I understand what you mean, we all like to play with new toys
The only advice i could give you in conjunction in using the 2104 on Automotive Applications, not T&M Applications as this isnt really our field, is to keep to circuits under 20 Volts as this is the limit of the Scope.
Definatley Ignition is a complete No go
Potentially you would 'probably' be safe with most battery circuits and engine circuits i.e. 5 - 12 volt stuff but keep away from actuators especially solenoid types. Although these run on the back of Battery Voltage, Injectors for example can get a kick back anywhere upto 125 Volts [MODERN Petrol Injectors] which even out ranges the 4000 Series scopes so you really do risk severe damage to the scope.
Id stick really to simple voltage tests and waveforms where you know the voltages including any kick back voltage wont exceed 20 Volts, this will be limited. Check always if possible the OEM's Technical Information for voltage information to find whats safe to test.
Hope this helps give you an idea what you may do, but if in doubt, you can alway use a Multimeter to check voltage before using the scope but in cases such as Injectors, ISCV's you may not see the kick back voltage as its a fast signal and the Multimeter may not catch it so you still have to be cautious and if still in doubt, dont test it as you have no attenuation to protect the scope.
You will also find the detail potentially poor due to the 8 bit resolution of the scope and the difficulty in grounding due to the way the 2104 works but if you stick to the signals mentioned you may get enough as a study but more than likely not ood enough for diagnostic quality.
I do stress, you must be careful what you test as this scope really isnt designed for use with Automotive Applications and really should not be used for this.