Popol Vuh: Foundational ECU Documentation
An overview of the Popol Vuh project, the foundational documentation effort that served as the catalyst for the Honda ECU tuning community knowledge base.
The Popol Vuh project represents the origin of the centralized Honda ECU documentation effort. Originally compiled as a comprehensive spreadsheet, this data served as the primary technical foundation for mapping Honda engine management systems, sensor data, and diagnostic protocols.
Project Significance
The Popol Vuh dataset provided the initial framework for decoding Honda OBD-0, OBD-1, and OBD-2 ECU architectures. By aggregating pinout data, memory addresses, and sensor scaling factors into a structured format, it enabled the community to transition from proprietary "black box" tuning to open-source diagnostic and modification capabilities.
Note
This documentation serves as a historical reference for the evolution of Honda ECU tuning. For current diagnostic procedures, refer to the specific ECU hardware documentation.
Core Data Components
The original dataset focused on the following technical areas:
- ECU Pinout Mapping: Identification of signal paths for fuel injectors, ignition timing, and sensor inputs.
- Sensor Scaling: Conversion factors for coolant temperature, intake air temperature, and manifold absolute pressure sensors.
- Diagnostic Protocols: Early identification of error code triggers and communication handshakes.
Technical Reference
For users looking to utilize the data derived from these foundational efforts, the following resources are available:
Resistor Color Code Reference
Use the color bands on through-hole resistors to identify their resistance value before installing ECU jumpers, pull-ups, voltage dividers, or sensor-scaling parts.
How to Read the Bands
| Resistor Type | Band 1 | Band 2 | Band 3 | Band 4 | Band 5 |
|---|---|---|---|---|---|
| 4-band | 1st digit | 2nd digit | Multiplier | Tolerance | - |
| 5-band | 1st digit | 2nd digit | 3rd digit | Multiplier | Tolerance |
Color Values
| Color | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | x1 | - |
| Brown | 1 | x10 | +/- 1% |
| Red | 2 | x100 | +/- 2% |
| Orange | 3 | x1,000 | - |
| Yellow | 4 | x10,000 | - |
| Green | 5 | x100,000 | +/- 0.5% |
| Blue | 6 | x1,000,000 | +/- 0.25% |
| Violet | 7 | x10,000,000 | +/- 0.1% |
| Gray | 8 | x100,000,000 | +/- 0.05% |
| White | 9 | x1,000,000,000 | - |
| Gold | - | x0.1 | +/- 5% |
| Silver | - | x0.01 | +/- 10% |
| No band | - | - | +/- 20% |
Common ECU Examples
| Value | 4-Band Code | Typical Use |
|---|---|---|
| 220 ohm | Red, Red, Brown, Gold | LED/current-limiting or ECU hardware mods |
| 1k ohm | Brown, Black, Red, Gold | Pull-up, jumper, and driver-bias circuits |
| 1.2k ohm | Brown, Red, Red, Gold | Driver-bias circuits such as IACV repair references |
| 4.7k ohm | Yellow, Violet, Red, Gold | Transistor base resistor circuits |
| 10k ohm | Brown, Black, Orange, Gold | Pull-up, pull-down, and sensor-divider circuits |
Tip
Always confirm the measured value with a multimeter before soldering. Old ECU resistors can be heat-discolored, and some boards use small surface-mount parts marked with numeric codes instead of color bands.