Originally Posted by
MrSwaggerWagon
What color are your plugs? I bet your engine is running SUPER rich, due to what I will explain in a second. (White tips = lean, golden tips = good, black tips = rich)
Oxygen sensors read the composition of the exhaust gasses and, through some calculations, the ECU can determine the current A/F ratio and adjust the fuel going in to compensate for temperature, humidity, and altitude changes. However, when you have damaged or removed a catalytic converter, it screws with the readings of the sensors, which can make the ECU keep adding fuel... This is my understanding of this (and I may be wrong), but over on the S10 forums, there were people talking about how their gas mileage went to shit after removing their cats. Removing cats only really causes problems in post-'94 vehicles, since that is when many vehicles put their O2 sensors after the cats.
Well, you are smelling the excess fuel that has been injected, but there isn't enough oxygen to burn it all... Really, I would replace the stock cats that you removed. This should, in theory, restore your mileage. With the engine running this rich, Even if it doesn't get your mileage back, you will at least be doing the planet a large favor.
Just to make sure, try to find a shop with equipment to analyze your exhaust gas. You can't trust the reading out of the OBD port, since that is the messed up reading that is throwing the ECU into a fit.