What is the additional fuel the PCM commands during open-loop startup?

• A. Afterstart Enrichment
• B. Afterstart Decay
• C. Cold Delay
• D. Warm-Up Fuel

Answer: (A)

During startup, the engine isn’t yet operating in closed-loop control because the O2 sensors aren’t ready and the engine is cold. To ensure a reliable start and a quick, smooth warm-up, the PCM adds extra fuel in a preset amount. This specific added fuel is called afterstart enrichment. It is applied during cranking and right after the engine starts, while feedback from sensors isn’t available, so the system can’t rely on closed-loop adjustments yet. As the engine warms and sensors come online, that enrichment is reduced and the system transitions to normal operation or other fuel strategies.

The other terms describe different aspects: afterstart decay is the process of the enrichment fading away after startup, not the enrichment itself. Cold delay isn’t the standard term used for the startup fuel strategy. Warm-up fuel is used during the later warm-up period, not the initial open-loop startup enrichment.