Medium duties are weird beasts indeed. Well, FWIW the air pumps still can -help- with unburnt fuel... It's not as good as a Cat for emissions but it's better

Medium duties are weird beasts indeed. Well, FWIW the air pumps still can -help- with unburnt fuel... It's not as good as a Cat for emissions but it's better than nothing, so they actually started being used before Cats; they just are used different now.