165/6E, TPRT. Using MAF table #1 to adjust idle AFR with WBO2 to confirm AFR. Engine warmed up and CL. IAC holding steady, BLM slowing changing back and forth between 128 and 108. When BLM is at 128, AFR is about 14.7, but when BLM drops, AFR goes lean to about 17 at a BLM of 108. Why would the BLM be changing like this when the IAC is steady? Parameters like RPM, and CT are steady. MAF is reading about 11, so I've been changing the MAF table #1 values that are close to 11 up and down and I can see some effect on the AFR when BLM is at 128, but then the BLM drops and the idle leans out.
Any suggestions?

 

when you say it's slowly changing back and forth between 108 and 128, do you mean that it goes straight from 108 to 128 (and doesn't go through any of the values in between), or does it slide up and down through all the values (i.e. when it goes from 108 to 128, it slowly progresses through 110, 112, 114, etc. on up to 128?)

what is your NBO2 doing during this time?

BLM/INT are modified as a result of the readings from the NBO2.

Since your WBO2 shows lean when the BLM goes to 108 (with a "rich" blm, the ECM is pulling fuel out); it sounds like your NBO2 might be reading constantly too high for some untold reason. Is your WBO2 in the same pipe as the NBO2?

i don't think this is a tuning issue, it sounds like some kind of parts failure to me.

more details?

 

Thanks for your reply 91L98Z28. BLM's are slowly changing throughout the range, i.e., it slowly progresses through 110, 112, 114, etc. on up to 128 and back down.
NBO2 is in the driver side header collector. WBO2 is in Y pipe just before pass side "T's" in.
Since posting the original post in this thread, I have become about 99% sure I have a head gasket leak and I'm in the process of removing the heads. I was blowing coolant out of the system into the overflow tank and it wasn't moving back from the tank into the system. I replaced the radiator cap and it still did it. It would blow about a gallon or two into the overflow tank and then have trouble with getting hot when sitting in traffic even with the fan running since the radiator was only about half full. I could also see bubbles being blown into the overflow tank. Several times I felt a considerable miss while driving on the highway.
Anyway, it could be possible that this could have been some/or maybe all of the cause of the BLM drift issue. I'll have to get the motor running again before I know for sure.

 

this raises an interesting question:

we all know that the wrong silicon can poison an o2 sensor.

what about coolant/antifreeze?