Hi all-so I am the owner of a '72 240z, which is a blast to drive, but ever since purchasing the car, it has been plagued by a particular issue that makes it supremely unpleasant: the smell of either unburned fuel, or exhaust, in the cabin. I am not at all new to old cars and their smell, and I can assure you this is not the typical "old car stink" from a non-cat exhaust system. this is BAD. if the windows are rolled up, i can only drive maybe 3-5 minutes before it's basically unbearable(headache levels of discomfort). 

I've had two exhaust shops check everything downstream of the exhaust header-it's completely tight. the car will stall out if you block off the exhaust at the tailpipe. I have sealed off every interior vent with painters tape, and tested-no change. i have gone thru the firewall with a flashlight in the dark, and cannot find any noticeable gaps. I'm basically stumped. I don't want to get rid of the car, but in it's current state, it can only be driven with both windows down, and even then, i have to start sticking my head out the window after 10 minutes for air. this particular car has a fuel pump toggle switch at the center console FYI. my only thought at this point is that there's either A) a firewall leak i can't find, or b) something related to the fuel pump. has anyone experienced anything similar, or have any ideas? thanks, RJ

Exhaust fumes come in through the rear hatch and taillights it’s very common make sure you have those sealed up good and gaskets on the tail lights also make sure holes in spare tire area are plugged


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A couple of things you might check.

1. The inner weather stripping that  goes completely around the rear lid opening and seals the rear window lid to the car body.  There should be an outer seal that only goes 3/4 of the way around (I believe this one is for shedding water) but if the inner rubber seal (that goes completely around) is old, broken, or cracked, you could definitely have exhaust gases creeping back into the car's cabin.

2. The gas tank has an expansion tank that is located in the cabin on the passenger side just above the fuel filler area.  This tank has several hose connections that connect it to the gas tank below the rear deck.  If any of these hoses or the expansion tank have any cracks, leaks, etc. it could lead to you smelling fuel in the cabin.

That vinyl covered cardboard finishing panel on the inside of the hatch needs to be sealed all around its perimeter.  There's a gap around the latch mechanism that lets fumes get sucked in.  The area at the back of the car is a high pressure zone compared to the inside of the car.  Ironically, the problem gets worse when you open the windows because the air flowing by the windows pull air out, which gets replaced from the back end.

One other thing to check after you have done all of the things mentioned above...tail light seals in particular.

On the inside of the hatch, there is a vinyl wrapped trim piece that extends across the bottom back of the hatch. That trim piece needs to be flat and sealed with sealant to the hatch. Otherwise, fumes get sucked into the lock mechanism and in through breaks in the seal of this trim piece. Most of the time, in my experience, after 45 years of not being removed and re-sealed this trim piece is wavy and has many spots where there are air gaps. Last summer, a 72 that I had just rebuilt was filling the cabin with fumes. I had sealed every possible entry point and then it hit me that I had not re-sealed the hatch trim panel. Did that and no more exhaust fumes.

Two completely independent posts on the exact same fix.  Has to be good!

You could always Bosozoku it.

In addition to all of the above techniques to mitigating exhaust fumes in the cabin, you can also extend the tail piece of the muffler another 2-3" to get the gases out into faster moving air and installing a spoiler on the rear hatch disrupts the vortex at the back of the car and can help.

Going Bosozoku would certainly help but would remove 10% of your power and probably get you a big ticket.?

After you have exhausted (?) all other possibilities, remove the left rear quarter interior plastic panel and the interior rear bezel that covers the rear tail lights. Park it in a garage and with the lights off, and from underneath the car and behind the rear wheel, shine a mag light flashlight up and look for light inside the cabin.  There is a flat piece of sheet metal there which extends from the wheel well, around the antenna and to the rear valance. I found a small gap there.  There are also numerous rubber plugs around hoses in the back that can deteriorate after 50 years.

What everyone has said so far, rubber floor plugs, door, tail light, and hatch weatherstripping, take it all to heart.

One other possibility is the hole for the antenna drain hose.  Crawl under the car to make sure you have a good

grommet for that drain hose hole.  While you are under there, see if you see daylight between the edge of the 

rear floor next to the quarter panel.

So where do you find grommets for a reasonable price? Alternative solutions?



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So where do you find grommets for a reasonable price? Alternative solutions?   Sent from my iPhone using Tapatalk     

  

eBay! 

 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F252953962291 

 

Although MSA have the rear hatch ones at a decent price if originality for items on show is of concern. https://ebay.us/o3iou5 

 

Firstly, I had the same issue with my car and I did much of the above, it's all great advice up there. I started out using masking tape to seal up all the areas that could be responsible; then went for a drive and little by little removed the tape until the the smell came back. Then I would plug that issue and repeat until it got sorted.

 

You do look a little silly driving with tape all over your rear end - a bit like loo paper hanging out of the back of your trousers / or shoes!

 

 

Areas mine was leaking:

 

Rear hatch vinal panel: sealed with D shaped black draft excluder used in your home.

 

 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F372485235841

 

Missing rubber bungs at the bottom of the hatch. This one and the one above made a HUGE difference.

 

Finally, the car was very bearable but still felt light headed after and hour so.

 

The inner rear hatch weather strip looked fine but was loose in places. Re-glued it on all round.

 

Lifted up the rear deck area carpet and found one missing bung in spare wheel area.

 

Then took off the rear inside trim behind the tail lights and found lots of daylight through the hole where the fuel tank breather pipe goes. Again a bit of creativity with insulation.

 

My tail light gaskets were just fine.

 

I can now drive ALL day and the only thing that hurts are my ears from driving with the window down and grabbing the next gear at over 6k rpm all the time. Oh and my facial muscles hurt from constantly sporting an inane grin like a four year old when I do this.

 

The PO of my car did a great job of body work resto but wasn't into rubber and those VITAL little things - but then again he was a polish and display man who did 800 miles in 5 years between shows, so it probably didn't even register.

 

Good luck and keep us posted on your progress. There is always something new to be learned from other people's experiences!