2005 Hyundai Elantra/199k/automatic/OBD P0420 & P0171
Can't shake the -15 LTFT. STFT doesn't vary too much from zero. Cleaned and reset the MAF; replaced the spark plugs (NKG); there are no air leaks I can find; air filter is clean; added fuel injector/catalytic cleaner (which made the 420 code go away for a bit). Scan tool live data shows the O2 sensors reacting as I drive (I presume properly).
I did see a reduction from -21 to -16 when I cleaned the MAF, and a decrease from -16 to -15 when I replaced the spark plugs. The old plugs were dry. The cleaner seemed to make the car run a bit smoother. Car starts readily and otherwise runs well at all speeds. I saw on some Hyundai forums that I can reset the MAP sensor, but I can't find it (suppose to be on the surge tank).
That’s rich not lean.
@imperator It's a bit confusing. The code says lean but the fuel trims say rich.
Might have something to do with the cat code. Time to look at the exhaust system.
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Your scanner's codes aren't matching what you're reporting. (-trim# is rich, +trim# is lean)OBD P0420 & P0171
Is the MAF responding correctly in live data mode? since you have a 2 liter engine it should be near 2g/s ..
^ 2 g/s at idle
Yes, the MAF is responsive, showed 2.48g/s @700rpmHere's a better way to test the MAF sensor's functionality using calculated load: https://www.youtube.com/watch?v=h8RJ4cDwnV0&t=391s
The engine is running rich which can cause catalytic converter issues. Using Cataclean won't fix a clogged/bad catalytic converter. The converter should be tested to see if it's restricting the air flow: https://youtu.be/qJTmddbOxMk?t=18
Could this just be a bad O2 sensor--it would be the third one in 4 years (I am buying name brand ones)
Are you using OEM parts? Name brand parts are good but still there are tons of counterfeit parts out there.
Also saw people mentioning fuel regulator and PVC valve.
Why not test them and find out?
I have no gas smell under the hood...
Irrelevant. PCV valve and Fuel pressure regulator could still be bad even if you don't smell gas. You should test them both to find out if they're working properly.
Sorry, brain farted on that...I am running rich. Yes, the MAF is responsive, showed 2.48g/s @700rpm
checked out the cat pressure; all good. My scanner doesn't have calc value option. Could this just be a bad O2 sensor--it would be the third one in 4 years (I am buying name brand ones). Also saw people mentioning fuel regulator and PVC valve. I have no gas smell under the hood...