Converting the OBD1 P14 ECU to P13 (H23A to H22A)
Step-by-step component conversion guide to hardware-modify a non-VTEC OBD1 P14 ECU to function identically to a VTEC P13 ECU.
Adapted from pgmfi.org wiki
The OBD1 Honda Prelude Si P14 ECU (non-VTEC H23A1 engine) and the Prelude VTEC P13 ECU (H22A engine) share similar internal board designs. However, the P14 lacks the VTEC solenoid high-current driver circuit, knock sensor components, and specific resistor configurations required to run H22A calibrations.
By soldering in the missing components and removing or relocating specific resistors, a P14-Q00 board can be modified to be electrically identical to a P13-N01. This allows it to run a stock or tuned P13 ROM.
1. Components to Add
Populate the following unpopulated locations on the P14 circuit board:
| Location | Component Type | Value / Specification | Function / Notes |
|---|---|---|---|
| IC11 & IC12 | Driver IC | SI5050S (or SK) | Solenoid driver control chips. |
| Q35E | MOSFET Transistor | 2SK329 (AIL 4L) | VTEC engagement driver transistor. |
| Q29 | Power Transistor | 2SD1780 (D1780) | Power output driver. |
| IC4 | Buffer IC | 74HC365 | Hex buffer/line driver. |
| DM1 | Diode Array | S233 | Transient protection array. |
| D4 | Diode | Standard rectifier | Reverse voltage protection. |
| C43 | Tantalum Capacitor | 1 uF, 35V |
Filtering capacitor. |
| C42 | Ceramic Capacitor | 103Z (10nF) |
Noise filtering. |
| C77 & C78 | Ceramic Capacitor | 22 pF |
Crystal oscillator filtering. |
| R55 & R56 | Resistor | 820 $\Omega$ | Gate pull-up/pull-down resistors. |
| R59 | Resistor | 10k $\Omega$ | Bias resistor. |
| R115 | Resistor | 10k $\Omega$ | Bias resistor. |
| R121 | Resistor | 22k $\Omega$ | Bias resistor. |
| NF3 & NF4 | Noise Filter | Ferrite beads | High-frequency noise filters. |
| J5 | Jumper | 0 $\Omega$ wire | Solder bridge connection. |
| RP12 | Resistor | 0 $\Omega$ (Jumper) | Configuration jumper. |
| RP16 | Resistor | 0 $\Omega$ (Jumper) | Configuration jumper. |
| RP17 | Resistor | 0 $\Omega$ (Jumper) | Configuration jumper. |
2. Components to Remove
Desolder and remove the following factory P14 components to match the P13 layout:
| Location | Component Type | Original P14 Value | Action / Note |
|---|---|---|---|
C41 |
Tantalum Capacitor | 3.3 uF, 16V |
Remove entirely. |
Q30 |
Power Transistor | 2SD1780 (D1780) | Remove entirely. |
| RP11 | Resistor | 4.7k $\Omega$ | Remove entirely. |
| RP12 | Resistor | 1.5k $\Omega$ | Remove and replace with 0 $\Omega$ jumper. |
| RP15 | Jumper | 0 $\Omega$ (Jumper) | Remove entirely. |
| RP17 | Resistor | 4.7k $\Omega$ | Remove and replace with 0 $\Omega$ jumper. |
| RP18 | Resistor | 4.7k $\Omega$ | Remove entirely. |
3. Post-Conversion Verification
After completing the soldering work:
- Check for Bridges: Use a magnifying glass to verify that the pins on
IC11,IC12,IC4, and the transistors are free of solder bridges. - Socket the Board: If not already socketed, chip the ECU to accept an external ROM (see ECU Chipping Guide).
- Burn the ROM: Burn a stock P13 H22A calibration BIN file onto an SST
27SF256EPROM and insert it into the socket. - Diagnostic Test: Plug the converted ECU into the vehicle. Turn the ignition key to the ON position and confirm the check engine light (CEL) illuminates for 2 seconds and turns off. If the CEL stays solid, verify the EPROM is burned correctly and double-check your desoldered resistor locations.
Credits and source
Authors blundar, speed_of_bokchoy
Source Adapted from P14 To P13 on pgmfi.org wiki. Licensed under CC BY-NC-SA 1.0.