Reciprocating Engines (1) Preignition is caused by improper ignition timing. (2) Detonation occurs when an area of the combustion chamber becomes incandescent and ignites the fuel/air mixture in advance of normal timed ignition. Regarding the above statements, a. only No. 1 is true. b. both No. 1 and No. 2 are true. c. neither No. 1 nor No. 2 is true.