Fuel and exhaust have distinctive odors. If the odor is exhaust, I would checkout the exhaust manifold gaskets, especially if there has been any recent head work. It is possible for the exhaust gaskets to be installed backward.
With the engine running, but cold (first start), feel around the exhaust manifolds for leaks, listen for ticking sounds as well.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.