do my o2 sensors need replacing
Discussion
1:35 to 3:38 was idling
3:38 to 4:74 was holding it as steady as I could to 3000rpm (neutral standstill) 4:74 on was back to idling. is it normal method of calibration for sensor one to peak and trough like that?
renault k4j engine (2005 megane II 16v 1.4)
full csv file datalog available here if it's of any additional use
any advice appreciated!
http://www3.zippyshare.com/v/51051278/file.html
thanks very much for taking the time to look - interested to know what draws you see that makes you think the catalytic converter's not working well? I'm still learning to interpret the data
should the after-cat sensor be pretty flatline regardless of the engine's load/revs etc?
also, if the cat is shot, could this be whats causing the fuel trim to be high?
should the after-cat sensor be pretty flatline regardless of the engine's load/revs etc?
also, if the cat is shot, could this be whats causing the fuel trim to be high?
Edited by AlVal on Monday 30th May 01:00
The sensors look fine. The pre-cat sensor should oscillate about once per second between about 0.2 and 0.8 volts as it tweaks the fuel mixture to try and keep it steady at 14.7 A/F ratio. It might be oscillating a bit slowly but maybe the system is not sampling the signal very fast. It might also be a dipping a bit low to 0.1 volts but in general it looks ok. Only a proper oscilloscope reading would give you the exact timings I suspect.
The post-cat sensor will mirror the readings from the 1st one if the cat fails or is removed (obviously as the gas content of the exhaust will not change between sensors) but should stay flatline if the cat is working ok and removing exhaust emissions. At idle this is happening fine but at higher throttle openings it looks like the cat is starting to struggle a bit. The actual flatline reading from the 2nd sensor is fairly irrelevant because it depends on whether the cat is using up excess oxygen to burn off CO and HC or producing it to reduce nitrogen oxides back to nitrogen and oxygen.
However NOTHING that happens behind the first sensor affects the engine's operation. The 2nd sensor only triggers a fault code if it starts mirroring the first sensor's fluctuations to indicate cat failure but it has no effect on fueling. Nor does cat failure which only affects actual tailpipe emissions so if the car passes its MOT then leave both alone.
Only if the 1st sensor fails can the engine's operation alter or become faulty.
You might try swapping the sensors and see if the 2nd one reads the same as the 1st in position 1. That would indicate both are operating identically. If one works better in position 1 then leave it there.
I'll attend to your fuel trim issues in the other thread.
The post-cat sensor will mirror the readings from the 1st one if the cat fails or is removed (obviously as the gas content of the exhaust will not change between sensors) but should stay flatline if the cat is working ok and removing exhaust emissions. At idle this is happening fine but at higher throttle openings it looks like the cat is starting to struggle a bit. The actual flatline reading from the 2nd sensor is fairly irrelevant because it depends on whether the cat is using up excess oxygen to burn off CO and HC or producing it to reduce nitrogen oxides back to nitrogen and oxygen.
However NOTHING that happens behind the first sensor affects the engine's operation. The 2nd sensor only triggers a fault code if it starts mirroring the first sensor's fluctuations to indicate cat failure but it has no effect on fueling. Nor does cat failure which only affects actual tailpipe emissions so if the car passes its MOT then leave both alone.
Only if the 1st sensor fails can the engine's operation alter or become faulty.
You might try swapping the sensors and see if the 2nd one reads the same as the 1st in position 1. That would indicate both are operating identically. If one works better in position 1 then leave it there.
I'll attend to your fuel trim issues in the other thread.
I would suggest that the cat is just "cold" after the first idle period (esp if it's an "underfloor" variety??).
The mean value of the downstream sensor is used to trim fuelling, but only for the "jump and hold" trims for lambda perturbation, so will not make much diff to "bulk" AFR target. (cruical for optimised catalyst effy as it ages however, but unlikely to show up on an MOT style "sniff" test)
The mean value of the downstream sensor is used to trim fuelling, but only for the "jump and hold" trims for lambda perturbation, so will not make much diff to "bulk" AFR target. (cruical for optimised catalyst effy as it ages however, but unlikely to show up on an MOT style "sniff" test)
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