Had a problem with the exhaust rusting out,so I installed a 2.5in to 2.25 dual out. The sleeve where the exhaust slides on was loose so I removed it and installed the muffler there instead with turndowns. I would estimate that it is around 16" maybe less from the cat.Would it be too close?Only a week after this install my truck started to stall and the check engine light appeared.While ideling in park and with one or two revs,it will kill the engine. Truck has almost 250k miles on it..and pulled up that code 36,so maybe clogged cat overheated the sensor? Let me know what you guys think.

 

I have a glasspack close behind my cat with a side exit, and I have no problems...shouldn't be too close. Actually, I have been told by guys that do exhaust work that putting the muffler as close as possible to the cat is better because the heat keeps it from rusting. With your mileage, I would check to see if the cat is clogged.