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I don't think he has the option of modifying the emissions system in order to pass the required test, so everything he does needs to be quickly reversible (posted earlier by Sentra).
While injecting extra fuel may help light the cat faster, I don't think he can do that and make it easily reversible, so he risks automatic fail of emissions testing, plus the cost of the modification, with potentially no benefit.
Eliminating any engine off coasting may be the only option, but it may be possible to combine heat conservation and accomplish the same thing with EOC. I don't know if that is possible, but DFCO allows oxygen to flow through the cat without fuel, so it would seem like that would cool the cat off more quickly than shutting the engine off, with no O2 passing through the cat.
How long can you allow EOC versus engine running before you pass the threshold of temps required for proper cat performance?
How long does it take the cat to cool off beyond it's design parameters?
The best method of answering those questions might be to monitor the second O2 sensor which is there to monitor cat function. This would give him a voltage input that should show whether the cat is working properly or not.
It's funny that he had not post cat O2 sensor codes, but that may be the ECU "thinks" every restart is a cold start and expects no proper reading without a certain run time period.
regards
Mech
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