Exhaust smell after sealing off air vent

[mark248am]

Hey guys, I recently had an AC system installed in my 240z, it's a second generation 280z AC unit and I had an issue with it since I kept feeling hot air coming into the car at high speeds. So after a bit of checking I noticed two leaks from the firewall which i sealed off and one more larger hole on the passenger side, under the dash that brings in air from outside (picture attached).  I ended up sealing that large hole as well with insulation foam and it solved my hot air coming in issue BUT, now I have another issue.

I can now smell exhaust fumes in my car. My theory is when I sealed that large hole the air pressure in the car changed and it is now sucking or letting air in. Does that make sense?

[Mark Maras]

 Yes, it does make sense. Start looking in the rear for fuel line grommets, weather stripping and tail light gaskets that are leaking. These cars are notorious for sucking exhaust into the car.

[SteveJ]

Don't forget about the antenna drain grommet, too.

[siteunseen]

What about adding a tip extension on the muffler?  

[mark248am]

can someone help me understand where the exhaust could be coming in from? For example could it be a hole in my exhaust pipe or is it coming in from the rear of my car? The reason I'm asking is that it's coming in as I'm driving, shouldn't the wind be sending the fumes away and behind my car as I drive instead of inside the cabin? 

[mark248am]

15 minutes ago, siteunseen said:

What about adding a tip extension on the muffler?  

I think I'm gonna try that, make the tip stick out beyond the bumper although looking at a side shot of my car it seems the tips already are passed my bumper. Need to go down to my car and take  closer look

 

 

[Zed Head]

Cars drag a pocket of dirty air behind them.  The air passing over the sides of the car creates a pressure differential inside the car.  The air pocket at the back is higher pressure than inside the car.  So whatever is in that pocket of air will be pushed inside, through any small holes

The hatch framework has holes that can't be sealed easily like where the latch attaches.  The big vinyl covered panel on the inside of the hatch lid is open to the framework.  It can be be sealed to stop the air flow.  Simple adhesive weatherstrip will do the job.

[mark248am]

10 minutes ago, Zed Head said:

Cars drag a pocket of dirty air behind them.  The air passing over the sides of the car creates a pressure differential inside the car.  The air pocket at the back is higher pressure than inside the car.  So whatever is in that pocket of air will be pushed inside, through any small holes

The hatch framework has holes that can't be sealed easily like where the latch attaches.  The big vinyl covered panel on the inside of the hatch lid is open to the framework.  It can be be sealed to stop the air flow.  Simple adhesive weatherstrip will do the job.

Ah that's interesting information, thanks 

[gwri8]

Just curious, did this just start happening when you sealed the air intake chimney under the cowl?  Was there nothing attached to that like a blower or something?  If so, what would happen if you unsealed that vent? Just seeing what sticks.

My 77' came with a very long tailpipe to get past the huge bumper. I have no bumper at the moment and a very short tailpipe. No fumes. But I do have all new gaskets in the rear…..

[mark248am]

Yeah it started happening after i closed the air intake chimney. There was nothing attached but I'm guessing there must have been something attached. But my mechanic removed the old fan/heater and installed an AC system and I'm guessing he left it open. If I unseal the vent things would go back to how they were, air coming in from the outside and no exhaust fume smell. Problem is its like 120+ degrees here right now so having hot air coming in through that vent isn't an option.

 

 

[Patcon]

the cowl vent use to mount to original heating unit and fresh air vent.

Zed is right in his description. The beautiful shape these cars have tend to force air in from the rear of the car. Even if the windows are down. You will need to remove the interior panels at the rear and check all the places that hoses go through the body as well as the seals around the tail lights. also the hatch seals need to be good and it needs to latch properly...Seal them up either with the proper seals or some silicone based sealant

[hr369]

Probably don't have party smoke machines in that part of the world but they're great for chasing down leaks if you set it inside the car and go around the car looking for smoke escaping.