My 2004 TB LT was running great until about 4 months ago. There is a major hesitation when accelerating (especially going up hill and also when passing and/or merging) and shifts very hard from 2nd gear on. We took it to the dealer, they ran a diagnostic on it and said the catalytic converter is out. They want to replace it for $1000.00 plus labor. On top of this, we ran it through emissions and it passed 3 days before we took it in to the dealer. Can the catalytic converter really be the cause of this? Thank you to anyone who can help me.

 

To me it doesn't seem likely the cat would go out "unless " you have been running around awhile with a faulty thermostat that is causing it to run too cold . This could plug up the cat if this was happening. The guage should run right in the middle almost straight up if it is working ok . If so and it was plugged then yes it could cause major hesitation . Do you have any CEL on ? Just by your description it could be plugged but I wouldn't change it until they can tell you why it plugged which it should never do if the car is running right . The culprit with the Envoys is a stat that doesn't close and this causes it to runn too rich which will plug the cat. I would have them check that to see if the vehicle is ever getting up to the correct temp . "Usually that should light a CEL if it is running too cool .

 

a cat will plug up from driving a vehicle with a miss firing engine.my sons friend had the same year trailblazer that you have and his vehicle was doing exactly what yours is doing.it had no power and would take a long time to shift.he brought it to me and i could hear the engine missing.he had a number four cylinder miss fire.i told him to change out the plugs and replace the cat because when you accellerated the engine there was hardly any exhaust flow coming out of the exhaust.he replaced the plugs and cat and his problems went away.you could have another issue or issues altogether thats causing your problem,like a plugged fuel filter or and bad mass air flow meter.hope this helps.