This thread has kind of morphed from the original intent I had when starting it...and that's ok. I also feel a bit of a need to collect all the relative details together in a bit of a summary as it feels a little frayed at the moment, largely at my own fault.
Ok, so, 2008 Yukon Denali, 200+k miles. I purchased it in mid March, '18. It ran ok, but not great, but I got it for a LOW price so I was ok with having to address some things. First thing is it was setting a P0455 EVAP leak code, fouling the plugs, and had a pronounced miss/stumble around 1500-2000rpm. So, in my efforts to address the EVAP issue, I ended up replacing the entirety of the EVAP system. Gas cap, Vent Valve solenoid, EVAP canister, purge valve, and the fuel pump assembly with an OE Bosh unit. EVAP issue solved. Next order of business were fresh wires (AC Delco) and plugs (NGK Iridiums). Around this same time I picked up a Diablo Sport i3 crazy cheap. I know a good tune from a reputable shop is better, not wanting to start a debate on that. Again, I picked it up really cheap and it gave me something to play with and tweak with. I had also by this point run about 2-3 cans of Seafoam and 3-4 bottles of Techron through the fuel system, and done one Seafoam oil treatment. Now, it ran pretty good at this point, but still would detonate audibly at WOT and occasionally under part throttle heavy load. This was on the stock tune. On the Diablo tune it would do it more severely, but outside of WOT and part throttle heavy load ran GREAT. I always run 93 from a name brand (usually top tier rated) station. So, at this point since it would detonate even on the stock tune I began my train of though I referenced in my above response. That it had to be due to lack of fuel, or maybe severe carbon build up. High miles, no clue how the previous owners drove it, nor the quality of fuel used. I figured the carbon build up wasn't likely anymore since I had run a fair amount of Seafoam and Techron through it. So, I had been leaning more towards lack of fuel, maybe either caused by tired, worn out original injectors, or after seeing a few mentions about lazy O2 sensors causing some problems, that. As mentioned earlier, I have two new upstream sensors ready to install once the weather cooperates, which hopefully will be this weekend. Now, in another thread on here I had seen someone mention an engine/fuel system cleaner called Kreen by Kano Labs which many people were swearing by. I began reading up on this stuff across various forums and in the process of that saw frequent mention also of Berryman B-12 Chemtool fuel system cleaner, and that it was considerably better than Seafoam (but not as aggressive as Kreen). Kreen is mail order only, and since the B-12 stuff was locally available, while traveling out of town for Christmas I ran a can of it through the fuel system, honestly not expecting much. However, after running a single full can of it, I have ZERO detonation under any condition on the stock tune now. It's still there in the same places on the Diablo tune, but completely gone on the stock tune. This makes me think that perhaps one of the contributing factors was indeed just severe carbon build up or other fuel system deposits. A friend of a friend actually runs an injector clean/flow/rebuild business so here in the next couple of months I'm probably going to pull the injectors and get him to bench clean and rebuild them. I'll probably run another can of the B-12 through it soon, and maybe order some of the Kreen. After I throw the new O2's in this weekend, since that will now be eliminated from the equation, I'm going to throw the Diablo tune back in it, see if I still have the detonation, and if so start doing a bunch of data logging and tweaking on the tune. With the i3 Diablo Sport you can adjust not only the injector slope but also the PE value.....so if I'm maybe still picking up some detonation from not enough fuel/lean condition, I can play with the injector slope and PE values to throw a little more fuel at it to see if it helps. The stock L92 injectors are 31lb/hr units and supposedly more than adequate, so if it's not getting enough fuel then it has to be just worn out injectors or a fuel pressure issue since I've already replaced the fuel pump with a new Bosch unit and eliminated that possibility.
So, I know that's a lot of random info to digest all at once, but as I said I felt as though at least my part of this thread had started to get a bit scattered and in the spirit of someone finding the thread at some point in the future fighting their own issue, I didn't want there to be any missing points of information that could potentially factor into the big picture.
