I've heard that leaky headers can corrupt the O2 readings by drawing air into the exhaust stream and making the readings come out lean. Anyone know if it's possible for a leak downstream of the sensor to cause a lean reading?

I can't seem to throw enough gas at my idle to get the BLM's much under 150. I've searched and searched for leaks and I know I have a slight one at the point where my two sides come together, but that's a few feet down from the O2. Could that possibly be my problem? It's hard to imagine air going that far against the flow...

 

Generally, more then a foot or so away shouldn't, YMMV.
Might try backing the timing down.

 

I have an update to this, which maybe I'll want to put in a new thread to get more eyes on it, but bottom line is that I couldn't seem to up the VE enough to make the O2 happy - I went from 17% in my idle cell all the way to 30% with very little effect.

So last night I tried messing with the BPW instead, it started out at 135 in the stock bin. I pushed it first to 150 to see what would happen, and the BLM went right down to 140. So I went ahead and blasted it all the way up to 175. Lucky guess, and now the BLM at idle is right on 128. But what the heck? Isn't that way off for a mostly stock (open air cleaner and headers) engine? I wonder what I'm compensating for.

Thing is, the engine seems happy, it's not like raw gas is pouring out the tailpipe. So maybe chasing the O2 sensor was a blind alley.

 

Did you have to bring all the other VEs down to compensate for that change?
I'm thinking that it will effect the entire tables, yes/no?

 

Certainly. I haven't even dared hit the road with this PROM so radical. If the BPW is increased, all the VEs would have to be lowered to keep the fuel delivery the same. In my case, all my VE's were a little low (lean), but I was extremely lean at idle. If I drove around with this PROM, I think most of the VE's would come out rich now.

But then, there's something I'm not getting right about all this, since I couldn't seem to get the desired effect with VE alone.

Maybe the EGR isn't really turned off like I think? I believe the fuel would be cut down when the EGR is active since there's less usable air going in...

The other idea, maybe the injectors are smaller than stock ones for some reason. I wonder if some applications use smaller injectors than are expected by my 5.7L bin?