[Champ6]

I was getting a LOT of pre-cat exhaust in the cabin, the muffler shop said they found a crack at the cat inlet and welded it, but no improvement. So I took it to my VW trained local mechanic. He dropped the exhaust, found the crack extended to the back side and welded that. Still, I get exhaust in the cabin, and at rest, I smell it under the hood. There has been NO detectable noise suggesting a leak or crack. Now I have a P0420 code which could be related.
Can the SAI system cause this? If not, what else might be causing this?

 

[WtErKeWlEdUbbEr]

Sounds like you still have an exhaust leak. That code pops up for leaks too.


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[Champ6]

Sounds like you still have an exhaust leak. That code pops up for leaks too.


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Thats obvious. BUt an exhaust shop and a VW trained mechanic can't find it, and it is silent. So where do I look if they can't find it?

 

[WtErKeWlEdUbbEr]

Thats obvious. BUt an exhaust shop and a VW trained mechanic can't find it, and it is silent. So where do I look if they can't find it?

They should be using smoke from a gas welder to find the leak. I’ve seen muffler shops find leaks like that.


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[cylinder head o7k]

i bet the welds didnt fix the problem

 

[Champ6]

Back to the exhaust shop again this morning because the issue still exists. He still can't find a leak. P0420 cleared itself after 100 miles or so. No other codes

Could the secondary air system have a failure and leak exhaust? Or does anyone have any other ideas?

 

[cylinder head o7k]

it can fail but not really leak exhaust. exhaust would have to travel back up the sai system then leak in the engine bay.

 

[Champ6]

Thanks, I checked yesterday and no evidence of it malfunctioning. Based on teh movement I saw just revving the engine, my current theory is a bad engine mount and when it rocks, the flex pipe leak becomes apparent, but when it is just idling, it doesn't so that's why no one has found it. Otherwise, I am totally out of ideas.

 

[cylinder head o7k]

the flex pipe is a weak spot in the exhaust. had mine break and basically accordian out in length and never got a code for exhaust malfunction.

 

[Champ6]

Has one ever cracked and never made noise or blown a torch out?

 

[cylinder head o7k]

mine didnt make noise i found it while inspecting other parts

 

[Champ6]

OK, I see no other other possibilities, so I'll replace the mounts and teh flex pipe. Thanks!

 

[cylinder head o7k]

theres always other possibilties its a vw

 

[Champ6]

After all others and I have checked, what's left?

 

[cylinder head o7k]

could be exhaust getting in the car just from the tail pipe with no leak. could be an area on the underside of the vehicle that allows exhaust in.

 

[Champ6]

Here is the final result: I replaced the flex pipe. Splitting the old one open, I could see one joint that would open and close when it was flexed. That and new engine mounts, and 2 weeks later, I've not smelled exhaust in the cabin. Thanks everyone!