High Negative Fuel trim
Hey Scotty, I’ve been having issues with high negative fuel trim. 2002 Honda civic ex coupe D17A2 205k miles. I’ve been using a Bluetooth obd2 scanner to monitor live data and have noticed my short term fuel trims are running negative, even at idle they fluctuate around -11% up to -15% at times. My idle feels rough and almost like an occasional misfire but no CEL. When I’m driving for example going 45mph and I let off the gas I will sometimes feel a jerk and I notice when the engine does that the fuel trims will drop even more negative. I have changed my oil and filter, changed all my spark plugs, checked vacuum, rebuilt entire exhaust to endure no leaks. I noticed my upstream o2 sensor was not switching as fast as what I think it should comparing it to videos I’ve seen on YouTube. I have a new upstream o2 sensor on its way soon. If this doesn’t fix the negative fuel trim, what should my next step be? Thank you!
have you checked the engine air filter?
Maybe one or more fuel injectors aren't spraying properly. Have an injector balance test done by a mechanic or run some cleaner through it first.
Wish I could upload the screen recording.
just get the youtube app on your phone and upload it there.
After starting it up the short term fuel trim fluctuated
STFT is supposed to fluctuate. It's the long term you should pay attention to.
You also didn't say if this was idling, or driving or what.
When you change O2 sensors or anything like that, the computer has to perform a fuel trim relearn which takes a bit of driving.
Intake Manifold Preasure was fluctuating also I noticed when it would jump as high as 90kpa
This isn't terribly useful information without knowing the throttle position, engine RPM, etc.
90kPa is still a partial vacuum.