vortec dave

Bank 1 shows LTFT varying from +3.9 to +5.5 (usually 4.7 recently) while Bank 2 shows -0.8 to +0.8 (usually +0.8 recently) fairly consistently now.  Yesterday earlier in day it showed B1 5.5, B2 -0.8 (ltft) at idle, at stoplight (but oil was low the day before and I topped it off that morning), then later in the day after working B1=+4.7, B2= 0.0 idling at stop; when I put it into Park it showed B1 +4.7, B2 -3.1 (neg.)  I could use some help figuring this out. Is the ecu fuel map bank specific?  Can it tell I have bellybutton lint in B1 and not B2?  I haven't figured out how to get a singular value for STFT on my "scanner" because it is always cycling.... 
Before my intake & head gaskets gave, I had the LT's hovering around 0.0, usually a 1.6 difference between them. Since I have been "fixing" this beast (e.g., since I have had it)  it seems like I get "new truck" for 500 to 1000 miles then the ECU catches on and craps its pants again, always something new.  Sometimes it is easy, like a fried wire shorting to ground, sometimes cap rotor, you name it- that old 400k game.     I know the next part I throw at it may well be a crate engine, but I'm as much after answers as mileage.
Background
   Ignoring for the moment that the 97 L31 5.7 vortec puffs blue smoke at every startup with longer than an hour resting time now, I am trying to figure out this LTFT data.  My scanner is an Innova "worthless" (I may have spelled the model wrong.)  Truck is 1997 K1500 Z71 5.7 L31 with 4L60E, 421k miles on it now. It thought it was retiring at 300k.  This summer I pulled the lower intake to fix the coolant leak, that lasted a month before the head gasket said "me too."  So I pulled the heads, and halfway through cleaning them I realized there was warp so I got a pair from pick-a-part and cleaned them up only to find they weren't so great either, ended up using my old B2 head on B1 and one of the pick heads on Bank 2, had them both resurfaced, then lapped the valves (but not enough to suck the old rings out.) Valve stem seals replaced a couple times just to make sure. Felpro positive types. Disassembled the lifters and cleaned them all.  After playing with the heads, I had some #8 plug oil fouling, and blue smoke started after I did the heads, but I had it disappeared for over a month after adding rislone engine polymer stuff (figuring I dropped some snot into #8 while cleaning the deck.)  Note, after the work this summer, I ran out to AZ and back and got 19mpg (before the ign module farted. Yes, I had a spare...don't you?)   
   Just so you know where I am coming from, I could pull the plenum and head covers (including fuel rail, e- connections, moving egr tube/ac compressor, etc. ) blindfolded at this point (really...which is not exactly a good thing) and set the cam retard to within 1.5% by hand without a scan tool (I have done it 3 times and checked it afterwards...) so I have some degree of experience here. On the other hand I am not a mechanic, just someone who could fix his beast in Baja and get it home again.
 

Is there a code or symptom you're after? To be perfectly honest, with a LTFT of 5% on one bank, I'd shut the hood and call it good.

Thanks for responding! I'll take this opportunity to clarify more.
No dtc's. Got one when I left the oil fill cap off once, but otherwise nada.
On this truck there is a direct correlation between lean response ltft and gas consumption. If I got it down to under 1.6 on that side, I'd be getting 16mpg city and 19-20 hwy again even with 400k. It suggests unmetered air into bank 1 to me but I have bubbled and smoked everything and I'm going nuts. Swapped O2 sensors, checked sensor grounds, signals, all that.
The +4.7 is on the bank 1 side and I am looking for whys. I have checked the pcv, I have a remflex on the manifold, I checked the egr tube nuts (replaced the tube a year ago with the manifold.) I have the y pipe donuts tight, I even smoked it through the upstream O2 sensor port. I do have a leak in the y pipe where it turns south to the cat on the passenger side, but that is 2' downstream of the O2 sensor; I have tested the cat temps above and below and they seem to be working.
I am also trying to figure out why Bank 1 LTFT would stay the same in gear vs in park while the Bank 2 LTFT would show 0.0 in gear but negative in park. Bank 1 may be a totally different problem than bank 2.

Just a shot in the dark, but have you looked at the fuel injectors on bank 1? This isn't a TBI, I'm assuming. 

