The OBD1 Prelude P14 ECU (for non-VTEC H23A1) and the P13 ECU (for VTEC H22A) share similar circuit board architectures. This guide outlines the hardware modifications required to convert a non-VTEC P14 ECU board to function as a VTEC-capable P13 board.

Hardware Conversion#

Converting the P14 to P13 requires populating missing VTEC driver circuitry and adjusting resistor configurations.

1. Components to Add#

Populate the following unpopulated locations on the P14 circuit board:

• IC11 & IC12: Driver IC (SI5050S/SK) – Solenoid drivers.
• Q35E: MOSFET Transistor (2SK329) – VTEC solenoid driver.
• Q29: Power Transistor (2SD1780) – Power driver.
• IC4: Hex Buffer (74HC365).
• DM1: Diode Array (S233).
• Resistors: Populate R55, R56 (820 $\Omega$), R59, R115 (10k $\Omega$), and R121 (22k $\Omega$).
• Configuration Jumpers: Install J5, RP12, RP16, and RP17 (0 $\Omega$ jumpers).

2. Components to Remove/Modify#

Remove or relocate the following factory P14 components:

• C41: Remove.
• Q30: Remove.
• RP11, RP15, RP18: Remove.
• RP12, RP17: Replace with 0 $\Omega$ jumper.

Verification#

1. Inspect: Use a magnifying glass to check for solder bridges on IC11, IC12, and IC4.
2. Chip the ECU: Install an external ROM socket to support P13 calibration files.
3. Burn ROM: Program an SST 27SF256 EPROM with a stock P13 (H22A) BIN file.
4. Test: Connect the ECU; confirm the CEL illuminates for 2 seconds and turns off upon ignition.

Always verify your board revision before soldering, as minor layout variations may exist between different P14 production batches.