I’ve been having an issue with getting exhaust smell inside my 71 skylark. I have a stock ‘70 455 from an electra, with a set of MT repro headers that I bought used at the first BPG nats. The exhaust is 3” X pipe system produced for the GSCA about 15 years ago. I am fairly certain that the leak is not coming from where the headers meet the head, I cannot hear any tell-tale ticking under load. I felt around the collector gaskets and cannot feel or hear any leaks there either. The stranger thing is that when I am moving, I only get the exhaust smell if I am driving with the windows down. If I keep them up, I don’t smell it at all. I have tried driving around with a CO detector in the car. It does register low levels of CO sitting still on cold start, before the choke turns off, but once it is warmed up, I don’t register any CO on the meter whether the windows are up or down, moving or stopped. I love driving my car, but I’ve hardly driven it the past few years because I can’t stand the exhaust smell. Does it sound like I’m overlooking anything obvious? Thanks!
I don't know the condition of your car, but are there a lot of big rust holes in it? The only reason I ask is because back in the day of the station wagons...the rear window would roll down...you could get the same effect. I used to have a 67 plymouth fury III wagon with a power rear window. One day I was driving down the road with the back window open and was getting a lot of exhaust inside of the car. I stopped doing that immediately. I also heard back in the day that some kids sitting in those rear facing seats asphyxiated on the fumes...sad stuff. I also had a shitty 78 chrysler cordoba (back in the day) and the rear quarter had a softball sized hole behind the wheel. the exhaust exited right by the hole in the body. That caused a lot of exhaust fumes to get in the car as well. Kind of makes sense with the windows being open and the air swirling around...instead of it slipping up and over the car.
Take it to a muffler shop they have a detector. I had a leak in my exhaust manifold once that drove me to the muffler shop. A couple hours later and about 200$ later it was good to go.
CO is colorless and odorless. Test again with a meter that detects hydrocarbons (HC). Do you have a hood seal at the cowl? REALLY common for under-hood fumes to come out the back of the hood, and get pulled down into the grille ahead of the windshield--directly into the HVAC system for the passenger compartment. Holes in the firewall, including OEM holes with deteriorated seals? Holes in the floor, including the trunk? Deteriorated seals? And I'd be looking for evidence of misfire and/or oil/fuel leaks.
Yep, Dave is correct. Any leaks in the body- rust holes, etc, will cause the exhaust to suck into the passenger compartment when the windows are down. You can try replacing the package shelf and adding some jute insulation under it. Also remove the back seat and inspect the cardboard trunk divider. You can also add a some jute insulation to the cardboard to insulate the trunk from the passenger compartment. You might want to also check the trunk weatherstripping. The fumes may be coming through the weatherstripping
Hmm well my trunk seal is shot. My package tray is also shot, and it has 6x9 speakers that have long since decayed from sun exposure. I know the car has some bondo in the lower rear quarters, behind the rear wheels that was done by a prior owner. I will inspect that closely to see if it has been compromised. That also reminds me, that about 7-8 years ago, I had the driver’s rear tire come apart at highway speeds, and tore up the inner wheelhouse, I guess I should get under and make sure there isnt an air leak there either. Luckily the floorboards are rock solid on the car, so I don’t think there is an issue there. I do have the cowl seal on the hood, and it seems to still be in good shape. I’ll also double check the firewall, I did drill a small hole there a while back when I swapped to Global West front suspension and disc brakes, so that I could have a manual proportioning valve imside the car. I will have to check around for a local shop with an exhaust detector, I didn’t know that was a thing. Thanks everyone for the input!
