Signal disabling engine diagnosing apparatus

In a system for diagnosing an engine including a source of periodic cycles of ignition signals, improved apparatus for preventing one or more predetermined ignition signals in each cycle from energizing engine components which are normally energized by said predetermined ignition signals comprising in combination:

• input means for receiving said periodic cycles of ignition signals from said source;
• generating means for generating a clock pulse in response to the receipt of each ignition signal by the input means;
• bistable means for generating first, second and third binary output signals each having an initial state and for changing the state of at least one of the said binary output signals in a predetermined sequence in response to each clock pulse so that said first, second and third binary output signals can represent eight different binary numbers, said bistable means comprising first flipflop means including a first clock input for receiving the clock pulses and including a first output for producing the first binary output signal, second flipflop means including a second clock input for receiving the first binary output signal and including a second output for producing the second binary output signal, and third flipflop means including a third clock input for receiving the second binary output signal and including a third output for producing the third binary output signal;
• setting means for initially setting the binary output signals to said initial states by use of a setting pulse generated in response to the operation of a predetermined one of said engine components;
• gating means responsive to predetermined states of the first, second and third binary output signals and the clock pulses for returning said binary output signals to their initial states prior to the receipt of said setting pulse, said gating means comprising first gate means for normally transmitting the first binary output signal to the second clock input and for blocking the transmission of the first binary output signal to the second clock input in response to a mode signal, second gate means for normally transmitting the second binary output signal to the third clock input and for transmitting the first binary output signal to the third clock input in response to the mode signal, means for producing the mode signal in response to an enable signal and the third binary output signal and for terminating the mode signal in response to the termination of the third binary output signal or the termination of the enable signal, and means for normally inhibiting the enable signal and for producing the enable signal when the source generates six ignition signals per cycle;
• adjustable selecting means for producing a disabling pulse in response to predetermined states of the first, second and third output signals;
• and
• disabling means responsive to the disabling pulse for preventing any simultaneously occurring ignition signal from energizing an engine component, whereby the first, second and third output signals are in the same state each time a predetermined one of the engine components is prevented from being energized.