dude I'm not going to argue if you think your right whatever. i'm a licensed tech and my jeep doesn't have variable valve timing or spark timing the only adjustments the pcm in my 95 yj has is fuel timing and length of timing. That's it. Honda "vtec" and other manufactures in newer engines have variable valve timing and spark timing. you can't control spark timing in a distributor unless you move it or have some kind of mechanical advance built in to the distributor witch my yj doesn't. if the pcm changed the spark timing it would make no difference due to the rotor isn't in contact with the distributor cap prongs. the coil can't discharge the energy unless it has somewhere to go. In terms it would short out the coil.
dude, first off i am saying the same thing regarding the inability of adjusting the timing by moving the distributor, so there's no point in an argument there, but read my post again and you'll see that's what i meant (including the quote from you to which i replied - here it is:
Timing isn't controlled by the distributor.
yes it is. why do you think people with performance v8's advance the distributor for more high end output and they call it advancing the timing!!!
they also had centrifugal weights in the older distributors to advance timing at higher rpm!!
if you don't believe me take the distributor out and try to move the rotor while holding the gear - it will not move. Now do the same on a points one and it will move - the ignition advance will vary even though the position of the rotor will not change in relation to the TDC of the cylinders it fires the spark to, so when you have 10 deg advance in timing the rotor won't move forward 5 degrees to compensate.
if the pcm changed the spark timing it would make no difference due to the rotor isn't in contact with the distributor cap prongs. the coil can't discharge the energy unless it has somewhere to go. In terms it would short out the coil.
the rotor is never in the contact with the prongs, and no it will not short out the coil, you can test that by removing the wire from the coil to the center of the dist cap, crank the engine and see what happens, then put it back on and it will start with no problems.
Anyway, whatever (like you said), i'll quit trying to explain since you are a certified tech and we are not.
EDIT: It is explained even in the Jeep Factory Service Manual that you can download from the FAQ section on this site
under general information of the fuel system (page 19 in file 95xj_14.pdf) you can find this
"The PCM is a preprogrammed, dual microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission control devices, charging system, speed control, air conditioning compressor clutch engagement and idle speed. The PCM can adapt its programming to meet
changing operating conditions"and also this right under the one above
Powertrain Control Module (PCM) Inputs represent the instantaneous engine operating conditions. Air-fuel mixture and ignition timing calibrations for various driving and atmospheric conditions are preprogrammed into the PCM. The PCM monitors and analyzes various inputs. It then computes engine fuel and ignition timing requirements based on these inputs. Fuel delivery control and ignition timing will then be adjusted accordingly"on page 31 in file 95xj_14.pdf, section Fuel system component description/System operation - under the engine startup mode section it states
"The PCM determines the proper ignition timing according to input received from the crankshaft position sensor" under engine warm-up mode you'll also find this
"˛ The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing"and on the next page (page 32 in the same file) it says
"The PCM adjusts ignition timing by increasing and decreasing spark advance" and further down under cruise mode
"The PCM adjusts ignition timing by turning the ground path to the coil on and off"- i believe the official service manual to be correct (and it is the same for most modern engines, not just for Jeeps). copy/paste from the manual below
