OBD1 8-Bit Fuel Calculation Reference
Technical reference for calculating fuel pulse width and duty cycle using 8-bit ROM table values in Honda OBD1 engine management systems.
In Honda OBD1 ROM editors, fuel table values are stored as 8-bit integers. To interpret these values into meaningful fuel metrics, use the following mathematical conversions.
Fuel Value Calculation
Given a table value v and a multiplier m, the fuel value is calculated as:
Fuel(v, m) = (v * m) / 4
The resulting value is proportional to the fuel mass entering the engine, with an effective range of 0â16256.25.
Pulse Width and Duty Cycle
To determine the relationship between the ROM table value and injector performance, use the following formulas:
Pulse Width (PW)
PW (ms) = (v * m) / 400 + 0.60ms
Duty Cycle
Duty Cycle = (RPM * (v * m + 240)) / 24,000,000
Important
These formulas are derived from empirical data and represent theoretical calculations. Always verify fuel delivery and injector duty cycle using real-time data logging and wideband oxygen sensor feedback.
Note
The constant 0.60ms in the pulse width formula accounts for injector latency (dead time). This value may vary depending on the specific injector hardware installed.