WJ cat/ o2 sensor problem

[Chancer]

Hi, I'm looking into getting a 1999 4.7 V8 WJ, and it's running very rough (ie, cheap!). Apparently the lambda sensor is melted and as a result is running very rich. Would it just be a matter of picking up a new sensor, or is it likely that the cat is also damaged? Any other causes I should be looking at?

TIA

 

[89Daytona]

It should have 2 oxygen sensors (one on each end of the cat). In the US some auto parts stores (Autozone and Advance Auto) offer free diagnostic checks with a scan tool. You should check the codes to see which one is bad and see if anything else is wrong.

 

[Chancer]

The jeep's currently 200 miles away from me, but I managed to get the dealer to check the engine codes - nothing. Is that a good sign, or is it suffering from short term memory loss?

Symptoms:
The "lamba sensor" - I guess the upstream o2 sensor - looks as if it's been melted and the engine runs very rough, evening out if you can get it to over 1500 rpm. Does that sound like a blocked cat?

The guy that came to look at it yesterday thought that it had an earthing fault on the ECU, but I can't really see that. Thoughts?