Smoke Smell in Cabin/Engine Bay
 

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.