Closed loop issue

[Gelf VXR]

I put a pair of stock O2 sensors back in after removing the WB LC-1 NB simulated, Ive got to get the headers off and put in extra bungs for the WB sensors. Anyway, i bought couple of cheap sensors of ebay and put them in, but it failed the emissions test at natural idle (they let it go thou).

I logged front and rear O2 from cold start for 12 minutes, just the 4 sensors to get the highest frame rate, whats strange is that both the rear O2 eventually go rich, my understanding was the rear O2's should remain around 450mv confirming the front O2 operation and the CATS are efficient.


Anyone seen this before, is it the cheap O2 sensors ( i got another pair to try out now), air leak in the exhaust causing the rear to drift rich and or dead CATS?

[joecar]

Hi Gelf,

The rear NBO2's will respond, but with a long delay (10's of seconds after the front NBO2's)...

typically, conditions vary within seconds (or less), so you will only see this at WOT and at idle.


But if you notice your pic, HO2S12 is responding sooner than HO2S22, but it may still be ok.



DTC P0420/P0430 runs the catalyst efficiency test which at idle commands a definite fueling step (it can be either be up/down EQR 1.0 -> 1.08 -> 0.92 -> 1.0 or vice-versa), and it measures the time that the rear NBO2's take to respond to the front NBO2's, and if the time is less than some constant (something like 10 seconds) then the test fails and the DTC is activated.

[joecar]

From your log I see that the front NBO2's are swinging too slow (should be about 0.2-0.4s period).