tonytherunner
Active Member
How is your fuel trim now ? will be interesting to see the difference.
andyfreelandy
Well-Known Member
Didn't log it in the failed state I am afraid. Can record it with working O2?
tonytherunner
Active Member
Yep is good to have some reference about them STFT and LTFT .
andyfreelandy
Well-Known Member
Fuel trim graph. Long term, short term and sensor 1. If anyone can explain this it would be great! I think it is the change to provide optimum fuel air mix but why 3 monitor points? 14.7 to 1 also rings a distant bell!!! This is on the 1.8k that passed emissions test.
rob_bell
Well-Known Member
This seems a good explanation: https://www.obd-codes.com/faq/fuel-trims.php
Not sure I understand your trace though (not your fault - it is what the gauge is showing) - because the long term appears to be mapping the short term fuel trim???
My hunch is that MEMS3 doesn't output the fuel trims in quite the way the reader is expecting - and there are different ways of obtaining these numbers depending on the way the tool was designed. That doesn't make sense either, because shouldn't MEMS3 be EOBD compliant?
I need to figure this out some time as I remain baffled...
Not sure I understand your trace though (not your fault - it is what the gauge is showing) - because the long term appears to be mapping the short term fuel trim???
My hunch is that MEMS3 doesn't output the fuel trims in quite the way the reader is expecting - and there are different ways of obtaining these numbers depending on the way the tool was designed. That doesn't make sense either, because shouldn't MEMS3 be EOBD compliant?
I need to figure this out some time as I remain baffled...
andyfreelandy
Well-Known Member
They look the same cos I think you misread the key!! Red is long term. Key has description after colour!!
Nodge68
Well-Known Member
andyfreelandy
Well-Known Member
Wos the dips for??
tonytherunner
Active Member
The upstream o2 sensor is the main sensor used for closed loop fuelling. The downstream
sensor is used to monitor the performance of the main catalyst and to trim the fuelling provided by the pre-catalyst
sensor.
If LTFT is adding or removing fuel, it means there is a persistent condition. You then look at what is causing the condition. Such as if LTFT is adding fuel, you look for unmetered air getting in or the amount of actual fuel being injected is not as much as the computer believes is being added based on injector on-time and fuel system pressure.
STFT on your pics detect rich exhaust and make adjustment to subtract fuel .
sensor is used to monitor the performance of the main catalyst and to trim the fuelling provided by the pre-catalyst
sensor.
If LTFT is adding or removing fuel, it means there is a persistent condition. You then look at what is causing the condition. Such as if LTFT is adding fuel, you look for unmetered air getting in or the amount of actual fuel being injected is not as much as the computer believes is being added based on injector on-time and fuel system pressure.
STFT on your pics detect rich exhaust and make adjustment to subtract fuel .
rob_bell
Well-Known Member
Ah! That'll be why.
Yes, that makes far more sense. And the STFT will generally match the Lambda signal.
tonytherunner
Active Member
STFT will generally match the Lambda signal. False
Only thing what ecu want is to archive is AFR ratio 14.7to 1 so STFT can be - 10 to +10 .
Only thing what ecu want is to archive is AFR ratio 14.7to 1 so STFT can be - 10 to +10 .
tonytherunner
Active Member
That it right ,
if i look at STFT the ecu want to be close to zero so if i need to subtract or add too much fuel will calculate and increase or decrease LTFT,
if i look at STFT the ecu want to be close to zero so if i need to subtract or add too much fuel will calculate and increase or decrease LTFT,
