Cheers!

I failed emissions today but luckily (?) it is only Lambda-value which is high.


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While XJR was in the air and idling we could feel by hand one of the exhaust joints after center muffler leaking. Would that be enough to cause high Lambda-value?

This car had last year full cylinder head repair because of leaking head gaskest so I do not think the leak would be there.

Apart from this exhaust leak what other reasons would you suggest?

PS. Forgot to add: there are no ill symptoms ie. steady idle, good power, good MPG, no warning lights.

 

When I had a high Lambda on my NA car, it was the O2 sensors that needed replacing. From memory though various measurements were out of allowed range, so your issue might be something completely different. Not a lot of help I know, but a bit of info. I'm sure far more knowledgeable folk than me will point you in the right direction.

 

A leak after the center muffler ( or the rear Cat in some areas ) will have no effect as this is aft of the sensors . The sensors can be remove and soaked in gasoline ( getting into the slots where the area of interest is ) and maybe refreshed . Clean the sensor connector of possible corrosion and clean the sensor wires shielded ground ( nevermind it grounds back into the ECU as the dashed lines ) . Don't cross the sensor connections

Other then that the sensors don't last forever .

A coolant leak at the head gasket into the cylinders will foul a O2 sensor and I'm not aware if it can be cleaned or refreshed

Bosch probably has a cheaper connector ready equivalent sensor then the presumed OEM Denso brand . Upstream sensors may have a different wire length to them compared to the downstream

 

Sorry but I failed to mention that this measured Lambda value of 1.08 is not a value from any of the car's own lambda sensors but a measured one from exhaust outlet end with a sniffer pipe to analyzer called PKA3.

 

the leak shouldn't effect the test equipment sensor , just a smaller sample size . I would target the bank you had the head gasket change on if replacing sensors , otherwise clean electrical connections and verify proper connection positions . Depends if they charge you for retest

 

You can look at each bank using OBD and see what the car thinks. Usually you'll get useful clues.

(Have a good look at all the relevant live data.)

 

Leaks were repaired and emissions re-tested again today - no improvement.
I think I need to go to Jaguar service and have them look at it with their computers. Could be some sensor, Lambda or some other, malfunctioning.

 

I think the guys are onto it in that it's likely to be an O2 sensor issue, that is if the engine is behaving correctly after the head rebuild - which it is by your information.

Another thing to look at are Fuel Trims via OBD - report what you have here

Also give the MAF sensor a clean and then carry out a hard reset, let the car idle for 10 minutes after reset restart to allow the car to load its base fuel and throttle maps. Then see how it tests.

 

Thanks, Sean.

Out of curiosity, what brand are the original O2 sensors?

Brisitshparts.co.uk seem to have fairly decent prices for the sensors.

 

Well, today we
- cleaned MAF (had silvery residue)
- cleaned throttlebody (had black gunk)
- checked part load breather (was clear)
- reset the computer

I'm having this re-tested tomorrow. If it still doesn't pass I will consider replacing all four O2 sensors.

 

As a follow-up:

It turned out that heating circuit of the right upper oxygen sensor was faulty causing this problem.

Sensor was changed today at Jaguar dealer and emissions re-test was OK so it now passed the yearly MOT. Which is nice.

It feels like the engine runs smoother and MPG appears to be better by 5...10% - computer is probably still learning.