginals and now the car has done 155k nearly they take longer to heat up hense poor MPG round town, on a long run this would be normal though.

Does all this add up in your opion?

 

That's actually a very good MOT emissions result & pass. The Lambda value is right in the middle of the limits & the CO/HC level is very low.

It's normal to make sure the engine & catalysts are fully warmed-up for the emissions test anyway.

In the winter months a car will use more fuel as the engine warm-up cycle is starting from a lower temperature point, and the viscous drag from the cold engine oil, gearbox oil, differential oil & wheel bearings will all increase fuel consumption in cold weather.

These cars are fitted with 4 O2 sensors, so they will monitor the quality of the exhaust gasses after the catalyst as well to keep an eye on catalyst efficiency. If the catalyst efficiency starts to deteriorate then it should flag up a fault code.

You can improve catalyst efficiency by taking the car for a long motorway cruise. This type of driving puts the system in 'closed loop' mode & keeps the air/fuel ratio around the Stochiometric value which allows the catalyst to work.

Hard acceleration & variable-speed/acceleration driving styles cause the ECU to go into 'open-loop' mode & the air/fuel ratio goes outside of the Stochiometric limits (usually richer) to give good acceleration.

To 'clean up' the catalysts, you have to drive the car in a style that forces the ECU to adopt the 'closed loop' fuelling pattern & keep the air/fuel ratio at the level the catalyst requires to work at maximum efficiency.

This can be easily done by going for a long motorway cruise at a steady speed, without any hard acceleration-just cruise along at around 60-70mph for 50-100 miles so the catalysts are working & have chance to warm up fully, which often burns off the softer carbon deposits on them & improves catalyst efficiency.

 

Great thanks for your help again Red October, I may replace these old cats in the future as it would make sense now I have a custom exhaust system fitted and I may gain some more power which isnt a bad thing. However Im driving down to spain soon so 2000 miles of 60/70mph should give it a good clean out.

I hardly ever use the car and before its MOT it had stood for 3 weeks in a garage and done a short 2 mile trip to the MOT station so this will be why the CATs where playing up a bit for him?

Thankfully it appears I wont be changing my upstream O2's anytime soon so happy days.

Thanks again for all your advice, its been spot on and something you cant get at your average garage.

 

Happy to help & yes, the short 2 mile trip to the garage for the MOT will be the reason that the tester had to fully warm-up the catalysts. I always warm up any petrol car before an MOT emissions test-I make sure the temp gauge is in the centre with a warmed up engine & then drive the car hard for a few miles before the MOT.

The catalysts don't work all the time anyway-only in certain engine 'modes' such as idling & steady-speed cruising. Under these circumstances the air/fuel ratio is kept at the 14.7:1 Stochiometric level & the system will be in 'closed loop' mode & the catalysts will be working.

So the best thing you can do for the the catalysts & also the O2 sensors is to go for a long steady cruise, as this will put the system in 'closed loop' mode, which will make sure the catalysts are forced to work & heat up properly.

A good steady drive down to Spain will be the ideal type of trip to really heat up & clean the catalysts & O2 sensors-just what these cars need

Most MOT emissions failures in the UK are due to the car being driven around on a cold engine for short journeys. The catalysts & O2 sensors never really get hot enough to work efficiently & they 'soot up' with soft carbon much more quickly.

Quite often all that is needed is a long steady drive to get everything really hot & burn off the soft carbon...

Anyway, good result on your MOT & another Big Cat kept on the road for another 12 months

 

Sorry to bump this thread again but still having issues in this department.
Had my local garage do an emission test this morning and all three tests are way way out in the red, CO, HC and Lambda, CO giving a reading of over 9000.

Now I always thought the issue was my 155k Cats which I have now had replaced which a pair of sports cats (200 cell) which the exhaust man said would pass an emission test with no problems, is this true?
I have no error codes or lights on the dash, I'm wondering if it could be an upstream/upper lamba sensor thats has near enough packed up as I also have a lot black soot on the left exhaust section, which is probably due to running to rich.
Help!!

 

Dead lambda sensor doesn't always give a fault code - didn't on mine.

Was found by posting the fuel trims on here so get them and post them up, should tell you if the lambda sensors are good or not and which.

 

What can I use to get the fuel trims?

Also I think Ive read on here you can use lambda sensors off an xtype for the upstream for a fraction of the cost?

 

Do you have an obd reader?
If not, the following page gives a list of readers that will work with the X308.
They can be had for less than $100 off ebay, and are essential for maintaining this car.

https://www.jaguarforums.com/forum/g...oved-**-33347/

 

Ok thanks, do I just make a note of the fuel trims at idle or specific RPM?