The effects of ambient temperature, amount of liquefied petroleum gas (LPG) injected per cycle, injection timing of LPG, ignition timing and the electric battery voltage on firing performance, and hydrocarbon (HC) emissions from the first cycle of an electronically controlled inlet port LPG injection spark-ignition (SI) engine were investigated during cold start by means of a cycle-by-cycle control strategy. The results indicated that the amount of LPG injected per cycle is the key factor to ensure the first firing cycle of the LPG engine during cold start; a proper amount of injected LPG makes a reliable start of the LPG engine. The effect of ambient temperature on the minimum amount of injected LPG required for firing is relatively small. If the amount of injected LPG and injection timing of LPG are controlled reasonably to ensure all of the fuel-air mixture to enter the cylinder on time, it is possible to realize the ideal firing in the same cycle with LPG injection during engine cold start, Optimal control of injection timing of LPG and ignition timing improves firing performance and reduces HC emissions during cold start. Increasing the electric battery voltage raises the maximum instantaneous cranking speed and reduces HC emissions from the LPG engine during cold start.