Negative LTFT

2010 GMC ACADIA
50,000 MILES • 3.6L • V6 • 4WD • AUTOMATIC
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FIROJTADAVI
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  • 1 POST
my car giving very low fuel mileage so i scan with Bluedriver obd 2 scan showing -19 to -22 LTFT while idling and at 1,500 rpm's. i changed the air filter,spark plug,clean mass airflow. but no benefit.
Aug 22, 2019 at 7:54 AM
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KASEKENNY
  • ASE Certified Mechanic
  • 18,907 POSTS
  • ASE Certified Mechanic
Hi,

So what are your short term fuel trims on each side? I assume you don't have any codes either?

Negative long term fuel trims just shows the engine has been running extremely rich for a long period of time. So we need to see what the engine is doing currently while running which is what the short term will show.

Assume they are negative as well, we need to measure fuel pressure at key on and then while running at idle. I am also interested to see how long the pressure holds after you shut the engine off. There is a very good chance that you have injectors leaking if the engine is actually running rich. If it is not, then we may have an o2 sensor issue. However, I am hoping that one side is running rich and not both so that way we can swap o2 sensors side to side and see if the rich condition moves with it.

Let me know what you find and we will go from there. Thanks
Aug 22, 2019 at 1:06 PM
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