This is one of the most common, and perhaps the most deadliest problem that concerns the first generation z car. Exhaust of course contains Carbon Monoxide or CO, which is known as the silent killer. I’ve solved many health related problems over the years in my customers cars that the doctors had trouble diagnosing. The problem was CO inhalation and it can cause some very serious side effects. I cannot stress the seriousness of this problem enough. IT NEEDS TO BE FIXED YESTERDAY NOT TOMORROW! The problem is worse if your lower shift boot is torn or if you put a window down. The exhaust is actually coming in through the rear end of the car. If you look at the underside of the rear hatch you can probably see a line around it from the rear hatch seal. That is like a fingerprint. The outside of that line is usually darker especially on the drivers side (the side that the exhaust pipe is on for you fairlady owners) and that is from the exhaust. Carefully look at that line on the rear hatch and make sure that it looks even all the way around the hatch. Look for any area that the black crosses over to the other side of the line, i.e. the inside of the gasket surface. Especially if your gasket has a seam in it. If there is a gap on your seal then either repair the gap or replace the seal. The hatch gasket must be firmly glued to the body all the way around or it could leak exhaust into the car. Next look at the inside panel on the rear hatch. If it isn’t fastened securely or it has the gravity droops, then exhaust can and will come in through that panel. The panel must be flat and sealed against the hatch tightly or exhaust will come in through that area. We now sell that panel new in all stock colors.
On the underside of the rear hatch there are 2 holes about 1.5 inches wide. They are supposed to have rubber grommets in them, unless you’re a fan of the Red/Green show and in that case use duct tape. If you see an area of the hatch that you think isn’t sealing tightly against the seal, you can take dollar bills and lay them across the seal half in and half out. Then shut the hatch tightly and see if you can pull the bills out with little or not resistance. In this case resistance is good, that means you have a tight seal. If the hatch doesn’t lock down tightly against the gasket, then you may need to adjust the striker which is accessible by pulling the license plate light assembly. Once that is out of the way you should be able to see the striker. Loosen the 2 bolts and lower the striker down a little bit, then tighten the bolts.Temporarily you can stack pillows across the back of the car inside, so that the hatch will compress them when it’s closed, and that can slow down or even completely stop exhaust from coming into the cockpit. We usually carry the rear hatch gaskets in stock if you need one.
There is also an antenna drain hole right by the muffler. It should have a rubber grommet in that hole with the drain tube coming through it. If the drain tube has come off of the antenna, or if the grommet is deteriorated or missing then that area has to be sealed accordingly. Look at the underside of the car very closely and see if it has ever been rear ended and improperly fixed. I have seen the floor buckled around the spare tire compartment and a couple of gaps in the seams is all it takes for exhaust to find an entrance into the cockpit. The tail light gaskets must be sealed tightly also. There are some grommets in the rear floor pan area that fuel vent hoses pass through. Make sure that all of those grommets are sealed properly. ANY HOLE OR GAP OF ANY SIZE IN THE BACK END OF A FIRST GEN Z CAR CAN AND WILL ALLOW EXHAUST TO COME IN.
When installing an exhaust system on a first gen z car it is very important that you set up the outlet of the muffler in the proper spot and with the appropriate end. There is a vortex behind every z that swirls around. Picture a big tube behind your z that runs from left to right and spins. This is what the vortex would look like in a wind tunnel. If you have a rear spoiler and/or ground effects on your z, then that vortex is even larger, depending on the type of rear spoiler that you have.
The idea is to direct exhaust away from that vortex as much as possible. It not only takes the pressure off of the rear hatch seal etc. but it saves the back end of your z. Look at the majority of z’s on the road and the left taillight is darker than the right, the left side of the bumper is tarnished more than the right and so on. This is because of the exhaust being forced into the vortex. On a stock exhaust almost all of the exhaust goes into the vortex so you need to put a turndown tip on the end of the exhaust to channel it away from that vortex. The end of the tip MUST BE before the end of the rear bumper or it will not work properly. This means that you should never use a Super trap type muffler also. That is perhaps worse than the original stock straight tip. The turn down tips are available at any exhaust shop, and we also carry them in stock. They must be welded or clamped solidly to the pipe. The ones that are held on by a couple of screws will still leak, and eventually fall off. We do have pictures on file to show the type of tip, and it’s position in relation to the rear bumper, so if you need to see a pic we can e-mail it to you. Just let us know. We also build custom exhaust systems on site for your Z, and usually have turbo mufflers etc. in stock.
If you have any breech in the back of the z that lets exhaust in, it will allow more exhaust to come in the passenger compartment when you lower your window. If you have a manual transmission car you must also make sure that your lower shift boot is not torn. That does the same thing as putting your window down while driving.
If your car does have this scenario, you should always leave the heater fan on high. This will lower or in some cases temporarily stop the exhaust from coming in through the back of the car. If your engine is not burning clean, then the amount of contamination coming inside the car will also be a lot worse because the air will have even more CO in it.