Not even true, Buddy, which erroneous posting makes it difficult for some to grasp the truth - to wit:
BASE timing is the most retarded position of the camring\Optical Sensor, limited to and set by the physical position of the IP
ACTUAL timing is the measured position of the camring\Optical Sensor while the engine is running, and is variable to match rpm and loading requirements
DESIRED timing is the amount of advance PCM has determined as required to match rpm and loading requirements
DESIRED and ACTUAL timing should always match within a degree or so
+3.5* oem or +8.5* performance Base timing is resulted from the locked-down-by-three-12point-nuts physical position of the IP on the timing cover - PCM cannot change or alter BASE timing, but can DESIRE timing that is advanced wrt Base timing
When TIME SET is commanded PCM first sets idle rpm to 1000rpm to prevent the engine dying during timing procedures, disables DESIRED timing advance, using 0 advance to move the camring to it's most retarded position, then wratchets the Timing Stepper Motor to rotate the camring\Optical Sensor between the physical limits set by the current location of the IP, comparing that range of movement to crank TDC - PCM is measuring the available range of advance in degrees at that position - camring\Optical Sensor rotation is limited to 22* total by the design of the advance piston, which gives 11* total advance at crankshaft - minimum timing position with 0* advance is actual BASE timing, or +3.5*BTDC crank, with total advance at that position of 14.5*BTDC - rotate the IP ~2mm in the advance direction adds +5* for +8.5* actual BASE timing, with max advance of +19.5*BTDC - PCM never commands, and the IP cannot respond to, negative advance, or retard, below actual BASE timing - 'nuther words, it cannot go below actual BASE timing value .......unless the IP was mistakenly retarded to some degree less than oem minimum of +3.5*
Once PCM determines IP position in *BTDC during TIMESET, it wratchets the stepper to move the camring into BASE timing position, again, determined by the physical position of the IP - that position is actual BASE timing with 0* desired advance - OBD1 can read this number, OBD2 fudges the +3.5* number to fake out any enquiring minds, in accordance with the FSM blurb on timing alteration and performance gains - when TIMESET is de-commisioned, PCM resumes normal timing operation - now, you're setup do TDCO LEARN
Next, when TDCO LEARN is commanded, and here's where OBD2 KOKO comes from, PCM once again dials in 1000rpm, sets DESIRED (advance) to 0 to fully retard the camring\OS for starting position, wratchets the TSM thru min to max timing, prolly verifying what was measured in TIMESET, then moves the camring\optic sensor back to actual BASE timing position with 0 advance - PCM then computes a Top Dead Center Offset based on that measured range - now, altho PCM has disabled DESIRED timing function display in TDCO LEARN, as engine rpm is increased PCM calls for, or DESIRES, timing advance as required to match the increased rpm - this hidden advance is where the range of TDCO values for each actual base timing setting comes from: PCM continually recalculates TDCO based on the varying advance required for the varying rpm as if that were the actual BASE timing - so, you get a range of values for each actual BASE timing position: at +8.5*BTDC you can get -1.5* to -1.94* TDCO while in TDCO LEARN merely by increasing engine rpm until you see the desired value (pun intended, snicker!), then exit TDCO LEARN to lock that value into PCM
OBD2 KOKO procedure takes advantage of the positional advance remeasuring (TIMESET) that TDCO LEARN goes thru prior to calculating the correct TDCO value - thus, you don't need TIMESET in OBD2
And, that's how it really works, folks, word up.................
