Cars · Wiring
OBD1 ECU ROM Conversion Formulas
Index of scaling formulas for converting raw hex values in OBD1 ECU ROM maps into readable engineering units.
This index provides reference formulas for translating raw hexadecimal values from OBD1 ECU ROM maps into human-readable engineering units. These formulas are necessary for understanding and modifying fuel, ignition, and sensor tables.
Scaling Formula Index
| Parameter | Type | Application |
|---|---|---|
| Low-Cam RPM | 8-Bit | Low-cam fuel/ignition tables, VTEC crossover. |
| High-Cam RPM | 8-Bit | High-cam fuel/ignition tables. |
| RPM (General) | 16-Bit | Rev limiters, target idle, system-wide RPM values. |
| MBar (Pressure) | 8-Bit | Absolute pressure scale used in all fuel/ignition tables. |
| Fuel | 8-Bit | Fuel injection pulse width values. |
| Advance | 8-Bit | Ignition spark timing advance. |
Technical Note
These scaling formulas provide the mathematical foundation used by ROM editor software. When developing custom ROM analysis tools, ensure that your codebase correctly implements the specific bit-depth conversion logic (8-bit vs. 16-bit) to ensure table integrity.