using Datamaster $8D The last last few logs I was very rich in upper VE (9.0) with WBo2. BLMs were high (lean) in these areas? So I looked for any leaks (cast iron corvette 2.5 in.) manifolds. NBo2 6in from manifold exit. NO DTC's in the log and now when I attempt to log when the proper temp is reached the log reports open loop no closed loop? Could the NBo2 be fouled from the rich condition? if the problem is with the NBo2 why no DTC?

 

I would try unplugging the NB and resetting the ECM. With no o2 sensor it should run rich but not that rich. If a bad o2 sensor thinks it's lean it will add more fuel. I had the opposite problem. NB said rich and was taking out fuel. WB said lean 20. No DTC. Both WB and NB sensors were new. Replaced the NB again and problem solved.

 

Thank you for the reply. Easy enough done.
Just curious that the ECM doesn't set a DTC? I am trying to resist the temptation to start replacing sensors. I want to understand how to diagnose what may be early symptoms of a failing NBo2 etc. I won't learn if I just luck out and guess right. I want to learn what things to look for in my logs eg., NBo2 switching / voltages and other diagnostic tests that I can perform to be certain that I'm on the right track.

 

Of the available stock AFS-21/22 single wire NBo2 sensors which manufacturer is closest to the original AC Delco since these are made by Bosch now? Denso?