I replaced injectors a couple years ago with MPFI upgrade (actually found they had already been upgraded from the spider poppets, albeit gooey from pcv blowby) and when I tore into the heads this summer, I cleaned the new ones up, flushed the body, and replaced the pressure regulator (and fuel pump again.) At that time I went into the old mfi's to see if they were clogged, etc (rigged a pressure reservoir and tweaked each injector with power- all had decent spray and no clogs) so the "technical" answer is NO, but since the old ones didn't leak and weren't clogged, and I had cleaned up the newer ones plus run a bunch of PEA through them, logic said it wasn't them. My logic could be off. If anyone knows of another test (?pulse width or??) let me know (and recommendations on a scanner that works. ) I'm trying to keep the cost of a scanner and repairs less than the value of the vehicle, though. I thought it might be ecu, but now we're into throwing more parts at it with no verifiable reason. If it was as simple as throwing in another set of $300 injectors, I'd do it! But not just throwing another $300 at it is why I'm here.............. I'm looking for not just the whats, but the whys. Thanks for the feedback, keep it coming!

If you unplugged bank 1 upstream O2, I wonder if your mileage would improve any. You could also disconnect the signal wire on bank 1's upstream and use bank 2's upstream to do the reporting to the PCM for that side. That might not be good for the cat possibly and either scenario would throw codes at you. I know both ideas are more of a hack than any real fix, but just thinking of ways to get your fuel consumption down.

Here's a simpler thought: While it is a fact that a leak in the exhaust manifold will actually suck air into the exhaust (not just expel it) and cause a lean condition at the upstream O2 sensor, what about a leak in the pipe between the upstream O2 sensor and the cat? On the vortec at least in early OBD2 (1997) it is said the ecu does not use the downstream O2 sensor for fuel mix calcs, but could a leak downstream of the upper O2 cause a leaning from 2 feet downstream? I figured the flow in general would prevent that. I had tested the cat temps with an IR gun fore and aft and they seemed to be working correctly, but if there was a minor clog, could that cause flow back up somehow and send the lean leak air forward to the upstream sensor? Could the cat still show life temperature differential wise and also be clogged enough to do that?

I guess the closer a downstream exhaust leak is from an upstream sensor the more it could impact it, but I think that would be on the order of inches rather than anything more. Clog or no clog.

Regarding catalyst temps, I've heard that test really isn't terribly definitive in determining whether the device in plugged or not.

Thanks for that. The temptation is to get a new y-pipe (it comes with cats) or at least drop it and clean it up and weld the leaks, ...if I could figure out how to get it out without dropping the cross member (I read one person say it had been done but it sure doesn't look like it.) I still need to patch that up at some point.
How, then, does one test a cat (for plugged-up-ness or failing)?
Note that at almost 25 years old and 420,000+ miles, I'm really not worried about replacing parts- I expect to! But as I said before, it is as much for the answers...

In my limited experience with clogged cats, the usual symptom has been an engine that bogs down at high load or WOT. Temp gauge might be higher than normal, too. To verify, I usually just remove (and unplug) the upstream O2 and see if performance improves any. If it does, your choices are a restriction or a perhaps a problem with that oxygen sensor.

If you want a more definitive answer, there's a backpressure tester you can use that measures backpressure in the exhaust, You screw it into the upstream and/or downstream O2 bung and look for PSI values over something like 3, which would indicate a problem. I've heard you can also use a vacuum gauge to diagnose a restriction. Eric the car dude looks like he has a pretty good video on how to do it.

There's probably some things under OBD live data that would tip you off to a restriction as well. Perhaps someone more capable than I can comment on that.

There's a few ways to test for a restricted exhaust if that's what you are suspecting. The easiest test with the clearest results in my opinion is to check beck pressure in the exhaust using a gauge.
I have a cheap vacuum gauge from harbor freight that also measures pressure that I use for this. You can remove an O2 sensor before the cat or drill a small hole.
At idle, there should be no pressure.
On snap throttle, I don't want to see more than 3-5psi.
More than that is a clear indication that the exhaust is restricted.
The heat test isn't accurate and pulling an O2 and beating on it is obnoxious and many times inconclusive.
An in cylinder pressure transducer will quickly point to a restricted exhaust, but that's generally out of the reach of most DIYers.
Also, I've never encountered a restricted catalyst where the only symptom is a slight decrease in fuel mileage...

every Fuel trim you have posted on this thread is Normal. A 97 K1500 5.7 Gets 11mpg City and 17 hwy. You can't expect to get better then that.

I'm with Noah and doodah, the mixture looks totally fine. Remember that your stft is always going to be bouncing around. It would be more concerning if it wasn't. If the sum of Lt and st is less than + or - 10% I'd shut the hood. If you're looking for a few lost mpgs, consider other factors like ambient temp, tire pressure, dragging brakes, personal weight gain after turkey feast, etc. I work at a dealership and these numbers aren't even unusual for brand new vehicles because there are so many variables.

I agree with Doodah14. I've owned a 98 version of this truck since new and 17 mpg is the best I've ever gotten and that was on a long trip. Most of the time it's about 14 or 15 mpg.