A. these are mass produced engines, rotating assembly's have been found to be 7 grams out of balance due to "gross" balancing of engines and parts bins.
B. production differences are massive, damn close for 100,000+ units...but ****ty. head castings with port obstructions, cams with lobe lift all over the place as the grinding wheel wears...
C. carbon buildup in the chamber/ports, injector wear and tear on top of a fairly large variance, oil past cyl 4 rings (the cyl4 windage tray issue), pcv recirculation of oil vapor as the rings wear (not like they gapped em) but more than that the wear is inconsistent, similar mile 3800's and i get over 8thou diff on the ring gaps at nearly 100k the cam is nearly 2* retarded with the chain/sprocket wear.
D. SENSOR production tolerances/wear/skewing, NB O2's, MAF. buildup of crap on "trusted" sensors, skews readings and changes fueling.
all this is why you ended up with some factory freaks, and some factory dogs.
i dealt with a factory dog, 02 gt, knocked na, knocked sc'd, even with headers, exhaust, intake and me porting the new heads...still knocked.
changed out the shortblock to a different NA shortblock (98)
KR gone, no changes to tune, only thing changed was the shortblock, reused the 02 KR sensors as a test of my theory. OE L36 kr sensor tq.
sometimes yer just ****ed.
but i heavily agree people run em too rich. its horrible to see a low mile motor with polished bores and no crosshatch to be seen.
