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.  

[AG-R3]

Might be your trunk lid weatherstrip.   

[Mark L]

What about the channels where the nut plates for the seat mount bolts are located? I've seen in other posts that if these channels is not sealed, they act like ducts to move air and any exhaust under the car into the cabin through the floor.

The exhaust under the car would be from the tail pipes. The axle, other things under the car, and the shape of the well above the rear axle may create a draft that pull the exhaust forward under the floor.

Edited Thursday at 02:47 AM by Mark L

[Jim S]

Thank you all for the tips.  I will follow up on them.  I also am getting a lot of heat inside from the engine.  I covered the floor and firewall with a heat barrier under the carpet and sealed all holes, yet it gets very hot inside when I drive.  Is this normal for an Avanti?  My 64 Hawk never had this problem.

[ronmanfredi]

The engine compartment is a heat trap and a lot of that heat escapes down the tapered entrance to the transmission tunnel.  I removed the dash and gutted my 63 for customization and while I was there, I installed barrier everywhere including all of the console.