One of the best things i can recommend is to use magnetic coupling of the signals where the amplitude would otherwise exceed the spec of the scopes front end, ignition systems are rarely operating fast enough that you can not get most of the required time based information from wrapping a wire around a current carrying wire then measuring across its ends with a scope, (A large number of scopes can only take 400V peak - peak up to a few dozen Khz)
also, 2 minimum, when your trying to figure out what segment of a system is playing up, being able to easily compare to the previous stage's output can quickly resolve where a fault is originating,