Hondata

I have a 17 sport hatch with the 1.5t and have been running the +9 flash for over a year now and over that time I have been slowly learning more things about engines and tunes. So I have noticed my long term trim has been ranging from -8 to -11% for the last 6 months as I have been paying more attention to short and long term trims, is this for concern?

If it matters I only run 94 octane chevron fuel. Knock control stay around 54% but occasionally will jump to 70ish% when bagging on the car. Short term for most trips is usually under-6%.

Do you have an intake on the vehicle?

No engine is completely stock and just running the +9 basemap

That is a little low for the long term trim, and you could adjust the AFM calibration to get it to zero, but I would only do this if you are reflashing the ECU regularly (like every day).

Okay so shouldn’t be an issue then? I only reflash when an update is available. So reflashing daily to keep it down won’t be happening. So should I just ignore it or should I be getting it tuned?

I'd make a datalog and post it here.

I've experienced the same thing, pretty consistently with every flash. +6 or +9psi.

I have a 2018 Sport Hatch MT. I've attached a datalog from a 6psi flash and you can watch the LT Fuel Trim drop from 0% at ignition (fresh reflash), to -10% after 20 mins of driving (mostly highway on cruise control).

Fully stock, as well.

Thanks, guys.

For clarification is the negative value for s and l trims fuel enrichment or fuel leaning?

If the LAF is reading that the exhaust gas is too rich (showing Air Fuel ratios less than 14.7:1), the short term fuel trim goes negative, giving less fuel.

If the short term stays negative for enough time, the long term will start to drop as well.

In the datalog I posted, when they started to drop, the Air Fuel ratio was around 12:1 at cruising speeds. The short term immediately plummeted, and then while it stayed low, you can watch the long term follow it down.