Misfire/overfueling?

[Thumper1311]

Short version:
I'm getting the lovely P0151 bank 2 sensor 1 low voltage O2 code. I originally replaced that exact sensor and the code cleared and it ran normal for a month. Then, same code and problem came back along with idle. Replaced cap, rotor, wires for maintenance purposes and b2s2 for S&G's with no change.

Running conditions:
I have exhaust on the truck (orig headers/cats, just ratty glass packs) so I'm positive I'm only having issues on bank 2. In open loop, it runs fine, as soon as it hits closed loop, I get the choppy idle and even misfires under load. However, its not constant, it comes and goes during each trip. I'll pull up to one light and it runs like crap. I get to the other side of town and it idles smooth, get back home and its spitting and sputtering.

If I'm sitting at a light, a slight RPM change clears the idle out (shifting between N and D)...which is weird.

I'm scratching my head as to what this can be? I feel like the MAF is out since its only a bank 2 issue, and while I COULD buy the crap to clean it, that's just more money thrown at a problem that's not going to fix it. Compression, fuel pressure, valves all seem out because it idles normal and runs fine in open loop. I checked the sensor wire after the plug to see if there was any damage that could be causing a short but it doesn't appear to have any kinks or pinches... I haven't put anything other than a code scanner on it.

I do have a friend who is a long time service manager and he says they have wasted time trying to solve issues like this before, but its usually solved by replacing the dist. cap since they burn out so often. Same thing happens on 4.3's. I can have them put a scope on it, but trying to avoid the cost associated with a shop.

Thanks for any help.

Edit: also checked for vacuum leaks. PLUS my evap canister lines are like...taped on and likely leaking and i don't know how that plays into the truck running, didn't think it had major impacts.

 

[east302]

Here’s the diagnostic table for that code, maybe it will help...

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[RawbDidIt]

Have you pulled the sensor to ensure it isn't getting fouled? Seems odd that it worked, then didn't. If it's not fouled, I'd try making it run a bit rich on purpose, see if it clears the code or throws a new one on three same sensor. You can also check the EGR valve, but that usually throws codes in pairs in my experience. The last thing I'd check would be an exhaust leak.

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[delta_p]

Given you mentioned you checked the fuel pressure, spark, etc. When it runs or idles rough, i might pull over and unplug the MAF and drive. This should throw a P0101 low frequency code. The VCM should begin to calculate the airflow by the IAC valve position, TP position, RPM, and MAP only, and it should run rich. If it still runs crappy or the P0151, then I'd check the IAC and the TP.

 

[1998SSLT]

I had same codesc and issue with a 98 5.7 the old style spider injection was fouling a couple cylinders. It ended washing those cylinders down and took out the engine.