Hi Guys, I'm new to the forum, wish I didn't have to be here.


I have a 2001 Ram 1500 5.2 240,000 miles. I've owned it since 160,000 miles.


Never any issue with performance.
Burns a quart of oil every tank of gas.(Probably Plenum gasket, future project)
About a month ago I got a check engine light code P0420.Preformance was not affected.
Replaced upstream sensor(ie closest to the engine), cleared code and drove about 40 miles then the light came back on code P0420.
Replaced downstream sensor(ie farthest from the engine), cleared codes now it will not stay running.
Starts fine, put it in gear and it will run but once I'm moving and let off the gas it dies. It just drops off like I turned off the key.
I can drop it into neutral and it will start right up. Limped home with left foot on brake and right foot on gas to keep it running.


I figure the cat is bad but why was it running fine before the new sensor then won't stay running with the new sensor.

 

Remove the upstream sensor, unscrew it and unplug it. See what happens while driving it. It will throw a code.

 

OK, so I removed the upstream (pre-cat) O2 sensor and took it for a drive.


I drove it till it reached operating temp with no issues. I suppose that means the cat will need to be replaced.


Any recommendations or ones to stay away from.

 

Yup.

There is a high flow cat you may want to try...


But, until your plenum is fixed, you're just going to start plugging up the new cat too...

 

I put the O2 sensor back on and now it runs fine again. The check engine light even went out after about 15miles of driving. Who knows?


I am replacing the Cat right away.


Your right about the Plenum.


I need to get it to pass inspection short term then the plenum repair to come soon after.


Thanks for your input and help.

 

Probably a bad connection on your O2 sensor then.