Honda Civic 2007 90km odometer Problem- Fuel consumption I have scanned my car and it shows STFT -9% along with below parameters.

  1. Coolant temp -> 64
  2. LTFT -> -7.03
  3. Oxygen sensor voltage -> .55v
  4. EGR Error -> 99 %
  5. Commandent EGR Duty -> 0%
  6. Commandent evaportaive purge -> 22%
  7. MAF flow rate - 2.7g/sec

I understand that if STFT is in negative then this is rich condition and it can impact fuel consumption widely. and the cause could be leak, fuel injector issue etc.

Any insights why my vehicle is not up to mart for mileage(fuel consumption) Pls let me know if I need to share more data about this.

  • In what driving condition where these values obtained? Does it run bad? Is your EGR stuck?
    – Daniel
    Sep 11 '18 at 13:59
  • And what is the make, model, year and mileage of your car ...
    – Daniel
    Sep 11 '18 at 14:01
  • updated model year mileage
    – Pedantic
    Sep 11 '18 at 14:08
  • I see your other question and it suggests you did not really measure fuel consumption over a meaningful distance. Maybe that is your problem?
    – Daniel
    Sep 11 '18 at 14:10

You most probably have a leak in your intake system AFTER your MAF sensor. So your MAF sensor reads that you're getting x amount of air, but more is sucked in (or is lost if you have a turbo and it is currently boosting), so you're running slightly richer than you should be. Your ECU sees you're running rich, and adjusts the amount of fuel using the fuel trim.

  • 1
    That sounds weird to me. Usually people have unmetered air entering, not metered air escaping. Maybe this can only happen on the intake tube, where there is not a vacuum yet? Sep 11 '18 at 14:55
  • Yeah you're right. I'm used to chasing down boost leaks in my Subaru. Will update. Sep 11 '18 at 14:55
  • When I apply brakes after speeding up it makes a very thin hissing sound, however brake works well (Initially I guess this could be due to brake booster, then I checked the break booster by pressing it when car is not running and it should feel harder to press after couple of presses. and it was working as it should be). Is that sound can be related to any leak in the car. I will try to add mp3 file of the sound.
    – Pedantic
    Sep 11 '18 at 23:47
  • It won't be necessary to go to all that trouble. You're hearing air escape from somewhere AND you have weird fuel trims so it's obvious that you have a vacuum leak. A workshop can blow smoke into your intake and see where it comes out again. That would be your leak. Sep 12 '18 at 7:14

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