The catalytic converter could have melted already and plugged up. If you had a fault for an oxygen sensor, the system may have been running rich, or if you had a previous misfire that could cause it to melt or break apart causing a restriction.
To test for a plugged exhaust a simple vacuum test can be done. Find a vacuum source like the booster hose. Normal vacuum at idle is around 21" at sea level more or less. Race the engine at 2500 rpm and if vacuum starts to drop really low then the catalytic converter is most likely plugged up.
Saturday, November 18th, 2017 AT 10:07 PM