If someone can help me solving a lean condition issue, I'd appreciated!

I bought a 2002 Ford Focus ZTW (Zetec, at 100k miles) a month ago, and I noticed OBD2 always reads LTFT for both bank 1 and 2 reading pretty high at 10-25%. 10-15% at idle, and goes up at higher RPMs. I haven't seen any trouble codes yet, but gas mileage hasn't been very good. I've ruled out vacuum leak since LTFTs don't improve at high RPMs. The both banks read similar values, so I've concluded the cause is either a dirty/faulty MAF sensor or fuel delivery issue.

I cleaned the MAF sensor with the CRC MAF sensor spray a few days ago with no noticeable improvement.

Today I unplugged the MAF sensor, disconnected the negative battery pole for 10 minutes and started the car. While on idle, OBD2 continuously read STFT (short term fuel trim) high at 10 to 30%, again with similar numbers for both banks. After 5 minutes of idling, the engine stopped by itself.

I'm cleaning the MAF sensor for the second time, this time more thoroughly with isopropyl alchol as well as spray, just in case.

On the fuel-delivery side, the fuel pump was just replaced a month ago (thus ruling out), and the fuel pressure reading on OBD2 is pretty steady around 40psi. I read that a clogged fuel filter affects fuel volume but not always pressure, and with my car having reached 100K miles, I might as well change the filter now.

I've also noticed a small crack on the PCV hose (longer piece), and since this seems a common issue for the model, replacing the PCV valve and hose is next on the list.

Am I on the right track on diagnosing? Anything else I should look into? I would certainly appreciate sharing your knowledge and experience!

  • The ratio of fuel to air is 14.7:1, were you reading the MAF sensor when you were checking the STFT and LTFT
    – user38183
    Oct 6, 2019 at 23:26
  • @hello moto I was - I exported a log including MAF sensor reading from Torque Pro. I got around 2.3 g/s at 700rpm (idle), 10-11 g/s at 1500rpm, around 15 g/s at 2000rpm. My engine is a 2.0L Zetec engine. How do I know if these numbers are good?
    – morezoom
    Oct 6, 2019 at 23:59


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