P0420 + hesitation/pinging under load question

I've got a 2000 4.3 with 140,000 on it, and its throwing a P0420 and a P0430, and hesitating. MPG is noticeably down, perhaps to 16 from 18MPG. I assumed plugged catalytics, but I checked the back pressure and it is in the green with resistance well within spec all the way through the RPM range. I'm changing both upstream 02 sensors this week because they are original and I imagine need to be changed anyway.

My question is ... if a catalytic is NOT plugged, can it still cause hesitation and pinging if it is beyond its service life? I would assume it would just throw codes and fail emissions ... the sensors on the other hand, seem more suspect to me, as I could be running super rich.

Any thoughts on the cats or what I should be looking at? THANK YOU!

Check fuel pressure also fo the hesitation, good chance the cat is just bad in respect to emissions issues.

Diagnostic Trouble codes P0420 & P0430 are only thrown when your cat's are blown out.

It's probably time for a good tune up.
1) New Air/fuel filters.
2) New plugs
3) Clean the MAF & IACT sensors with CRC MAF sensor cleaner.
4) Clean throttle body.
5) New upstream H02 sensors.

See http://www.catalyticconverterwarehouse.com , for new OEM cats.

One thing you can try without using a back pressure gauge is to remove the front O2's and see if the pinging and hesitation go away during a quick test drive.

David

I would first check the fuel pressures and make sure that the pressures on engine shut down do not drop rapidly. you may have fuel leaking from injectors/regulator causing an overly rich condition that the PCM cannot control.

then replacing all the O2 sensors obove 100,ooomiles of use is normal preventive maintanance.

as mentioned remove the upstream O2 sensor and go for a test run.

If the issues go away then the exhaust system is restricted.

with the codes this is most times the converter..could be muffler ..how old is the muffler condition etc...

If you find a defective flooding fuel delivery system I would expect a damage converter...on starting a cold engine go under the vehicle and with your hand see if the converter gets hot...If it does not get very hot then it is junk....