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this applies to some 92+ and most 94+ ecu's excluding the newer variable cam timing ecu's, this DOES NOT APPLY TO THE OLDER GUF ECU'S
at any given time the actual spark delivered is the lowest spark the ecu calculates
idle (feedback) spark is calculated from the mbt
using the torque limiting function fn799
from the following scalars
spk_load_res - feedback spark desired torque
after fbs_entry_tc - feedback spark entry time constant
which is clipped by spk_fbs_min - feedback spark min
and oscillated by spk_fbs_gain - feedback spark gain
not to exceed tr_delta - feedback spark torque ratio max delta
the mbt spark table fn2300 is modified
by the adder for lambse function fn730
the adder for egr function fn731
and the adder for vs fn743
now you can't get into idle feedback spark unless both the idle flag and the closed throttle flags are set, which is going to be primarily due to the IDLRPM scalar and its hysteresis, just make sure your idle air is dialed in and the idlrpm scalar has been adjusted correctly and all should be well
base spark, the sealevel fn2100 and altitude fn2110 tables are modified by:
ect fn2120
lambse fn2140
egr fn711
and bp bias fn712
for ease of keeping track of timing many folks just set the base tables high, say 60, ecu uses lowest calc'd spark
borderline knock is the most used table as it has the most inputs for knock suppression, the borderline knock table is what i use and recommend everyone else to as well
the borderline knock table fn220 is modified by the following which are sub-modified as noted:
act fn2230 sub-modified by fn725a
lambse fn2240
ect fn2220 sub-mod by fn724a
transient load fn2250 sub-mod by the lug timer fn723
egr fn721
bp fn722
for example: lets say your idling at 750rpm @ 16 load, looking in the mbt table we get an interpolated value of ~33 degrees, the scalar spk_load_res is set to .9 which is the torque ratio from mbt the ecu is demanding, it references fn799 spark mbt retard for torque limiting to see how much to adjust the mbt spark to get its desired tq ratio, lets say .9 = -15 in the fn799 function, this gives us an idle spark of 18
be careful with the spark mbt table fn2300 as thats how torque modulation is referenced to variate transmission tv pressure on ecu controlled automatic trans equipped vehicles
which is no biggie as most folks tend to disable torque modulation anywho
again, the ecu uses the lowest calc'd spark
fn741 is the low load limit spark used when air mass is
below the stab_lold_am scalar, most set this function high if
not already done in the stock cal to null it
tip in retard yanks timing when the throttle is opened beyond the scalar
kacrat - tip in throttle position
which can be disabled by maxing it out ~5.1v or 1023 ad counts
else the tip_min_spk scalar is the minimum spark demanded WHEN a tip in has occurred, not how many degrees to retard as many think, you can set this to 60 to null tip in retard if you don't have kacrat available in your def file
you then have your global spark modifiers like:
spk_add - usually 0
spk_mul - multiplier usually 1
spuclp - max spark clip usually 50 or so
splclp - min spark clip usually 0
later on you then have individual cylinder spark control
also keep in mind the mbt retard limiter function fn799
and spark derived torque ration fn766 should mirror each other
spark oscillation modulation is a steady state spark modifier to aid in stabilizing the current rpm, the SOM table fn2020 is modified by fn746 and fn745, i recommend setting the SOM table to 0
if i didn't make enough of this clear just LMK and i'll elaborate
Last edited by decipha on Sun Apr 10, 2011 2:25 pm, edited 1 time in total.
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