converter efficiency hence only transport time delay t d and catalytic converter time constant t c will be determined a block diagram of the control system is shown in fig3 where numeral 31 refers to the converter numeral 33 refers to the controller and numeral 32 refers to the comparator corresponding transfer functions are also shown on the fig3 the operation of ecc 7 in controlling air fuel ratio in a manner to estimate the efficiency of a converter is now described with particular reference to the flowchart shown on fig4 and 4a and an associated experimentally developed twc converter efficiency function shown in fig5 at the start of the process in step 4010 engine parameters are read they include but are not limited to parameters which define test conditions and ego switching in this description parameters are read using a constant sampling rate for example 10 msec however in an interrupt driven computer system different counters which will be described later may be substituted by timers this may also require additional steps in the flowchart in step 4020 test conditions are verified it may be desirable to initiate a catalytic converter efficiency test at a constant vehicle speed for example between 20 and 50 mph moderate load and after engine operations are stabilized only one converter efficiency test may be desired for a given driving cycle if the test conditions are satisfied the test may be started otherwise at step 4030 the test subroutine is exited it should be noted that step 4030 will also terminate and reset the test if entry.