The fuel trim readings have a permissible deviation between them before the ecu gets really upset, and yours is within this deviation, but it can still be a reliable early indicator of a problem.

Usually the deviation is to compensate for manufacturing tolerances in the injector, and/or engine wear, but it can also alert you to a fuelling issue.

Tesla

 

It's a better idea than any I still have!

 

JagV8 You have been of great help to me on many, many occasions!

 

I hope to have been helpful - many others helped me in the past so it's time I did my bit.

 

Well (fingers crossed) I cleaned and swopped injectors on 2 & 4 and my intermittent DTC's P0302 & P1314/6 appear to have gone away! After 6 DTC-free cycles, would it be overly pessimistic of me to expect them to return?
However, I now have a Component Failure! (please see following pics):
Any ideas what I should look at next, please?

 

It sounds hopeful - mostly!

You may be suffering as in this PDF

 

Hello JagV8. Thank you - I do believe you have this right.
I obviously disconnected my battery before switching out the injectors. This error was not present before I did so and (because I have also been draining down and flushing my coolant) I have only had 2 or 3 short drive cycles since - And all of those with a full fuel tank.....

 

JagV8 - You were spot on. My fuel level dropped, the Evaporative Leak Test obviously completed and my Components have now passed their test!

In conclusion, my random misfires on number 2 were being caused by a clogged (or leaking) fuel injector; all DTC's have been clear for several driving cycles!!

 

Feels good, doesn't it?
Sweet taste when the problem is solved.
The harder to vanquish, the sweeter the victory!

 

You are SO right!

 

Heyyy- good to hear!

 

I am still puzzled by my fuel trims. About a million years ago, JagV8 kindly sent me a Fuel Trims Primer and I thought I understood (well, pretty nearly, anyway) how they worked?
However, I do not get the consistent double-negative of my bank 2 trims? Surely, if the short term trim is consistently taking fuel away, the long trim should not be consistently doing the same? Could this be indicative of a leaking injector? Perhaps the injector that was causing my misfires on cylinder 2 and I swopped out (and cleaned as best I could) to 4 is now leaking in cylinder 4, but not in such a way as to cause a misfire code?
I suppose this could also be that my trims simply need more time to settle down after much being played with?

Fuel Trims 03 Oct 18 - No DTC's

 

An update on this post in case it could help someone.
While I had my Inlet Manifold off the car complete with Injector Rail (Michael Hamilton EGR Valley Hoses NON S/C post: https://www.jaguarforums.com/forum/x...on-s-c-149873/) I decided to have all 8 of my Injectors cleaned and tested. The garage rang me this morning and (as I and several of the forum members who generously assisted me suspected) the injector at cylinder number 2 (swopped out to 4 for checking) was blocked! Interestingly, this blockage was causing a misfire on number 2 which did not transfer to number 4 after the swop? Maybe the BG44 I added to my tank was providing a temporary solution? Anyhow, well done to Tesla (post #21) for hitting the proverbial nail on the head!
I will post what effect (if any) this unblocked injector has on my fuel trims!

 

Hello Tesla and JagV8, Apologies for disturbing you. You both gave me helpful replies to my Replacement Fuel Injectors post regarding my Fuel Trims. I have had all my Injectors cleaned professionally and (as we suspected) Injector number two was blocked and dribbling! My car is now running beautifully, but I still have a slightly strange Bank 2 Trim and I find negative trims harder to diagnose so I would very much welcome your comments? Please see below:

 

Your bank 1 fuel trims look great. The bank 2 fuel trims (-3.5 LT and -4.6 ST) indicate a slightly rich condition. The total trim is -8.5%, which means the PCM is reducing the injector pulses to lean out the mixture. As mentioned by others, you are well within the limits of setting a rich code (usually it's 25% in either direction), however if you're near 10% you might consider looking for causes of the rich or lean condition.

With regard to the -3.5 and -4.6 trims on bank 2, this is typical of these Jaguar adaptations. On other vehicles, the PCM's goal is to adjust the LT trim so that the ST trim stays around 0%. So in your example, it would reduce the LT trim another 4% to a -7% trim, then the ST would be hovering around 0%. Same total trim, different strategy. I'm not sure exactly what adaptation strategy the Jag uses, but I wouldn't be concerned about seeing two negative numbers (or two positive numbers).

All that said, I'd drive it a few hundred miles and see where the trims end up. What you'll want to do is take ST and LT readings at idle, and also at 2k rpm. If you take them while driving, they will be constantly changing due to engine load conditions and never make sense.

 

Understood, Michael - Thank you.
Just to clarify - My Bank 2 STFT is -0.78 and my Bank 2 LTFT is -7.03 - Am I reading this correctly? Or am I (probably) over-reading this?

Incidentally, there is still no sign of the Suspension Fault or of its consequences since my battery charge and hard reset! https://www.jaguarforums.com/forum/s...d.php?t=211032
(My apologies for crediting Don with your post)!