Fuel trim question – 98 Honda Civic

[My Nameis]

Have a 98 civic EX all stock. Today out of curiosity I wanted to check the fuel trim levels. Currently car runs with no issues but a slight exhaust leak before the catalytic converter.

With engine warm in closed loop at idle I observed fuel trim and short term was fluctuating between +3-7%. Long term was at +4-5%

I was wondering if the long term trim was within a “normal” range. I read a while back somewhere that these cars are meant to run lean at idle for fuel economy, but not sure how true that is.

Currently looks like it’s running lean so fuel is being added thus the +% values.

Curious for inputs. At idle the car isn’t 100% smooth you can feel tiny vibrations but at 185k I attributed that to normal

Topic

[Richard Kirshy]

If your total ( both STFT and LTFT ) when combined are near 0 +/- 10 your good.

[Rich]

Fuel trim is usually measured against another value – often engine RPM. Rev the engine to 2000 rpm or so. How do your readings change? There’s more here:

[Author]

Replies