The lftf is supposed to be a long average. And from my reading influences the base fuel bias.
so in theory it will move down in time.

 

I am not aware of any information that says the LTFT affects fuelling in any way. It is simply a long term average of the STFT readings that is useful in diagnosing fuelling problems. The PDU allows me to reset the LTFT. It does absolutely nothing, except reset the long term average to see if something I may have done to the engine has changed the fuelling.

If you have seen any other info, please share.

As for the 02 orientation, that is a simple reset that allows the car to figure out which 02 sensor is located where. If the 02 sensors are incorrectly plugged in, the engine will run miserably. Instead of figuring out where the mistake was made, the 02 reorientation is a Jag Dealer's quick fix. There is nothing to confuse or relearn. If the 02 plug is plugged back into the wrong harness, its just wrong and needs to be fixed. No amount of time or driving will let the engine relearn anything, either figure out the correct plugs, or run the reorientation.

 

Vee is correct on both counts. LTFT is not an input to the ECU, it is an output and represents ta the average of the STFT.
Also, the car can’t self learn its way around the O2 sensors being transposed.

 

Cool cool.
i had not read anything specific to this car regarding ltft.
just general reading.

would still be good to reset it to see where the average sits now after all my work.

will record the stft again whilst driving.
From what i gather from what people have said, the stft should move but remain closer to 0 than what mine are.
not sure if mine show correct, if the device is off or what.
maybe its just exhaust leaks causing it now.
that would make perfect sense.
but, since changing the injectors i know that the car runs better. I have no petrol smell from exhaust anymore so that is a huge plus!!!!!
happy with how she purrs atm!

i f
don’t think the o2 sensors are wrong. Car runs too nice compared to how i heard it would.
the wire colours match the banks as they should.

 

Hey Spud and others,

Have a look at this thread below and you'll find a good discussion re fuel trims and in post #29 there are two linked articles with a lot of useful info.

Cheers,
Jeff.

https://www.jaguarforums.com/forum/g...ed-quiz-49317/

 

jeez thanks for that. Lots to try to read and understand.
interesting that potentially a k&n filter can have impact.
i have one of those might be interesting to swap to normal and see if a difference


i know there is no point trying to get the ft correct whilst i have exhaust manifold crack but its interesting to learn.

anyways here is a sample of where i am at now.
far better after the injector swap

 

Spudmat, you have just introduced another topic, K & N Filters -

Seems you are keen on reading, here is some more, K&N Response to Mass Air Flow Sensor Concerns, plus heaps more on google etc.
All I can offer is that I have used K & N filters in all my cars (including several daily drivers, not Jags) for more than 20 yrs & am unable to lay blame on them for any problem.
Misinformation, there is just so much out there -

John Herbert
1996 XJR

 

you are 100% correct. misinformation is everywhere.
sometimes spread by corporations,
sometimes spread by people who just repeat what some bloke at the pub told them.

i am always keen to look, read, and try and actually find out what is the case.

 

on the note of LTFT tho i think for certain my fuel injector O-rings were shot.
i previously had a LTFT on both banks of +10.2
after i di my injectors my LTFT is now +9.4
so whilst it still indicates too much air in the exhaust it is better than it was by 0.8%.
which indicates to me that air was sneaking in past the injector seals.

 

I understand your logic on too much air going into top of cylinder ( s ) and in a closed loop the O2 sensors will try to bring the 1 back in mixture line ( as a group of 3 as 1 bank or all 6 )

If only 1 cylinder getting too much air the ECU will bring in too much fuel to all cylinders in a group

But unlikely that you're getting too much air in my opinion and better to resolve manifold leak

It is a tight fit getting injectors with O - rings into heads and assembly lube ( Vaseline or just petrol ) helps , inspect for cut O - rings as being scalped going in last

 

Yeah. Exactly why i said i think there “was” a leak at injectors. Since changing them my long term FT has dropped.
so happy there.

and yeah no point trying to chase anything when the exhaust manifold is cracked.
there may or may not be something else but hard to find B or C when A is a problem.
too bad there is no quick easy way to fix the manifold.
PITA job.

 

Given the LTFT is steady at the same number and never fluctuates i am guessing at this point it is ALL caused by exhaust manifold cracks.
i would
suspect that if it was any pre-combustion leak it would get better at higher rpm. As more fuel gets dumped in it would become a lower percentage of excess oxygen.
however in the exhaust it is always the same amount of excess oxygen.
(Thats what my research leads me to believe)

 

I also have exhaust manifold cracks. I have seen my LTFT at 0. I, personally don’t believe that’s the problem.

