I am trying to determine if my cats are going out, or my O2 sensors are shot. I suspect some contamination post of of head gasket issue last year.

Current state

No codes at this time
Performance was sluggish - added injector cleaner some improvement, currently running some "Cat Cleaner" as an O2 sensor clean. My O2's are reporting better, performance is much better after about 60 mile of driving.

However my O2 sensors are not consistent in the their activity

• Rears are generally at .6 -.7 of a volt in a flat line but have dropped to zero for short times and tend to float down to .4 -.5 Both of sides are pretty similar
• The fronts are all over the place but settling down a bit,since the Cat Cleaner was added. They do not have a nice sine wave as rule even at idle - it does happen but not consistently and not for long
• The fronts are more random peaks and bounces
• I have not checked cat entry and exit temps as yet
• No exhaust leaks warm, small on cold right side

Suggestions on further T/S steps the Disco runs fine, other than a small heat increase on long uphills (everywhere where I live) at under 1500 rpm about 20 to 25 MPH and the noted performance issues.

My knowledge of cats and O2 is small so looking for some direction, I have no issues replacing the Y pipe and installing new O2's if required.

 

Some images time & O2's engine temp was between 183 and 194, time is minutes and seconds

Front






Rear

Rear

 

Here's a shot of mine over a 10 mile stretch. I'd say your rears indeed look pretty funky.

 

For the hell of it I ran a graph on my 04 over about 10 miles too. The sampling rate is way different, apparently I changed it on the 03 at one point because 10 miles was 6,000 rows where as in the 04 below it was less than 400 rows. Therefore the 04 graph is very peaky and the 03 above shows long plateaus. Note that at the end of the drive and sitting at idle here one of the rears flatlines a bit too.

 

OP: the front O2 sensors are supposed to oscillate back an forth between about .1 and .9..averaging somewhat at stoch value, so what you are seeing is normal. the rears do look a bit wonky... were they up to temp? I think there is a few min delay after starting before O2's are read by the ECU.......

 

@ahab thanks for the graphs, I am going give the cleaner another few days. I have short off road trip this week end, if the rears are still ugly after that I will replace them and continue checking. I have torque setup to log so it is easy to check

@XRAD they were, but as noted I will have a better idea after this weekend

 

I took @XRAD question into consideration perhaps it was more of the hi /low speed issue for teh trip, below are the results for a dump run I did about 45 minutes the flat line would be setting while unloading and not breaking 1000 rpm. Route was uphill, and some down hill largely coasting at towards end