I have a 90 w250 that I'm wanting to redo the exhaust on and from what I've heard if you remove the cats and o2 sensor it will just dump a bunch of fuel into the engine. I was wondering if there was a way around this. A way I can remove the cats and o2 sensor without throwing the computer into a hisssy fit and causing bad fuel economy. Or a way to make the computer forget it ever had an o2 sensor. Any input would be very helpful.

 

you need a O2 sensor no matter what to make the fuel injection work.

 

A 1990 truck will only have pre-cat O2 sensor. (likely just one, possibly two... depending of Federal, or California emissions.) So, the cat doesn't matter. You NEED that O2 sensor though.