• Add all bytes in the EPROM, starting immediately after the Checksum word itself.
• Truncate the result to 16 bits (4 hex digits).
• 
  The result is the checksum.

• Add all bytes starting at relative address $0002 and continuing to the end of the EPROM, ($0616).
• The result was found to be 72,182 decimal, or $123456.
• 
  Truncating the result to 4 hex digits results in $3456, the new checksum.

In some ECM's several different software variations (different ID byte), may be in use although the ECM service number is the same.

If the value $AA is stored here then the ECM does not perform a checksum test, This is considered the engineering code.

The Main Spark Table is a 3D table is organized as a 14 row by 15 column tables as shown below

There is a three byte header that define the minimum RPM value, minimum Map Value and the number of rows in each column. 

The total spark applied to the engine is the summation of several values, this table is the base value. 

The value to store in the table is the retard in degrees, multiplied by 5.688 (256/45)  To use12 degrees of knock retard do: 12 x (256/45) = 68, or $44.

Same as the RPM table above only this table is MAP selected.

Accelerator pump enrichment TBI systems  needs to emulate the accelerator pump found on carburated engines. The accelerator pump on a Carburetor injects a big squirt of fuel into the manifold when the throttle is opened quickly. There are three reasons for this extra fuel in that case of a Carburated engine.:

1. The sudden opening of the throttle lets in more air, which the ventures can't immediately respond to.
2. The sudden opening of the throttle increases the absolute pressure in the manifold, which can cause some of the vaporized gas to condense into a liquid on the manifold walls.
3. At WOT you want more fuel anyway to make the most power.

The TBI system has a slightly different problem, since it can react to rapid opening and it has a TPS sensor to tell the CPU about that fact, and we don't need all that mush fuel at WOT, because we can control fuel much better than a Carburetor.

The TBI suffers from the long delay from the time fuel is called for by the CPU and the time it combusts and ultimately become an o2 signal in the exhaust at the o2 sensor. This is called "transport time".

The type $42 code running in the 1227747 ECM uses the following  two tables to provide acceleration enrichment. 

This table uses change in MAP from one cycle of the ECM to the next as Differential MAP.

Note:
 Address $030D is an eight bit value defining a 5 line table.

This tables specifies spark advance added to the total spark value at (or near)  WOT. When modifying remember that it's better to start with too much fuel and too little spark, and slowly sneak up on better values.

Note:
    $015D Is a one byte value limiting the maximum RPM to 3600 for this table.

This is the main 3D fuel delivery table and its companion 2D table  The value in the table is volumetric efficiency, which is used ultimately in the fuel calculation to determine the injector pulse width along with RPM, and coolant temperature, This is why this is a speed/density system.

Fuel is the easiest parameter to get right, record the Block Learn Value when the Integrator if neutral  (Near 128). Divide the BLM value by 128 and you have the current error from 14.7:1 AFR.

Example:

At 2000 RPM and 50 Kpa:
BLM  = 140
140/128 = 1.09, a 9% error in the lean side 

What this indicates is that the BLM is multiplying the calculated value of fuel by 1.09 to achieve 14.7:1 AFR (The Stocheometric point)

To improve this situation got to 200 RPM and 50 KPA map on the fuel table and multiply the value of VE by 1.09, (46 x 50.14), we round to 50 and move on.

Make sure the total of the two table is less that 100.

Sample table from a stock 5.7l truck.

Volumetric efficiency is expressed as a percentage, the theoretical amount of air that the engine should be pumping at a given RPM divided by the actual amount of air that the engine is pumping

Note:
The VE value used is the result of both table summed. Summed values exceeding 100% will be limited to 100%

These values are used in open loop while cranking.
 

Controls idle speed based on engine temperature until the Idle speed PID loop can get control of idle RPM. see Idle RPM Vs. Coolant
 

These values are used during open loop operation
 

Disabling a code does not necessarily turn off the corresponding test. It does prevent a failure code from being stored and prevents the check engine light from coming on.

Each address has an 8 bit value stored, and each bit controls a particular diagnostic code. 

Example:  $050D has the value $FC. (1111 1100 in binary). The two zeros are in the LSB (least significant  bit) (b0 & b1), that means codes 24 and 23 are disabled.
 

          bit 0   code 24, VSS 
          bit 1   code 23, MAT Sensor low temp, (Not Used)
          bit 2   code 22, TPS low
          bit 3   code 21, TPS hi

          bit 4   code 15, Coolant sensor low
          bit 5   code 14, Coolant Sensor Hi
          bit 6   code 13, o2 sensor 
          bit 7   code 12, No ref's, (engine not running ?)
 

           1  b0  code 42, EST Mon error 
           0  b1  code 41, NO DRP , (Not Used)
           0  b2  code 35, IAC ERROR, (Not Used)
           1  b3  code 34, MAP Sensor low

           1  b4  code 33, MAP Sensor hi
           1  b5  code 32, EGR failure
           0  b6  code 31, MAP LOW, (Not Used)
           0  b7  code 25, MAT Sensor high temp, (Not Used)

           1  bit 0  code 55, ADU Error
           0  bit 1  code 54, Fuel pump relay malfunction
           0  bit 2  code 53, VATS, (Not Used)
           1  bit 3  code 52, Cal-pack missing

           1  bit 4  code 51, EPROM error
           1  bit 5  code 45, o2 Rich
           1  bit 6  code 44, o2 Lean
           1  bit 7  code 43, ESC failure