Holden Commodore models from VN to VY (1988-2004) used a Delco Electronics engine management system. They were replaced on V8 models in 1999/2000 (VT S2, VS S3) and on V6 models in 2004 (VZ).

VN / VP used an engine control unit (ECU). Later models introduced electronic transmission control, so the control unit can be referred to as a PCM (Powertrain Control Module). Manual VR / VS vehicles continued to use an ECU.

The ECU / PCM wasn’t vehicle specific. Early models included a “memcal” (memory calibration), which contained the calibration data and software the ECU would run on. This allowed the same hardware to be used in different applications, by only changing the memcal (eg. JE Camira and N13 Pulsar use the same ECU as VN / VP Commodore). The very last models (VX, VY) did away with the memcal, and used reprogrammable flash storage built into the ECU.

There was also RFI (Radio frequency Interference) versions used on police vehicles, which use a metal connector housing instead of the standard colored plastic housing. These are otherwise functionally identical to their equivalent non-RFI ECU.

The label contains the “service number” (which identifies the hardware of the ECU / PCM itself). Units with the same or a compatible service number are interchangeable.

The 4-digit BCC code (broadcast code) identifies the memcal (ie. program and calibration) that was originally fitted to the ECU. Since the memcal is removable, this may have been changed.

Memcals

The memcal is removable, and located within the ECU behind a cover plate.

Early model ECUs with 2 connectors use a “Long” memcal. Later model 3 connector VS and VT PCMs use a “Short” memcal.

Long Memcals

Long memcals contain 2 or 3 main components:

• Memory EPROM
  This is the large main chip that contains the main program and calibration memory for the ECU.
• NetRes
  The 2 smaller NetRes (“Network of Resistor”) chips provide basic hardware configuration for the ECU (such as number of cylinders). It also provides calibration for the backup analog fueling mode.
• Knock Filter
  When a knock sensor was used, this was a separate analog filter circuit located above the NetRes chips.

Short Memcals

Short memcals only contain the memory EPROM chip.

Filtering of the knock sensor signal was handled directly by the PCM, and a NetRes isn’t required to configure the hardware or calibrate a backup analog fueling mode.

EPROM Memory

The EPROM (Erasable Programmable Read-Only Memory) used to store program and calibration varied depending on application. Long memcals used either a 27C128, 27C256 or 27C512. Short memcals used a 27C010.

The BCC (broadcast code) identifies the program and calibration version present on the memory chip. The 4 digit BCC code on the silver sticker would match the BCC code on the ECU label, unless the memcal has been replaced.

Factory memcals used a UV erasable EPROM. The silver sticker covers a quartz window where UV light can be used to erase the memory contents of the chip. You should generally never remove the sticker, as light entering could damage the data inside.

Knock Filters

The knock filter was only used on long memcals. Only V6 models and HSV V8 models used them, standard V8 models did not use a knock sensor. V8 knock filters can be identified by the “1F….” code. Other codes such as “3U….” are V6 knock filters.

If the knock filter (ESC) is enabled in the memcal program, the knock sensor and correct knock filter must be fitted. Otherwise real knock wont be detected, false knock might be, or maximum ignition retard may always be applied.

ALDL

ALDL (Assembly Line Diagnostic Link) is the serial data protocol Delco ECUs use to communicate with scan tools and other modules in the vehicle.

Early VN / VP models used a low speed unidirectional data output on the check-engine light wire, referred to as 160 baud ALDL. It didn’t provide very much data and wasn’t much use, as it was slow and only allowed data out of the ECU.

VR onwards use a bidirectional 8192 baud 5v single wire UART signal, typical of many other US built GM vehicles, and often referred to as OBD1. This allows communication at greater speed, between multiple modules, and both sending and receiving data. VR and VS used it for VATS (Vehicle Anti-Theft System), low speed fan commands to the BCM, as well as scan tool communication.

VT onwards use it to a much greater extent, with every vehicle module (PCM, BCM, Cluster, ABS, SRS etc.) constantly sending and receiving data in a loop known as “bus chatter”. Basic vehicle functions such as controlling the coolant temperature gauge and warning lights operate via ALDL.

Vehicles that used more modern engine controllers (VT onwards LS1 V8, and all VZ models) used a PIM (Powertrain Interface Module), whos purpose was to translate data between the ALDL bus and the modern OBD2 compliant bus of the engine controller (eg. J1850 or CAN).

Tuning a Delco

Tuning and modification of the factory ECU / PCM is possible. Over the years, a lot of community effort has gone into reverse engineering the operation and programs used. Commercial solutions such as Kalmaker also exist.

For an extensively modified vehicle / engine, that requires recalibration to run correctly, check out the pcmhacking.net forums. A copy of most of the factory memcal binary files, and community developed Tunerpro definitions are available. Memcals can be UV erased and re-programmed with an EPROM programmer (such as the XGecu T48). The EPROM chip can also be replaced with an EEPROM to simplify the process, and allow larger program code.

“Real Time” tuning is also possible thanks to custom factory-based code OSE $12P and $11P. A suitable NVRAM will be required for memcal based ECU/PCMs (long or short memcal types), as well as a suitable ALDL communication interface (for VN / VP or VR onwards). There are also enhanced versions of some of the factory code that can be used.

For basic / standard applications, Mr Module can provide a replacement memcal or re-flash your VX/VY PCM. This is ideal for things like:

• VATS anti-theft system disable, to remove the system for an engine conversion.
• Changing cooling fan on/off temperatures.
• Removing / disabling DTC’s (eg. when not using an oxygen sensor).
• RPM limiter changes (eg. for burnout cars).
• etc…