The PR4 ECU is the standard OBD1 engine control unit used in the 1992–1993 Acura Integra RS, LS, and GS models equipped with the 1.8L non-VTEC B18A1 engine.

Note

Acura also utilized a PR4 ECU in the 1990–1991 Integra models. These early units are OBD0. If you are modifying a 1990–1991 unit, refer to the OBD0 PR40 documentation.

Board Layout and Chipping#

The OBD1 PR4 shares a hardware architecture with other OBD1 Honda/Acura ECUs, such as the P28 or P75. It can be modified using standard OBD1 chipping kits to accept custom ROMs.

To chip an OBD1 PR4 ECU, the following components must be populated:

• 28-Pin Socket (IC3): For the custom EPROM/EEPROM chip.
• 74HC373 Latch (IC4): For address demultiplexing.
• Resistor R54 (1k ohm): Enables external memory addressing (or a jumper wire, depending on board revision).
• Capacitors C1 and C2 (0.1 uF): For noise filtering on the latch and ROM lines.

Hardware Visuals#

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Technical Specifications#

Important

Ensure the 74HC373 latch is oriented correctly according to the PCB silkscreen. Incorrect orientation will result in a "Check Engine Light" (CEL) and a non-starting vehicle.