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
    Commented Sep 11, 2018 at 13:59
  • And what is the make, model, year and mileage of your car ...
    – Daniel
    Commented Sep 11, 2018 at 14:01
  • updated model year mileage
    – Pedantic
    Commented Sep 11, 2018 at 14:08
  • 1
    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
    Commented Sep 11, 2018 at 14:10

3 Answers 3


Captain kenpachi def sounds correct. According to your fuel trims you have an unmetered vacuum leak and along with your confirmation of the sound that you are hearing. It sounds to me that you have a vac leak (or you are just hearing your brake booster) but you still have a leak somewhere and an easy and relatively safe and easy way to test for it if you don't have access to a smoke machine in a machanice shop like i did for the last 38 yrs then you could do it the way that i did it for many years previous to being in a fancy shop. We just took a small propane bottle and cracked it open a slight bit with the flame NOT LIT and the engine idling and slowly waved the propane tip around the intake until you heard the engine rpm's change ever so slightly and then when it did you knew that you had just found the general area of your leak. Easy peasy nice and sleasy. Hope this helps. And sorry for any mistypes. After all, i am just a mechanic (without his readers) lol Bill aka midnightrider


First off, in order to read fuel trim, add your long term and short term together. Your system seems like it has too little oxygen in the exhaust, causing the pcm to restrict fuel to the engine relative to the metered oxygen flowing into the system. This could be caused by a bunch of things. Replace your air filter and check your pcv house for oil. If both are good, pull a spark plug and look at it. If you're not sure what to look for, take a picture and post it here and we'll be happy to help!

Let us know if this helps or how we can clarify the issue


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? Commented Sep 11, 2018 at 14:55
  • Yeah you're right. I'm used to chasing down boost leaks in my Subaru. Will update. Commented Sep 11, 2018 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
    Commented Sep 11, 2018 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. Commented Sep 12, 2018 at 7:14

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .