I have a 2007 HHR LT 2.4 Ecotec 120,000 miles and having a strong exhaust smell emitting in the cabin when I turn on the Heater or Air Conditioner. I did replace the exhaust manifold (detected a crack/leak) and gasket and the smell is still present. I did check the flex pipe (mesh type) but didn't notice any holes. Any idea as to what else it could be? I greatly appreciate any advice or suggestions on this matter.

Thanks.

 

Check further along the exhaust pipe the resonator and the muffler. Particularly the gasket at the flange between the cat and resonator

 

Welcome
May not be an exhaust smell. A dirty, musty cabin air filter can give you some bad smells that could be confused with an exhaust smell.
(since you say it's when the heater or AC is on)
Check the cabin filter.

 

maybe this information will be useful ...

In the first few generations of the Subaru Forester, the smell of exhaust in the cabin was the norm. The reason is a bad rear gate lock. After a couple of years of operation, the hinge of the lock somehow deteriorated and the gate ceased to fit snugly against the rubber seal. When driving, the air flow sucked exhaust gases from the muffler into the cab through the slot. The problem was solved - a thick layer of tape was wound on a loop, but this helped only temporarily.
The manufacturer did not burden himself with the elimination of this trouble, he limited himself only to the statement that "this is the legendary smell of opposite engine." Subaru generally loves to create bombastic myths from scratch.

Why did I write this ... Check the gate seal, check the operation of the gate lock, check the glass of the gate. Make sure the back of the car has no slits. The aerodynamics of HHR are not perfect and the air turbulence is very noticeable at the rear.
I am not claiming that the cause of the stench has been found. But a thorough inspection won't be superfluous. It will not require money and will not take a long time.

 

Welcome.

 

Hello everyone,

Thank you so much for the welcome and all suggestions. I apologize for the late response as I was out of town for the week and was able to finally inspect everything today. Cabin filter was replaced 2 months ago. I checked all gaskets and they were fine. I decided to run a test to find leak in the exhaust system. I attached a vacuum cleaner (blowing portion) hose to the exhaust pipe with the engine cold and turned it on to pressurize the system. I then sprayed soapy water on the system and it started bubbling at the flex pipe on the seal between the mesh and tubing that connects to the exhaust manifold. I ordered the replacement part and will attempt to repair it next weekend. I'll update once the job is completed. Strange how it didn't even sound like an exhaust leak. Again, thank you everyone!

Art

 

It’s a mystery and most members don’t believe it could be the flex pipe, but many times it is, let us know after you get it replaced.

 

If the flex pipe is mesh it is a replacement and the weld broke. The factory flex joint is a solid metal accordion, they crack in the folds.
I suggest that you inspect the motor and trans mounts. That is why flex pipes fail.

 

Yes, particularly the upper engine mount, look thru the oblong hole inside the passenger side front wheel well, is that bolt head in the centre of the hole, or has it sagged down? If so, the mount is toast.