Hi all from a long time lurker, but only with a few posts. Now I beg your pardon for a long one:
I've an issue on my 2007 Honda Jazz GD (the European version of the Fit, equipped with a 1246cc i-DSI engine). The car has two spark plugs and no VTEC.
Since new the car was fuel thirstier than I expected/hoped.
Several years ago I bought a scangauge and the LTFT value keeps displaying negative numbers.
After a recent 200Km journey on highway it tends to be at -6 LTFT, but while driving around the city I get a typical -10 LTFT, and up to -13 LTFT
Today I checked STFT and while idling it displayed positive values (+2, +3, +1) i.e. it didn't oscillate around 0.
I figured that for some reason the ECU detects too few fuel (a dirty or defective oxy sensor before the cat?), so keeps increasing STFT (and this might explain the high fuel consumption). But - for some reason - another sensor (the sensor after the cat?) senses there is too much fuel (and says LTFT -10).
My issue is that this LTFT doesn't succeed in correcting the general consumption. I.e., the STFT keeps being positive and the consumption is high (while I have no error codes).
What could I do?
I thought I might clean the lambda sensor before the cat. Sometimes ago I installed a non standard header and I thought it should improve the things, but it didn't...
Any idea is welcome.
Thanks for your patience,
Stefano