@bladerunner919, I asked that question of the MOT tester, apparently the exhaust gases are combined at the tail pipe.

 

So presumably the overall lambda at the tailpipe matched what the sensors were reporting. BTW you need to look at the upstream sensors, not the downstream. Your figures show the car thinks bank 1 is lean and is adding fuel. You would expect to see that reflected in the upstream O2 sensor for that bank.

 

Assuming a UK car, as the OP is talking about an MOT test, it won't have downstream sensors.

I'm still not clear on how the sensors have been categorically ruled out.

 

I thought all X100s had downstream sensors?

I think the OP needs to go back to his indie and ask how he determined the upstream O2 sensors are both working. The car is adding a lot of fuel which suggests the sensor is reading lean - why did the mechanic think the sensor is ok. It seems a big leap to say "try a new engine" rather than "try a new sensor".

 

Mine doesn't & the cats just have blanked bosses where they would fit.
I'm not sure if that was the spec for UK/EU cars with the AJ26 motor?

I *think* they became standard when the AJ27 was introduced.

 

I didn't know that. Looking at the electrical guide for the AJ26 it does show two different versions of the engine management, one for NAS and the other for ROW. Only NAS has the downstream sensors. For the AJ27 there is only one version (with the downstream sensors). Presumably this is part of the reason my 2001 XKR is ULEZ compliant if I ever drove it in London (meeting the Euro 4 specs 4 years early) when the earlier cars weren't. I always liked the idea of buying a 20+ year old 4 Litre supercharged Jaguar to avoid the ULEZ charge.

 

To reiterate what others have said, my 1998 does not have post-cat sensors.

I agree that OP needs to go back to the mechanic - no part of the diagnosis makes sense to me. My guess is that this was an O2 sensor problem all along, and replacing the cats with new ones did just enough to get the fault car through the emissions test, whilst not actually addressing the cause. To be perfectly honest, I think the OP needs a different mechanic that can actually do diagnosis rather than just firing the parts cannon.

 

Hi RichSP,

I've been reading your thread with great interest. One point we can clarify is that if the numbers you posted are correct, the fuel trims indicate that Bank 1 is running LEAN, not rich, unless you meant to put negative signs (-) before the STFT and LTFT numbers... As shown, the data indicate that the ECM is increasing the Bank 1 fuel injector pulse durations in an attempt to maintain the ideal air-fuel ratio (AFR) because the upstream O2S is reporting excessive oxygen in the exhaust.

The most common cause of lean running is unmetered air leaking into the engine somewhere past the Mass Air Flow Sensor. In your case, the air leak would be somewhere that affects only Bank 1, which is the right hand bank as viewed from the driver's seat.

One common leak point is the full-load crankcase breather hose/breather restrictor, the corrugated black plastic hose that connects to the Bank 1 camshaft cover to the main air intake pipe.

Other contributors could be a leaking camshaft cover gasket, spark plug tube gaskets or the VVT solenoid gasket. If you can see oil seeping out, unmetered air will be inhaled under engine vacuum.

Another common cause of lean running in only one bank is a leak at the exhaust manifold gasket or a cracked manifold. As the exhaust gasses pass through the manifold, outside air is drawn in via the venturi effect. Are there any noises on the right side of the engine that might suggest an exhaust leak? Could there be a leak where the new cat connects to the exhaust manifold?

Another common cause of lean running in only one bank is one or more obstructed fuel injectors.

To rule out a problem with your upstream O2S's, you could swap them and see if the lean running moves to Bank 2.

I'll be watching your progress with great interest.

Cheers,

Don

 

Hi All. Thanks to everyone for their advice and support. I can report that, as a result of a trip to Swallows Jaguar the problem is now fixed. The cats have two O2 sensors and Swallows trial fitted used sensors on bank 1 - emissions now fine. The sensors are the most likely reason why I had to replace the cats last year.
This is soooo frustrating as I asked the original Jag indie if the sensors could be the problem, but I was given a **** and bull story about possible VVT issues, dead cats, worn timing chains and Nicasil failure being possible culprits. Recommendation? Source a replacement engine and we can fit it for you. I'm drafting a stiff letter as we speak!
Still, I've learned a lot in the course of this thread, which I'll be following up in more detail. The biggest take-away is to check the O2 sensors before assuming that a cat is bad.

 

Glad you sorted it, but a shame you had to go around the houses to get there. There are too many so-called mechanics that are nothing of the sort - they are just fitters, with no diagnostic ability, whose answer to problems is firing the parts cannon until they get a 'fix'.

 

Yes, but a replacement engine is one of the biggest loads the parts cannon can fire!

any so-called mechanic/technician who either, can’t or won’t do proper diagnostics is no mechanic in my book…yes- just a parts changer!

Brian W.
2003 4.2 XK8 conv. normally aspirated, serial A35010, 77,000 miles