Datalog playback

[slvrbullit]

Did some logging with the tune I got from a EEC tuning member. First one, was mainly just a start up and idle log, all numbers looked fine until about timeline 81 then the numbers went to negative. The next two logs however had some strange numbers. I think it is the STFT's and LTFT's that were giving - numbers in the playback. This is a first for me and was curious if any one else had this happen. I can send the logs to someone to see if they get the same out come.

[86GT]

The numbers going into the negative range is perfectly normal. The LTFT are the rolling average fuel trims. Ford's technical boards state that if the remain in the -+ 7% then they are ok. The STFT are the instant feed back from the O2's. It is typicall to see thes go +17 or so during acceleration and - during decel.

[slvrbullit]

Cool, thanks for the info Clint.

[86GT]

This might help too. This is what I have in the EA for the help file

Fuel Trims
Below are the definitions of fuel trims. Long Term Fuel Trim (LTFT) and Keep Alive Memory reference (KAMRF) are one in the same whereas Short Term Fuel Trim (STFT) and LAMBSE are one in the same.

LTFT
Long Term Fuel Trim is a learned value over time. This value changes gradually in response to conditions fuel mixture, engine wear, air leaks, variation in fuel pressure and so on. Long Term Fuel Trim is stored in a nonvolatile memory called RAM and is not erased when the engine is shut down. This information is used during all operational conditions such as WOT, Startup, Part Throttle and so on.

STFT
Short Term Trim is instantaneous correction value determined from the heated oxygen sensor (HEGO) readings. Under normal conditions the HEGO cycles plus or minus a predefined amount around 0.5 volts at a predetermined rate. This only applies to closed loop operations. Short Term Fuel Trim is a correction to the commanded fuel mixture based off the feedback from the HEGO. When Short Term trim exceeds plus or minus 10 percent for too long, the Long Term trim begins changing to bring the Short term trim back within range. Short term trim can vary as much as plus or minus 25 percent,. The above correction logic works to keep STFT within plus or minus some predetermined percentage.

LAMBSE
Some loggers will log LAMBSE. The LAMBSE and STFT parameters are one in the same, but they are displayed differently. The TwEECer will display LAMBSE as a commanded AFR with a value ranging from 10-20 whereas the EEC Tuner will display LAMBSE as a multiplier with a value ranging from .75 to 1.25.

Lambda not LAMBSE has a value of 14.64 which is what the EEC uses for all closed loop fuel calculations. The LAMBSE or STFT is a multiplier for the lambda. This means that if you multiply lambda (14.64) by a multiplier of 0.89 you get a commanded AFR of 13.02. This is what the TwEECer displays whereas the EEC tuner only displays the multiplier. This means that a multiplier smaller than 1 will richening the mixture and vise versa.

When OBDII was introduced in late 1995 the industry standard changed the way LAMBSE was displayed. It is now called Short Term Fuel Trim and is represented by a percentage. In our example above with a LAMBSE multiplier of 0.89 is equal to a STFT value of -9%. Negative percentages are pulling fuel out meaning the vehicle is running rich. And positive percentages are adding fuel meaning the vehicle is running lean.

KAMRF
Some loggers will log KAMRF. The KAMRF and LTFT parameters are one in the same, but they are displayed differently. The TwEECer and EEC Tuner will display KAMRF as a multiplier with a value ranging from .75 to 1.25.

The KAMRF or LTFT is another multiplier for the lambda mentioned in the above LAMBSE section. KAMRF is the inverse of LTFT. This means when KAMRF is .97 the LTFT is -3%. By making LTFT the inverse of KAMRF, both the STFT and LTFT can be added to get an overall fuel trim. This overall fuel trim is then multiplied by lambda. This means a multiplier smaller than 1 will richen the mixture and vise versa. If KAMRF is used then a value greater than one will richen the mixture and vise versa.

When OBDII was introduced in late 1995 the industry standard changed the way KAMRF was displayed. It is now called Long Term Fuel Trim and is represented by a percentage. The KAMRF or LTFT values are stored in the EEC’s non volatile memory for future reference. The EEC will store the KAMRF or LTFT in an 8 X 10 table depending on the current load and RPM of the engine. There is a 8 X 10 table for each bank of the engine

The goal is to have a both the STFT and LTFT equal to zero. Most EEC’s will set the check engine light if the sums of the fuel trims are greater than 40%. Let’s take an example of a MAF that gets contaminated with bugs or dirt. This will cause the MAF to send a lower than normal air flow signal to the EEC. Let’s say it is 10% less air flow. This causes the EEC to calculate a 10 % lower injector pulse width. The oxygen sensors will detect a lean mixture because the lower calculated injector pulse width. The STFT will increase 10% to compensate for the lack of fuel. This will cause the EEC to multiply its final fuel calculation by 10%.

If this condition continues the EEC will take the 10% STFT and store it in the tables as 10% LTFT. This will cause the STFT to decrease back to 0%. It is said that learning is complete when STFT are as close to zero as possible. However this does not mean that there is not fuel trim. Remember that the STFT and LTFT are added to get a final fuel trim. This simply means the EEC has learned to correct for the contaminated MAF.