Why purge depends on temperature
The EVAP system stores fuel vapor from the tank in a charcoal canister, then feeds it into the intake to be burned. That extra fuel arrives unmetered, so the engine has to cope with it. A warm engine with a hot catalytic converter handles it easily. A cold engine and cold cat can't, and the result is a rich, rough running engine and higher emissions.
That's why this table exists. It adjusts the purge solenoid duty according to coolant temperature.
How we fill it in
- At cold coolant temperatures, use large negative corrections. That's normal and expected, and it cuts purge heavily until the engine warms.
- Taper the correction back toward zero as the engine approaches operating temperature.
- At full operating temperature, leave it at or near zero so the main duty tables are in charge.
The table can be made 2D, so you could add a second axis if you want the correction to depend on something else as well.
Log lambda and fuel trims during warm-up. If the mixture goes rich as purge starts, pull more duty out in that temperature range.
The correction works on top of Duty Cycle (O2 Active) and Duty Cycle (O2 Inactive). An accurate coolant reading matters here, such as from a Haltech coolant temp sensor. For wiring, see EVAP Wiring.
