Reading a low voltage signal from a battery connected to a transformer
You probably won’t be able to measure this without extraordinary skills at EMI proofing everything. The arc current rise time will be in excess of 1GHz BW and this means you need RF experience to make a  current shunt with 50 Ohm coax and 50 Ohm terminators with shielding and filtering on all I/O lines and semi-rigid or microwave coax.

Basically the air coil used in igniters has an inductance which ramps current up at a rate of dI=V/L*dt so your pulse width controls the peak current. Then when released the voltage rises to V=LI/dt with dt being very small in xx nsec due to stray capacitance.  When the air ionizes and arcs that same current now collapses from 1kV/mm (sharp point) with a negative resistance in sub-nanosecond times with ringing. When your wire has 10nH/cm this magnetic impulse induces a high  voltage magnetic field that resets your uC. 

My furnace igniter can draw a 2cm arc easily which puts that around 20kV.  The current could be reduced with 20kOhm car spark plug wire and still ignite but the flame would burn the carbon wire and insulation.

If you are having ignition problems it isn’t the current that ignites it but the voltage necessary to draw an arc in the path of the natural gas flow with air mix.  So I would want to know a lot more about your igniter design.  Cars need about 30kV so that a 22 thou gap  at 8 atmospheres of piston pressure to create an arc with (0.55mm gap ) and  breakdown now increased to about > 30kV/mm when cold.

Advice

If you use a low side current shunt for 100mV max current and use an INA diff amp with gain next to battery current shunt and all impulse generation shielded from this circuit, you may see more accurate results. But you need to isolate this arc current from inductive coupling into your board  with balanced signals and shielding.