Negative Long Term Fuel Trims

[asghar1075.dev]

Dear all please have look at the following graph (time vs o2 volts) of my car's O2 sensor at cold start, idle and after resetting the ecu; please guide is it ok, or should i change it.

@Xulfiqar sir ur guidance please.

[asghar1075.dev]

@dani_kk

[pwuser15860915546]

ur engine rpm r very low, why did u reset ecu, do u have an error code, why do u want o2 sensor voltage data to be analysed ?

[asghar1075.dev]

there was no error code but due to loose terminal, RPM got stable above 700 after idle learn, i want to clarify is it behaving normal or need to be changed.

[asghar1075.dev]

@margallar
@syncview
@sergiofink
@babarhyd

[asghar1075.dev]

Bump!!!!!!!!!!!!!!!!!!!!!!

[pwuser15860915546]

sensors r usually checked by their resistance like my car o2 sensor heating coil resistance is 5.1 - 6.3 ohms. this data u have shared is functionality graph so it needs to be assessed with respect to equipment used

[pwuser15860915546]

just remove 02 sensor, check its resistance and consult ur car repair manual for values

[pwuser15860915546]

o2 sensor
compares outside oxygen with unburnt oxygen in exhaust manifolt
it generates a voltage corresponding to unburnt oxygen
higher voltage means rich mixture
typically this voltage is between 0.1 to 0.9v
the values work in open and closed loop as per car rpm and coolant temperature
usually in idle the values oscillate

apparently ur graph is correct .. but if u have a 3-4 wire o2 sensor then it has a heating coil which starts the o2 sensor and its resistance will tell u if o2 sensor is working or dead

hope its clear now

[Xulfiqar]

the sensor is reporting good swing but its starting to bias towards lean. You will notice that it is maxing at 0.8V. How old is it?

Also do this test when the engine is fully hot

[asghar1075.dev]

Not sure about actual mileage but it looks too old. it was on cold start, initial temp was 31 degrees and towards the end of the graph it was 50 degrees.

[asghar1075.dev]

Actually i dnt have voltmeter.

[asghar1075.dev]

it was done during morning start, engine coolant temp was 31 degrees initially.

[Xulfiqar]

the "resistance" he is mentioning is only for the heater element. it would have spat a code for it , if the heater was open circuit.

[asghar1075.dev]

Following are the readings when engine was hot. please also have a look at Fuel trims.

[Xulfiqar]

Thats a really bad oxygen sensor readout and an incredibly bad fuel trim too

[asghar1075.dev]

So it going to be changed, thank you sir.

[asghar1075.dev]

Sir @Xulfiqar following video shows trims after changing the o2 sensor. LTFT still remains in -ive, please have a look of this.

Edit: air filter is new nd while on idle when pcv valve is removed stft start raising and shifted to +ive.

https://www.youtube.com/watch?v=qTQXC4lg5vY

[asghar1075.dev]

@Xulfiqar shb ur suggestions pleas..

@capsat

[asghar1075.dev]

@rajaatta