If the diaparagm is ruptured, you will get quite a thrill.:lol2:The suck test simply opens the egr valve diaphragm to allow exhaust flow to the manifold. Should hear a little popping noise when the diaphragm opens. Dont worry, youre just applying vacuum, you wont get a mouthful of hot exhaust gas, lol. If everything is working properly (egr valve and passageway is sufficiently open), engine should immediately stumble or die.