6
votes
P0171 and Fuel Trims
Great question, you supplied enough data to give direction and this is a common problem.
This pattern of fuel trim behavior, higher positive at idle than at cruise speeds, is commonly seen when the ...
- 11.7k
2
votes
What does the ECU use the long term fuel trim for?
This isn't a 100% verified answer yet. I will search for more direct sources when I have time.
Pᴀᴜʟsᴛᴇʀ2's comment got me thinking about the obvious question:
If it didn't need it for something, ...
- 4,910
1
vote
Should the PCV breather hose affect fuel trims?
With the pipe disconnected and open to the air (not plugged), as you say, unmetered air will be getting in, bypassing the air flow meter. Therefore the mixture calculated by the engine ECU using ...
- 25.5k
1
vote
Cleaned MAF sensor and long term fuel trim dropped to -10%
Your engine is not running rich, a negative fuel trim means that the ECU has reduced the fuel in the fuel-air mix to keep it from being rich.
If your MAF was dirty and under-reporting air flow before ...
- 17.7k
1
vote
Are mineral oil smoke test machines sensor safe?
If you apply the smoke to the pipes and sensors for extended periods of time (weeks or months) then most likely yes.
However, for a 1 off short period to find a fault probably not - this does assume ...
- 34.7k
1
vote
Accepted
Why does my LTFT1 make wilder, faster changes than STFT1?
Long term fuel trims are stored values in this model. These are stored for various engine load ranges. They are changed when the short term trims exceed predetermined limits, then the new values are ...
- 11.7k
1
vote
Accepted
Can fuel trim (LTFT) be too high or too low? Not using stock injectors
By using this fuel injector calculator, your new injectors are flowing 24.2 lb/hr @ 49psi, which is a bit more than stock (by 1.0 lb/hr). This could definitely be why you're seeing LTFT levels being ...
- 162k
1
vote
Help on diagnosing positive Long term fuel trim
+- 5% for LTFT is ordinary. +- 15% is more concerning but still not detrimental.
If you see +-30% then you should worry.
That said, the smaller the problem the harder it is going to be finding it. ...
- 16.1k
1
vote
High O2 voltage paired with high LTFT reading
The O2 reading is odd given the LTFT, but if it were me I would start with the obvious basics... The KISS rule is and always will be in full effect.
Check for vaccuum leaks. Even small ones. That ...
- 12.4k
1
vote
What is the the base fuel calculation in a fuel injected vehicle based on?
This is for the 80's-90's Dodge ECU. A bit out of date, and for a MAP (not MAF) system, but has some good info. http://thedodgegarage.com/turbo_pfi.html
It will vary by manufacturer, but ...
- 8,448
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