Fuel trims adjustments by cell?

[M1tch]

Hi there,

I was just wondering if there is any data captured with regards to the fuel trim being set in each of the fuel cells - much like the knock values in the various per cylinder knock tables.

I do have Closed Loop Lambda running with my wideband O2 sensor (set to auto mode), I know that the knock trims can be stored on the ECU for the next start up to adjust the ignition map etc, was wondering if the same was true for the fuel map?

Does the close loop lambda settings mean that the ECU needs to relearn the fueling everytime the car is driven or does it store the trims somewhere to use as a basis?

Thanks in advance!

[dx4picco]

As far as I understand, CL fueling is not a learning thing. Changes are made on the point, that you can follow with the real time value of fuel trim, but even if you come back in the same cell 5 minutes later, its gonna make the adjustment according to the  AFR it reads 5 minutes later.

[Adamw]

There is no "long term fuel trim" type functionality.  You typically want your fuel map to be tuned properly first an only rely on closed loop to make small corrections.  If you are looking for an aid to tune the fuel table then look at the mixture map and "quick trim" functions which allow you to correct the fuel map from logs.

[Monsterbishi]

17 hours ago, Adamw said:

There is no "long term fuel trim" type functionality.  You typically want your fuel map to be tuned properly first an only rely on closed loop to make small corrections.  If you are looking for an aid to tune the fuel table then look at the mixture map and "quick trim" functions which allow you to correct the fuel map from logs.

As far as tuning goes, what functional differences are there between using the mixture map and the quick trim feature?

[thetyrant]

As above no fuel trim stored and its a live system only for small adjustments only, i spent a lot of time on my fuel map using mixture map before switching on closed loop fueling and looks like its paid off as CL correction is generally less  than +/- 5%  

Ive not looked at quicktrim feature i wil take a look at that one for future.

 

 

[Adamw]

Mixture map is used to pull the lambda data out of a whole (large) log.  Since a "whole log" may have lots of conditions that cause the measured lambda to be invalid such as transient conditions, overrun fuel cut and limiters etc you need to carefully select filters to filter out most of the junk.

The quick trim function is used to only focus on one specific point in time in a log - so you can choose an area where things are reasonably steady state.  To use it you have a log and your tune open, set up a page with a time plot showing your common fuel tuning parameters and your fuel table side by side.   Drag your cursor to a point in the log trace that you are interested in - usually where throttle/MAP is reasonably steady, you will notice the crosshairs on the fuel table will show which cell it was working in at that point in time.  You click on that cell to select it, then hit the "M" key to bring up the quick trim.   You just enter the logged lambda value and hit enter and it will correct that cell in the fuel table.

[M1tch]

Thanks for all the comments, my fuel mixture map is usually very close compared to target AFR after doing many road tuning runs, I did however notice that the CLL was working quite hard in some of my idle cells so have already adjusted though - think its now sitting at around 1-2% correction on idle.

Will turn the CLL off again and do a few more logging runs to make sure that there aren't any other cells that were a bit too far out from target - I know that OEM ECUs usually have long term and short term fuel corrections but I guess with a properly tuned fuel map I only need the short term adjustments on the CLL.

[Adamw]

You wont get good results with either of these options with closed loop on, they were designed to work with it off.