How to Simplify Timing on the Foxbody ECU
by Michael Decipha Ponthieux
Last updated: 4-23-2013
This page is for the GUFB ecu's only.
The foxbody ecu's have 3 primary spark tables, the base table, sealevel table, and altitidue table. It was often common practice
to set all 3 tables to the same values, this does work fine, however, it requires you to adjust all 3 tables each time
you make an ajustment to timing which can be tedious.
Disable Base Spark Table
The base table is the lugging table, it can be disabled by setting the lug load function FN125 to all 0 Load.
Disable Altitude Spark
One can now disable the altitude table, this leaves just the sealevel spark table as the only remaining primary spark table.
The memory location to disable the altitude table is:
0x3713-0x3714 [+0x2000 intel offset] opcode DECIMAL: 484 (stock) to 404
Disable WOT Spark Functions
Sometime in the early 90s Henry stopped using the WOT spark functions and for good reason. Using load as the input for spark
gives much more control and efficiency in spark control. By also referencing load you get a 'ramping' effect on spark.
You also gain control of additional engine modifications without requiring adjustment.
The memory location to disable the WOT functions is:
0x36A1-0x36A2 [+0x2000 intel offset] opcode DECIMAL: 18720 (stock) to 53296
Sealevel Spark Table
If you have disabled the wot functions, altitude spark table, and the base spark table, you are now ONLY using the
sealevel spark table as the primary spark table. Populate this table with values that pertain to your setup.
CLICK HERE for the MBT Reference Chart
Now that you only only have the Sealevel spark table remaining, I recommend you null out (set to all 0s) your EGR spark
adder table FN1121 (which can ALWAYS be active when EGR is active) so you get exactly what you demand.
For ACT retard, you will have to populate your ACT spark function FN126, I HIGHLY recommend to NEVER allow the ACT spark
function to add timing only retard timing so your values in your sealevel table represents the absolute maximum spark you will
ever receive. Keep in mind your ACT retard will differentiate between the ACT being mounted in the manifold and the ACT in
the inlet piping. Typically one might retard timing after ACT's reach 100 degrees for inlet piping, and 180 degrees for manifold
NOTE: If using the A9L2 Base Calibration, FN126 has been changed to be ECT spark retard instead of ACT.
For ECT retard, you will have to populate your ECT spark table FN1133, I HIGHLY recommend to NEVER allow the ECT spark function
to add timing only retard timing so your values in your sealevel table represents the absolute maximum spark you will ever receive.
For ECT retard, I typically rescale the table and demand 0 at 224 and -4 at 234
NOTE: If using the A9L2 Base Calibration, FN1133 has been changed to ACT spark retard instead of ECT.
Special thanks goes out to Derek Fenwick a.k.a. "sailorbob" for finding these variables in the binary and sharing his knowledge.
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