Lean AFR at mid rpm range
01-01-2015 | 08:22 PM
#1
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Lean AFR at mid rpm range
Hi,
Car is a 06 6MT NA and all was fine until recently when i tried to do a WOT pull, i found my AFR went to 15.+ from about 3k-7k rpm after which it will settle to about 12-13. happened on all gears, day or night. No CEL. Cat deleted, RB air intake, BHR ignition.
first thing i do is the 20 brakes to reset the ecu but it still happened, found that my LTFT did not reset at all. next i disconnected my battery to reset and now my LTFT resets to zero and my mid rpm lean AFR doesn't happen anymore.
about one month later, the same thing happened again and true enough, i disconnected my battery to reset and all will be fine again.
what could have caused my mid rpm lean AFR?
Car is a 06 6MT NA and all was fine until recently when i tried to do a WOT pull, i found my AFR went to 15.+ from about 3k-7k rpm after which it will settle to about 12-13. happened on all gears, day or night. No CEL. Cat deleted, RB air intake, BHR ignition.
first thing i do is the 20 brakes to reset the ecu but it still happened, found that my LTFT did not reset at all. next i disconnected my battery to reset and now my LTFT resets to zero and my mid rpm lean AFR doesn't happen anymore.
about one month later, the same thing happened again and true enough, i disconnected my battery to reset and all will be fine again.
what could have caused my mid rpm lean AFR?
01-02-2015 | 06:10 AM
#4
Which is exactly why the PCM doesn't determine or set LTFT during WOT. It determines different LTFT settings at closed-loop idle and cruise operation. It then transfers LTFT values from cruise over against the WOT fuel map settings. You need a proper log file to determine this. Then you need to determine what is causing LTFT to go off during cruise and also part of the equation is whether or not idle LTFT is trending the same of not. The proper diagnosis and resolution requires the proper tools and understanding. It's not a simple "get an answer on the internet" solution.
01-02-2015 | 09:31 AM
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hi Team, so you are suspecting that something is wrong with my cruise ltft which is causing my lean AFR at mid rpm...hmm...
after I reset the ecu, it is ok now. I will do some data logs when it happens again. tks for the tips.
after I reset the ecu, it is ok now. I will do some data logs when it happens again. tks for the tips.
Last edited by 4DRcoupe; 01-02-2015 at 09:34 AM.
01-02-2015 | 11:58 AM
#6
Given the little actual info provided only an assumption can be made. Loki asked for data, not what obd2 reader you have. Unless there is something to actually clear in LTFT then the end result as you presented it makes no sense. Hope you can figure it out.
Btw, 20 brake stomp is not for clearing LTFT.
Btw, 20 brake stomp is not for clearing LTFT.
01-02-2015 | 09:25 PM
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thanks Team....
right now i'm just thinking through and correct me if i'm wrong.
the front O2 is the one reading and giving the AFR and if it's reading rich, it will make the LTFT to be -% and pulling fuel. currently my idle LTFT is -4% (AFR at 14.5-15) and cruise/wot is -11% (AFR at 12.5-13). does this mean that my pcm is pulling fuel in order to reach the AFR?
something is causing the pcm to inject more fuel than needed and the feedback is instructing the pcm to pull fuel? maybe leaky injectors?
right now i'm just thinking through and correct me if i'm wrong.
the front O2 is the one reading and giving the AFR and if it's reading rich, it will make the LTFT to be -% and pulling fuel. currently my idle LTFT is -4% (AFR at 14.5-15) and cruise/wot is -11% (AFR at 12.5-13). does this mean that my pcm is pulling fuel in order to reach the AFR?
something is causing the pcm to inject more fuel than needed and the feedback is instructing the pcm to pull fuel? maybe leaky injectors?
01-04-2015 | 09:28 PM
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MAF volt vs MAF g/s
just a quick question: is the MAF voltage corresponding to the MAF rate g/s?
higher MAF v = higher MAF flow?
can't seem to attach .csv file but i've attached a pic file.
higher MAF v = higher MAF flow?
can't seem to attach .csv file but i've attached a pic file.
Last edited by 4DRcoupe; 01-04-2015 at 09:33 PM.
01-05-2015 | 09:41 PM
#10
...
Diagnosing with Fuel Trims
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
Diagnostic Tip:
For a suspected vacuum leak, note the fuel trims at idle and increase engine speed to 2500 RPM and hold. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, you have a vacuum leak. After the repair, reset the KAM and start the vehicle. Monitor the fuel trims to make sure they are within the normal ranges. It could take up to 10 miles of driving for an accurate LTFT reading.
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
Diagnostic Tip:
For a suspected vacuum leak, note the fuel trims at idle and increase engine speed to 2500 RPM and hold. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, you have a vacuum leak. After the repair, reset the KAM and start the vehicle. Monitor the fuel trims to make sure they are within the normal ranges. It could take up to 10 miles of driving for an accurate LTFT reading.
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