Tech Article: Fix Exhaust Fumes in Your Z Before They "Affixiate" You
by Ben Pila,
Member at Large
On 1970-78 Zs, having some exhaust fumes inside the cabin is quite common. These years of Zs all had the same body design and that original design is dated back at least to the late 60s. The way the fumes can get into the cabin is from one of the rear seals or a combination of some of them. If a seal is bad and you roll down a window, often times, more fumes come in. This is due to the low pressure area that is created from the air rushing over the top of the hatch and the air coming from under the body. The air directly behind the tail lamps is not moving and if a window is opened, then the air rushing by the open window actually allows the air that is sitting behind the tail lamp area to enter by the bad seal and get into the cabin (which would be a low pressure area.) So if you do have fumes getting into the cabin, then it is better to roll all windows up and turn on the blower fan until you get the seal(s) replaced.
The most common seal that allows fumes into the car is the rear hatch seal. That seal is the one that goes around the opening of the rear hatch. The rear hatch seal is a rather expensive seal but will last a long time if a new one is installed. Try to avoid buying the aftermarket rear hatch seal as they often don't fit well.
Another area that can let fumes in is the seal between the tail lamps and the body. This area is often overlooked because you can't directly see the seals without removing the rear trim or tail lamps themselves.
At the underside of the rear hatch are two rubber plugs about 2" in diameter. These plugs should not have any hole in them. The rear interior panel that attaches to the underside of the rear hatch should also be fastened securely and if necessary should be sealed with a foam weatherstrip or clear silicone sealant.
A few other things to check is for any major rust holes in the back side of the quarter panels which could let fumes in and the muffler/exhaust system itself should be in good shape too.
If the fumes you smell are a raw fuel smell, then there could be a cracked fuel filler tube, vapor recovery hose, fitting or in some cases (on 240s,) a cracked vapor recovery tank. The vapor recovery tank is located behind the passenger side rear most interior panel behind the rear strut tower. Removal of both the panel behind the right rear strut tower and the rear interior panel may be necessary to do a careful inspection of the vapor hoses and associated parts.
So, hopefully this article will send you looking carefully for the culprit of your fumes and keep you from fuming at the mouth about the fumes.