Rear O2 sensors only give emissions readiness and function data for the cats, they have zero effect on the engine.
This looks like another "deleted/desensitized/or knock retard commanded to instantly re-insert max timing for max power w/out the safety the knock sensors provide.
Also could be compounded by past partial hydro-lock that deformed and cracked piston allowing it to be weakened until some detonation took it apart.
F150 Ecoboost, well know questionable tuner that has been defrauding vendors and has a growing list of similar failures.
CAI and a few other bolt ons, but nothing that could contribute to this.
I really need the rest of the piston parts in hand to examine closely and I can tell exactly what happened, so right now is an educated guess, and that is what I describe above.
We have been doing tons of R&D and tear downs of DI engines since 2008 as well as mods and have pushed the limits on WRX, Mazda speed 3's, GM 4L super charged and turbo charged, and all the rest from Audi to Mercedes seeing what limits, failures, and issues all have. The failures of the EB engines to date we see are mainly hydro lock issues and bearing failures due to the contaminated engine oil from the poor PCV system, but the past few months more and more are definately tune related. The knock sensors are there to be a fail safe, so if timing is being pulled as KR, there is a reason for it. Anyone can desensitize or defeat knock sensors and poor the timing advance at an engine and get more power than the next tuner if that is the goal.....but to what end? A good SAFE tune requires intact knock sensors tables with only some minor tweaks and being aware of just how lean is too lean as far as A/F ratio under load and in boost when detonation is most prevalent. If you log your EB and see some KR timing pull that is normal to an extent. If your under a load and at full boost and see no KR, especially if approaching high 13 or 14:1 or leaner, then someone has messed with the sensitivity or worse and your safety is missing.
In the old days before computer controlled engine management we listened for the telltale "marble rattle" (death rattle) and new to back off the timing a few degrees until it was no longer heard (if the pistons did not melt in the meantime). But today, the knock sensors will detect this detonation far faster then the human ear can detect and already command the ECU to pull timing until it ceases. All in milliseconds. These engines we all know have the PCV system design flaw, but that aside, a very skilled tuner will know how to do some minor tweaks to the spark and KR tables to avoid failures like these (nearly always catastrophic) , while the reckless tuner looking for bragging rights will disregard and push for the biggest dyno #'s no matter the cost to the vehicle owner, and then blame engine failures on everything BUT their recklessness.
I'll report back more as we find. We can almost always inspect and study a failure and determine what happened by studying all the parts and determine what happened first, and what the initial failure then caused. Can't hide detonation , it leaves its very bold signature. Hydro-lock (the most common) will show piston top pieces with no signs of erosion or breached piston ring seal, and the rod(s) are always bent to some extent. Contaminated oil will show long term gradual wear of the bearings and journals and a good amount of those particles will be tapped in the oil filter showing the progression before a bearing finally "turns". Heat discoloration on the main and rod caps will show which starved/failed first as the most blue/discolored and it is usually a clear indication from the oil galley feed first in line from the oil pump that will show if metal was circulating (fuel/water/etc. accumulated in the EB crankcase due to the PCV falw...the Caddy ATS L4 turbo has the same issue, just not as severe).
Hope this helps, and understand, ALL with a "reckless" tune will not have engine failure, the use of nothing but 93 octane will be a good safety step, etc. Meth inj is also a great safety step to take.
I would like to see more oil analysis done by members and the results posted. Always take the sample after the engine has been run for a period and is hot, cap the sample as unburnt fuel will quickly evaporate. And I trust BlackStone as a very consistent source to use.
