Fumes…yuck…air pump maybe? 72 fury wagon

I get what seems like exhaust fumes. Back window is closed. Other Windows open or closed doesn't matter. I read the thread on wagon exhaust and mine appears to be correct making a 45 degree to the side and turned down.
I inspected the exhaust pipes and muffler and manifold flanges and nothing visible or heard.. no ticking of exhaust leak... so I'm wondering if a fault in the air pump system could be the cause. The engine is a 400. ....
Author: MBar