Quote:
Originally Posted by Radman
I played with my ODBC dongle the other day and noticed my long term fuel trims are at approx -11% for both banks. I also noticed my idle bounces around. It will be at ~900rpm, drop down 600-700rpm and seem rough, then slowly rebound to around 900. Rinse and repeat.
If my understanding of the fuel trims are correct, my car thinks I'm getting too much fuel and is therefore running it lean at times. Would that explain the wandering idle?
If it does, then what should I be hunting for in regards for the reason of the lean fuel trim as my understanding is it should be much closer to 0.
Please be gentle, this is my first time with fuel trims lol!
TIA
Jason
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To just look at just one data point doesn't tell you much.
you need a lot more information to begin any diagnosis.
Your -11% fuel trim can be caused from something as simple as aging sensors.
or high mileage or? or? or?
Long term fuel trims are learned fuel trims. they are learned from short term fuel trims over a period of time. They are affected by things like sensor age, mileage, driving style, even elevation.
What you need to know is what short term fuel trims are doing under the same conditions as the long term fuel trims.
Also what are your O2 signals doing? Whats the MAF signal doing? throttle position sensor signal???
What RPM? what engine load???
You need to know the specific conditions that generates any given data.
If you want to learn about fuel trims, then you have to start with O2 sensor design, function, and there relationship to the DME/ECU.
Go to youtube and look up ScannerDanner and his vids on O2 sensor function and fuel trims. I don't think you will find much better info then he provides.
your hunting RPM could be due to a dirty MAF sensor.
"-But that is just a guess without more info-".
You could try cleaning it and see if it helps.
Get some spray MAF cleaner. Don't use anything else.
Don't touch any part of the sensor except the plastic housing.
Don't touch the little wire if it is the hot wire type, or don't touch the little plastic looking film if it is the hot film type.
Spray the sensor with the cleaner let it dry well, then replace it and see if it helps.
If nothing changes after cleaning the MAF start looking for vacuum leaks.