Worse gas mileage after new cat. converter installed
 

2001 S-10 Blazer with @ 134,000 miles
I had catalytic converter and fuel pump replaced and ever since my gas mileage is worse. I always set my trip and used to get 242 miles per tank. Ever since new converter, now I only show 200 miles on trip gauge. Anyone know how or why this is possible? Thanks so much!

How did you know the cat was bad? Normally the catalytic converter doesn't go out unless something is out of spec. For intance engine running too rich and dumpning raw gas into into which could very easliy cause a flash fire (I'm just throwing that out there). Could need a tune up or have some dirty fuel injectors or improper fuel pressure. Might be an O2 sensor, have you cleaned your MAF lately?

First, thx for answering my post. Yep blazer had a tune up a couple of months ago. It was sputtering with no power. Garage said converter-they showed me and it was bad. I don't know where MAF is even located so that's a no for cleaning. It would make sense though cuz 1 of the error codes for my check engine light is coming up MAF. However, why is this just happening since the converter has been installed.

Usually if the cat is fouled up, so are the o2's and get replaced at same time. The MAF is easy to clean so i'd start there. its sitting in the intake system between the filter and throttle body, and held on with couple hose clamps. you can buy cleaners for it in a spray can. if u still have troubles after that check in with the mechanical & maintenance part of the forum.

I'm going to come at this from a different direction. How are you calculating your fuel mileage. Changing the fuel pump also changes the float. Are you putting the same amount of gas in at 200 miles as you were at 242. I would suspect your gauge is just reading a little lower.

I replaced my fuel pump about a year ago and my low fuel light now comes on with over 2 gal. left.