Abstract: An ignition system interface for interposing an automotive combustion engine having a computer controlled ignition with an engine test analyzer. The interface receives timing signals from the ignition computer and generates modified timing based on command from the engine analyzer. Modified timing signals are transmitted to the coil ignition module which fires the spark plugs of the engine. The analyzer may command a shorting of the cylinder which causes the interface to modify the timing at the appropriate time for inhibiting a selected cylinder from firing. Secondary signals from the spark plugs are received by the interface and converted to a proper voltage waveform for recognition by the engine analyzer. The cylinder No. 1 is monitored by the interface and converted to a proper waveform for transmission to the analyzer.