Smelling exhaust fumes inside car and can't find source

[Jim S]

I have gone through and sealed every hole in the firewall where wires, hoses etc. pass through.  I had a muffler shop weld the entire exhaust system and have new manifold gaskets.  They could find no leaks.  But when I drive, I still smell fumes. I'm baffled.  I read somewhere about fumes that can get pulled in somehow from the end of the tail pipes?  Does anyone know more about this and how it could get inside the passenger compartment? And most importantly, how to stop it!

[Footer]

It seems like I can get a whiff of exhaust in my car but only when going down the road with the windows down. I’m wondering if the same great aerodynamics that don’t allow any buffeting with the windows down also allow the exhaust to work its way into the cab. Anyone else noticed this?  Mike

[64StudebakerAvanti]

There is a hole under the gas tank that seems to have no purpose. The partition between the tank and rear seat is sealed with dumdum. Perhaps the dumdum is cracked, brittle or otherwise compromised allowing fumes to enter.

 

[Mel]

I sealed this 'mystery hole' with a piece of 'sponge plastic' -- I don't know else to call it -- It's that stuff heavy appliances are packed with.  I cut a circle slightly larger the hole diameter and plugged it up.

Don't know if your set up is like this, but my ('67) motor had a hole about midway back on the bottom of the right exhaust header, as I recall, close to the block; this may have been for a 'heat transfer tube' leading to the carb for the choke.  My setup did not require this.  I tapped the hole and put a bolt in it to stop it up.