Fuel density, vaporization, and combustion efficiency are significantly influenced by coolant and air temperature. The RM-Primis ECU allows fine-tuning fuel delivery based on these conditions using two separate compensation tables:
Purpose: Adjusts fuel injector pulse width based on engine coolant temperature (CLT). When the engine is cold, fuel tends to stick to intake walls and vaporizes poorly. This table compensates by adding extra fuel at lower temperatures to ensure proper combustion.
Coolant Temp (°C)
Injection Compensation (%)
100.0
0.00
90.0
7.91
80.0
9.22
70.0
10.35
60.0
11.82
50.0
13.50
...
...
-40.0
20.32
Actual Value Display:
Temperature: Shows current coolant temperature (e.g., 61.6 °C).
Compensation: Displays the interpolated injector fuel increase percentage currently being applied (e.g., 11.58%).
ROM Controls:
Load: Load a stored CLT compensation map.
Store: Save the current map to ECU memory.
Import Table: Import values from a different tune or configuration file.
Purpose: Compensates for changes in air temperature. Colder air is denser and requires more fuel; warmer air is less dense and needs less fuel. This table allows you to adjust fueling accordingly to maintain a consistent AFR.
Air Temp (°C)
Injection Compensation (%)
100.0
0.00
90.0
0.00
80.0
0.00
70.0
0.00
...
...
-40.0
0.00
⚠️ In this example, the IAT compensation table is flat (0.00%) across all temperatures, meaning no additional fuel is added or removed. Adjustments may be necessary for extreme climates or performance tuning.
Actual Value Display:
Temperature: Shows the current intake air temperature (e.g., 38.4 °C).
Compensation: Current percentage being applied to injector timing (e.g., 0.00%).
ROM Controls:
Load, Store, and Import Table buttons behave the same as in the CLT section.
CLT Comp is most important for cold starts and warm-up. Enrich fuel at low coolant temps, and taper down to 0% at operating temperature (e.g., 85–95°C).
IAT Comp is useful for correcting AFR variations due to seasonal or daily temperature swings. Slight enrichment at cold temps, and lean-out at high temps, can stabilize performance.
Monitor logs to detect AFR drift with temperature changes, and adjust these tables accordingly.
Excessive compensation can result in poor fuel economy or rich misfires—tune carefully and test changes under load.