strange change in commanded afr during idle

[draz53]

I noticed in a recent scan that in the middle of an extended idling period, the commanded afr suddenly went lean (15.75) and o2's pegged low for 7 seconds, then went rich (13.98) and o2's went high (but not max high) for 6 seconds, then went back to normal (14.63). Could this be for an emissions test or some kind of test that gets run when the OS is "idle"? I can't find anywhere in the tune that would set the EQ ratio to less than 1.0, for any reason. This is closed loop, idle settings are all stock, and the actual idle speed didn't change much during this whatever it was.

[mowton]

CATALYTIC Converter test......ECM 302 for Gen IV's, no way to shut off for Gen III's I believe..

Ed M

[5FDP]

If your rear o2 sensors are removed, install them again and just zip tie them out of the way. That will stop the CAT test.

[mowton]

If your rear o2 sensors are removed, install them again and just zip tie them out of the way. That will stop the CAT test.

Right, thanks, I read that but forgot that remedy....haven't tried it myself yet.

Its not really a problem as it ocurrs once a start cycle and is only 10-15 secs long...at least this one changes the commanded lam/AFR :-)

Ed M

[draz53]

If your rear o2 sensors are removed, install them again and just zip tie them out of the way. That will stop the CAT test.

Well if that's the case then that's not what was happening in my scan, since I have stock cats and rear o2 sensors.

[Boosted53f]

Well if that's the case then that's not what was happening in my scan, since I have stock cats and rear o2 sensors.

what car and pcm is this? what does your open loop FA table look like in low map during operating temps?

[mowton]

Well if that's the case then that's not what was happening in my scan, since I have stock cats and rear o2 sensors.

Then the cat test is going to happen...can't stop it. Again its only for 10-15 seconds and once a drive cycle.

EdM

[Boosted53f]

Then the cat test is going to happen...can't stop it. Again its only for 10-15 seconds and once a drive cycle.

EdM

good to know havent seen this