I have a 99 Blazer with 115,000 miles on it that has a sputtering problem when the truck sits overnight. It had sputtered every once in a while in the past but always went away after a few seconds. Now it will sputter for a few miles and go away. It also has a hesitation problem and the fuel mileage is bad. Would the catalytic converter be the culprit? I had to replace the fuel pump about a month ago because the truck would not start. I was hoping that would solve the hesitation problem but it didn’t. Also, no code is popping up leading me to believe it is a clogged catalytic converter. Is there something else I need to look at?

 

Clogged converter would at least set a code in the pending area for the OBDII, if you feel that is the problem get the codes scanned to see if there are any pending. It might indicate an O2 sensor problem. The truck should have an O2 sensor before and after the cat to tell if it is failing...

 

im pretty sure my cat is toast, it always rattles, and it hasent set any codes..........

 

There are no pending codes stored. The only codes that showed in the history was a random misfire code that happened before I did a tune up. The truck runs fine after it has been ran but when it sits overnight it wants to sputter and carry on like a transmission would do if it was going out. I plan on taking the catalytic converter off this weekend so I can see what the honeycomb looks like.