I've noticed that my high LTFT reading appear as soon as the Torque app connects to my ECU, even before the engine has started. Is this normal or it it doing this because of the way its been remapped for the +10% supercharger pulley, 200 cell cats etc?

 

Sounds like just junk data? LTFT's have no meaning if the engine is not running? How can the system measure anything if nothing is operating?
LTFT is just a measurement of the current operating conditions. It does not know anything about the car and if it's tuned or not.

Kind of like your speedometer. It reads the speed regardless if you have a 100HP Diesel or a 600+HP super charged V-8 under the hood.
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The STFT is live data, the LTFT is learned over time. Not the same thing.

 

The ECM keeps the learned LTFT in memory assuming it will need to be running at that value when next started. It corrects from that value if it sees it is required.

 

Thanks, that's what I thought. Just wasn't sure if maybe the map was taking the LTFT and incrementing it by a fixed amount due to the +10% pulley and 200 cell cats etc.

 

Except the LTFT also use the STFT in the calculation and if the car is not running won't that affect how the LTFT are calculated?
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No. Because the STFT is an almost instantaneous that changes by the second. It is invalid in the next second. It corrects for acceleration, hills, throttle release etc.

 

This says that the STFT do in fact play a role in the LTFT calculations?
How is LTFT Calculated?

Here is their exact statement;
There are two types of fuel trim – short term (STFT) and long term (LTFT). STFT is used for immediate adjustments based on the parameters, whereas the LTFT is a slower adjustment. The LTFT value is stored in memory and "learns" from the STFT. If the STFT shows an increasing trend, the LTFT will increase and allow the STFT to normalize and vice versa. The LTFT stored value in memory can be reset using a bi-directional scan tool or on some vehicles by removing the battery power for 15 minutes.

LTFT and STFT are percentages which represent the adjustment to the fuel injector pulse width. The LTFT and STFT are added together, so a LTFT of 10% and a STFT of -5% will equal 5%. A total fuel trim of 10% will increase fuel delivery with 10% and a total fuel trim of -10% will decrease the fuel delivery with 10%. If any of the value exceed 25% or beneath -25% then the check engine light is turned on with a number of error codes, which can be read using an appropriate scan tool.

Maybe Jaguar does something different? Can you post how Jaguar calculates the LTFT?

They further state that the following conditions must be met for the readings to mean anything.

When using LTFT and STFT for troubleshooting, then the fuel trim must be checked in a number of conditions:

• Cold/Warm engine
• Idle, low and high RPM
• No load, high load (heavy acceleration while driving)

The fuel trims will alter during the above conditions and their altering will provide leads on what is malfunctioning.

Again note that the engine MUST be running for any of these conditions.
I would not use any data retrieved from a non running engine. Just redo it with the engine running so you know the readings are good.
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Yes. Of course the STFT affects the LTFT. If STFT consistently adds or subtracts fuel, over a set period of time, the LTFT is adjusted so that STFT is more likely to only have to adjust a minimal amount. However LTFT does not change for every STFT swing.
LTFT is a bit of a misnomer in that it can change quite frequently, by our human standards. If you watch them, as someone drives, you will get a better understanding of the times to change.
The only differences between each manufacturer and each model of vehicle will be the times and allowed value change before LTFT is updated. And also whether they are using the original style of O2 sensor or the wide range ones. The X350 uses both. The first is wide range and reports in ma changes, these correct the mix in much finer increments than the V swing type. The ones mid cat just indicate rich or lean condition without any usable fine voltage readings.

 

If the engine isn't running or isn't CL (closed loop) the LTFTs can be any value, meaningless or not. Ignore them.

Commonly cars keep many LTFT values, and look up (or calculate) the most appropriate depending on things like rpm, engine load, MAF, etc, providing the engine is running CL.