94 Accord EX, F22B1 engine (Philippine Domestic Market). Stock exhaust system with muffler.

Whenever AC is on and I'm on the highway, or when I'm going fast and on a high rev, I smell exhaust smoke coming from the A/C.

Tried revving it while parked and smelled the engine bay. Same thing, I smell exhaust smoke, even if exhaust is far away and wind direction is away from the engine bay.

What could be the cause?

This just started a few days ago, when I started using 100 Octane fuel and some additives to clean my engine out. I dunno if that's what caused it.

Any help guys?

 

If you are smelling exhaust smoke, I would look for exhaust leaks. Take off the exhaust manifold heat shield and look for cracks.