It's a 2 sensor car not 4, just by a pair of O2 sensors. The X type fit on these cars, but can't recall if it's for AJ26 or 27 engines (white and grey pairs of connectors, and only the grey pre cat O2's??) only cheaper 2nd hand but more readily available, they wear out like sparkplugs. I don't recommend non oem and splicing the connector, but I always use oem

Did you have the cats replaced with non oem units, might need cheaters installed on the O2 bosses, ecm thinking it's running lean and dumping fuel in, i.e. O2 sensors getting too hot as they're to near the exhaust gases?

hope this helps.

 

I had sports cats installed so none oem, I believe they might have been the sports cats for the x350 xjr.
What are cheaters? And where can I get some?

 

Look for a vacuum leak- Most likely a hard to see split along the full load breather tube.

I do not understand your original post though- You day it is running lean but has black ssoty smoke, which is generally a sign of running rich!

 

My mistake its running rich

 

Ok, then, your ful trims are high even though it is running rich, so that definitely points to a bad sensor. They are commanding more fuel when it is not needed.

 

Quick bump and update.
Testing pointed to a dead lambda on bank 1 upstream sensor, replaced it and MPG has gone back to where it was before my exhaust work. Hitting about 29-31mpg @ 50mph, still not great but better than the 12mpg I was getting, plus the car has done a few miles.

However I then tested the fuel trims again and I got the same reading as before, both banks ST and LT trims where both stuck at +14 and +19 not moving at all. Any ideas why this would be. Even the 2k garage ECU reader showed the same results.

 

Great post

 

Wrong place?

 

Bump

 

Hard boot time? Have you examined the Full and part load breather tubes CAREFULLY?

 

All breathers have been checked and double checked, however if the trims are showing +Positive doesn't this normally indicate the car is running rich therefore pointing to a Lambda.


What's a hard boot? If your referring to resetting the ECU, I tried that this morning and re-tested again. For a short time the LTFT's on both banks did come in correct,(STFT still high and constant), but after a couple of mins they went back up and got stuck there again.


Pulling my hair out with this now.

 

No! First, the fuel trims do not tell you if the car is running rich or lean- They tell you how the car has corrected to what it THINKS the car is doing. So, positive fuel trims mean the ECU is told to increase the amount of fuel injected to compensate for what is detected as a lean condition. Hence my original post that if the fuel trims were positive, AND you were running rich (detected by the exhaust), that would indicate a bad sensor. Now, your sensors are detecting lean, and adjusting the engine towards rich. Do you have any reason to believe the engine is not running lean?

So, I would say the next thing to do would be to carefully clean the MAF sensor with MAF cleaner. If you are not sure on how to do this, there are posts in the archives that describe it better than I can write, but be careful to not actually touch the sense wire itself! The rationale here is that the MAF sensor MIGHT be reading lower airflow than is actually the case and the lambdas trying to have the ECU compensate. They can, of course, only compensate to a certain point, and not across the board for all conditions.

For a good explanation of fuel trim, look here: https://www.jaguarforums.com/forum/g...ed-quiz-49317/
Thanks to Steve for this excellent write up! (Post #3 on the thread)

 

Thanks for the post, I cleaned the MAF senor around a year ago, at the same time as replacing my K&N panel filter, worth cleaning it again you reckon?

 

Ohhh- The oil used on an aftermarket air filter has been reported to screw with the MAF. I do not have any experience with them myself, but several times I have seen folks say they were going back to original.
BTW, I added a link in my post above post- check it out

 

Going out to clean MAF with MAF Cleaner now, BRB

 

Done that, still no change :-(

 

If you do a hard reset, like it sounds like you did, the LTFT should go to zero, and it sounds like they did, and they went back up, then you've either got a vacuum leak, or faulty fuel pump, fuel filter or injectors. Many people, me included have had vacuum leaks around the intake manifold seals. Or another popular candidate is a leak in the part load breather hose. I assume you already checked the intake plumbing and "resonator" tube off the intake trunking. Can you get a smoke test ?

 

Correct hard re-set and they went back up. Just been out again and checked the intake resonators and they are on nice and solid, checked part load and full load breather hoses again nice and solid. Fuel filter was replaced around 2 years ago, and I have no other running problems to suggest a faulty pump or injectors. Everything also seems ok around the throttle body where the intake and rubber seals meet.


While I was testing I did notice however when I removed the part and full load breather hoses it made no difference to the fuel trims at all, yes the engine completely changed and became rough but no change at all in the trims, could this mean anything.

 

Your fuel trims are probably "pegged", meaning they have gone as far as they can and more air just won't affect them. It is pretty sure that you have a lot of unmetered air gettinginto the mixture. Whether than is from the MAF not reading it, or the air getting in another way, it is hard to believe it is anything else.

If you are not convinced, then you could try some of the following techniques- Have someone test the exhaust stream to prove the exhaust is either lean or stoichiometric- It MIGHT be "right on" in that + total 30% fuel you are putting in might be the right amount for idle. You could also let some propane from an unlit torch into the intake air stream to richen the mixture. At that point, the trims should fall and the engine might idle smoother.
You could also block off both breathers (block the side towards the induction) and watch the trims. That would tell you if the leak was into the crankcase.

 

Would a dead maf sensor through up a code? Wondering if its worth replacing it....