GM notes that 2008-2019 vehicles, such as Buick Cascada, equipped with a direct injection engine may exhibit black smoke, rough idle and minimal misfires on a cold start. Some customers may also state that the MIL is not illuminated.
With the introduction of direct fuel injection systems, GM has revised the cold start control system to reduce cold start emissions. Quicker catalytic converter heating helps meet the ever-changing emission requirements and improve fuel economy.
A dual-pulse injection strategy is utilized during cold start to reduce the time to bring the catalytic converter up to operating temperature. This dual-pulse injection strategy last for about 60 seconds on cold start. This process will cause the customer to see increased black smoke, soot, rough idle or minimal misfires during cold start and “should be considered normal.”
To verify that the dual-pulse injection is causing the roughness or misfires with no codes set, you should watch injector pulse width with a scan tool during the concern. Dual pulse injector pulse width will be nearly double that of normal idle. After 20 seconds, the pulse width will drop by about 50% and the engine idle will smooth out. This is considered normal operation and no repairs should be attempted.
This cold start strategy is enabled upon start-up after the engine has soaked for sufficient time such that the catalytic converter requires rapid reactivation. The high pressure fuel pump test will run, as soon as the dual pulse injection is completed or during the first stop after the engine is warmed up above about 155 degrees Fahrenheit.
This can feel like a slight idle roughness as the high pressure fuel pump is commanded to max pressure and then shut off to measure pressure decay.