The LTFT does not go back to zero instantaneously once a fix has been installed. It takes time, so you’ll see it slowly go down as the average works its way back closer to 0.

 

i understand it does not go back instantaneously but from everything i have seen looking at videos you can actually see fluctuations whilst the car is idling it is fairly quick.
i have run the car now for hundreds of KMs.
just yesterday it actually went back to 10.2
the great little PDF that was linked here indicates it should change in 6-8 mins

everything i can find about LTFT online (aside from what was posted here) is all general info not car specific and also indicates it changes base fuel map.
reading other stuff and watching other videos, implies that 10.2 means the car is showing a lean running history and is compensating by adding 10.2% extra time to injector pulses adding extra fuel. here i have been told it does not work like that.
so trying to decipher exactly how it works and learn is a long process.

i am going to buy a little smoke machine and check for vacuum leaks.
not that i think there is any but good to know and rule things out.

 

My responses in bold. The smoke machine is a good idea. I tried using cigars and while it does a good job, I was unable to find an intake manifold leak with it...I suspect I needed far more pressure than my lungs would allow. But any other leak source should easily be found with a cigar and some lungwork.

 

Well what i have experienced is Inhad thesame checked the o2 sensors and cleaned on one bank I had als misfires during a cold engine and a irregular running so I had a litre wynns 7 in 1 cleaner put in my tank and since then it's running like a charm after a cold start

 

Maybe time to look into EVAP vacuum system and vacuum leak from an open Rochester valve near main fuel filter

You can take a 9 volt battery and test the EVAP valve ( left side under air filter / bonnet ) by clicking sound and blowing into hose if open or closed

If you have a Rochester valve by fuel filter by the time you set up a test , easier to just replace it

Someone did find his Rochester plumbed in backwards

Have you determined if you have the 1 or 2 square vapor canister EVAP system ? 1 canister does have a vacuum controlled Rochestor valve , 2 canister does not replaced by a electro valve ( canister close valve )

And still get around to cracked manifolds if resolved

leak on oil fill cap ? Fuel fill cap ? When removing fuel cap a whooshing sound ?

Took me some time to square in my head the green fuel trim chart until I added the extra notation of what the ECU commands to corrrect/ move to get back to target 0

I found on mine the vacuum hose from under the intake manifold ( about cylinder 2 ) to the EVAP valve nearby totally missing thereby leak . but I had a - 25.4 % fuel trim reading which is the limit of the reader device ( pius a cracked exhaust manifold )

As Vee suggested the small run vacuum hose for the FPR and a blow test into hose that the diaphragm is not leaking

Even a small leak in the FPR ( if detectable ) would have a huge effect on fuel trim ( fuel flow through hose to intake / rich ) and long term fuel trim , this also effects if the injectors fuel pressure is not brought down from the higher fuel pump itself supplied pressure

I always wondered if the stainless steel square vapor canister was to rust out and leak ? fuel tank sealer repair

Is a solution to the EVAP system just to cap off the vacuum line under and attached to the intake manifold ?

Eventually you do not want the fuel pump to draw down and collapse the fuel tank , seen that before on an aircraft as it does happen

See page 60

jagrepair.com/images/Training Guides/801S - 2000.pdf

 

re a previous post "I am not aware of any information that says the LTFT affects fuelling in any way. It is simply a long term average of the STFT readings that is useful in diagnosing fuelling problems."

This is completely inaccurate as both are used to calculate fuel delivery. As an analogy, think of the LTFT as course tuning and STFT as fine tuning. Fuel delivery is then calculated as Base Fuel + (A * LTFT) + (B * STFT) where A > B and each fuel trim can either be positive or negative.

LTFT is incremented (decremented) if the STFT exceeds a positive (negative) limit in either magnitude or time. Ideally, one wants to see the STFT bounce around zero.

 

Sounds like an opinion, or a theory. Have you ever read anything that backs up your hypothesis, or are you just making an assumption based on other vehicles and engines?

Please do not push unfounded theories as fact. There are people here that still believe there is a "hard reset" for the AJ16 ECU because people "heard that it works".

 

I used to write the code for engine controllers (spark, fuel, etc). Not tune, I wrote the actual code that the ECM's used to control the engine. Cars, man lifts, marine, generators. Been there, done that. All EPA certified. It has been awhile, but I know of what I preach. There may be a hard reset, I do not doubt that. I am simply explaining how LTFT and STFT work. What I said is fact.