Tuesday, October 14, 2008

More observations on LTFT

I've really been pushing the fuel injection hard as I've approached 50% ethanol.

It looks like my long term fuel trim at cruise is 24.

It also looks like LTFT is incapable of going over 25. Thus, there seems to be a risk of running lean, and pushing the ethanol content much further might not be a good idea.

It's hard to tell what the O2 sensor is going, the Scangauge scales the output from 0 to 100. I'm not exactly sure how to read it. It does bounce around alot. It will be 8 one second, and 72 the next. So I'm guessing that I'm not consistantly lean.


Anonymous said...

Buzz- try looking into your scan tool's O2 sensor data for the report from your Saab's ECM. If I remember correctly mine reported the rich/lean threshold data and I remember being suprised that mine was considerably different for the Saab than for the Ford (ie 6/10v vs 4/10v).

buzzcut said...

The scangauge reports 02 data on a scale of 0 to 100 (actually, I saw 102 on startup!).

I have no idea what the scale means. What is lean? What is rich? Can't tell.

Alls I knows is that it isn't consistantly one way or the other. It's all over the place, even at cruise.

Anonymous said...

Buzz- in the ECM on my scan tool is a static reading of O2 perameters. It should give you not the run history but instead the design/program range for lean and rich. Ie- Rich over 6/10 V and lean <6/10v. Even if yours are wideband I would think this programmed rich/lean info will be in the ECU along with the O2 type.
I will go see if I can pull this out tonight unless I get interupted with something else I am working on.

Anonymous said...

Ok- here it is Buzz;

W/O engine running I went into the diagnostic monitor test section of the ECU. O2 sensor B1S1 rich-lean thresh module $00 max 0.600v / lean-rich 0.300v / min V value during test= 0.00v / max value during test 1.25v/ meas 0.200v / max 54 cnts/ min 0 cnts

See if you can find such a section in your ECU. The above info is from my Saab. Over 0.6 V is rich and < 0.3 V is lean. If you hung onto my scans from last summer you will find my O2 data all over the place. Narrow band sensors have to constantly go rich to lean, back to rich, and cannot sit in one place. Trouble would come if you ran out of ability to dump enough fuel to go rich for that instant as this would indicate you do not have enough trim authority, pump, or injector to deliver the fuel needed.

At least that is my take on it right or wrong--