Permeability of a good flex pipe

I just got a replacement flex pipe (a cat thief cut the most expensive pipe in the vehicle) and before installing, on a whim I capped one end with my hand and applied a few psi of lung air to the other and found that surprisingly it leaked. I’ve never tested this before - I assume it’s supposed to not leak at all and I got a bad part, right?

If it is leaking out the side of the pipe, then it is defective. what good is a pipe if you are going to have an exhaust leak.

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If it leaks, you could get a the dreaded P0420 code.


I think they all do that before they’re hot. Seriously, look how it’s made. That’s the reason you tested it.

Well to be honest I’ve had bad luck with flex pipes in the past, so I thought I’d test it before it went on the car this time. This unit doesn’t have that universal mesh thingy visible from the outside - there’s a collar and if you peer into the void it appears there’s a stainless spring going around everything - you really can’t see what’s going on in there. It’s not a cheap piece of pipe unfortunately and I really don’t want to do this twice.

Well that’s not the type of flex pipe I thought it would be. Now I wonder if they still make the braided ones. Even so; it may still leak before installation. I hope that’s the case.

Or worse-- The dreaded DOA toe tag.