We presented nine new black box delay fault models for non-scan sequential circuits at the functional level, when the primary inputs and primary outputs are available only. We examined the suggested fault models in two stages. During the first stage of the experiment, we selected the best two fault models for further examination on the base of criterion proposed in the paper. During the second stage, we used the functional delay fault model and two black box delay fault models from the first stage for test selection. The comparison of fault coverages was carried out for transition faults. The obtained results demonstrate that transition fault coverages of tests selected based on proposed black box fault models are similar to coverages of tests selected based on functional delay fault model that uses the inner state of circuit.