The attached pic shows a MEMCAL, a MEMCAL with out the blue cover, a PROM and a CALPAK. These pieces are found in GM ECMs.

A single ECM will have either the MEMCAL or the PROM & CALPAK combination.

A MEMCAL contains both a PROM & CALPAK. It will sometimes contain a knock filter (as shown in the picture). The '165 ECMs as used in the TPI f-bodys do not have the white knock filter board.

The CALPAK portion of the MEMCAL is located under the knock filter board.

The PROM contains the software and calibration information for the ECM.

The CALPAK contains the limp mode resistors. These resistors are used to calibrate the redundent fuel device (RFD). This allows the engine to still run when the main ECM processing system fails.

On port injection ECM's the CALAPK also contains a cylinder select function. This allows the ECM to know how often to fire the injectors. Once per revolution for an 8-cyl is every 4 distributor reference pulses (DRP). For a 6-cyl it is every 3 DRPs.

The CALPAK is also known as the NETRES (network of resistors).

The P4 ECMs ('730, '165) use a MEMCAL.

The C3 ECMs ('8746, '7302) use the PROM and CALPAK.

RBob.