I like to start by knowing if there's fire. With an inductive timing light clip to each plug wire, crank engine check for light pulses. check each wire in succession. Hope this low tech approach helps.
Good Luck
Steve

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Steve Short
'91 300SE sold
'92 190E 2.3 sold
'99 S420
'06 Mini Cooper S
'08 Triumph Rocket III
'02 CLK430