tesna

The day has come, UPS has delivered o2 sensors to my office. Immediately I go to nearby exhaust shop during lunch break (btw this time I only replaced the upstream only as the downstream can purchased locally). I want to see if there's improvement


bosch wideband

part no

compared old vs new (not my hand )

bosch

bosch connector

original from the car

original

original

After finishing the install and starting the engine, no CEL, so it seems the install went OK. The LTFT has not coming down much yet, as its only 3km drive to the office. From quick check now the rear o2 sensor reads 0.45-0.5v during idle (previously was like 0.65v) so I hope this is some improvement? I tried to graph it on my launch it seems its steady during idle. When going in traffic it goes up and down (forgot to took a photo)

Let see on longer term. Or should I reset all adaptation values? I hope this will (finally) fix my LTFT

tesna

it seems the new upstream o2 sensors does not improve much on fuel trim after resetting the adaptation values I drove back home (its only 5km away) the LTFT immediately rose from 0 to 8%. Perhaps tomorrow it will get increased further.

If there is vacuum leak, when revving the engine to 2000rpm it will bring STFT to negative value for a little bit until ithe LTFT gets updated to new value (decrease) then STFT go back to 0% right? in my case nope, I rev the engine tp 2000ish rpm but the STFT stays at 0% and no change to LTFT.


rev to 2000-ish rpm


I tried to graph the rear downstream voltages, it seems one of them a little bit lazy


lazy rear o2 sensor?


downstream voltages

according to new upstream o2 sensors both bank lambda should be at 1 however the downstream said nopeeee its got different values on bank 1 and bank 2.

Possible for lazy downstream o2 sensor causing bad LTFT? both did drop to 0v when I play with the accelerator pedal.

DAMMIT ITS DRIVING ME NUTSS I'll be ordering downstream o2 sensors locally next week (starting tomorrow I'll be travelling for a few days)

S-Prihadi

When you are back from out of town, do emission test before replacing rear 02 sensors.
Use the car more, let the fuel trim table adapt to new front lambda sensors.
If your rear o2 is that lazy, your HC may not be at its best lowest, because CAT does remove HC and it need healthy rear o2 sensors to make CAT work properly.


When rear 02 sensors replaced, use the car some distance and do emission test again.
Make sure you do both exhaust L and R side for both emission tests....it will be a good data to have both.

This time when doing emission test ( twice ), make sure when the machine is warming up in free air, the machine oxygen sensor must read proper 20.95% +- 0.2 percent.
Take note of the emission machine Lambda value during test and at the same time use your Launch to see your front lambda sensors value too.


LTFT within +-10% is OK. Mine can be -8% and up to -12% at times, depending how I drive and it is minus sign because my setting is slightly enriched.
Remember that based on last failed emission test, your front lambda sensors were reading false rich, it was nice 0.99 of Left Bank and a mild lean 1.02 for Right Bank
while emission machine was reading a lot more lean at lambda 1.056 ( basic value ) and lambda 1.060 ( RON 93 setting ) assumed on Right Bank.



What we want to see is the new lambda sensor value on your engine must match the emission test machine , of course we assume the emission test machine lambda sensor is good and by then
you will pass the emission test.


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Rev-ing up engine in neutral gear only changes the short term fuel trim the very second the engine rise to 2,000 RPM , very short spike up and then ST fuel trim will stabilize when that 2,000 RPM is maintained.
If you kick down fast the throttle pedal ( at neutral ) say once every 2 seconds to 4,000 RPM and do this for 15 seconds, you will see ST fuel trim increase.more.

If there is a vacuum leak ....while at idle 650 RPM, the idling fuel trim, the total of LTFT and STFT will be higher ( let say total 20% ) than when the idle is raised to 2,000 RPM , meaning the total fuel trim will decrease ( let say 10% ) at 2,000 RPM.

Actually fuel trim is to be read as total : LTFT and STFT.
If the ECM wants zero STFT, it then adjust the LTFT accordingly so that least value for STFT.