Looking for advice on how to tell if my cats are blocked,

What is the normal running temp reading via OBD2 for cats on 5.0 XKs?

After the car heats up from driving in traffic, acceleration becomes poor and
at idle I don't feel much pressure coming out of the exhaust tips, fuel trim goes -10 at idle.

What's the best was to diagnose?

 

Just a few ideas on the subject:
What would you do if they were blocked?
Have you sourced used cats?
Do universal cats exist?
In the 80s I think GM had beads in the cat, so some folks would empty the beads.
Just opening up the discussion!

 

Remove O2 sensor, look in with borescope/etc

Measure temp drop across cat.

Do clever OBD stuff (is it possible?)

Get weird 1-bank errors due to exhaust gases not flowing properly.

 

I've done the borescope thing and it was definitive - there were chunks laying inside the housing.
Get a Laser Temp Gun and check the exhaust temperatures immediately before the cats and after the cats. The catalyst housing itself will be much hotter during normal operations. If pre-cat temps are way high compared to a ways after the cat, you have problems.
You could also remove the Fuel/Air sensor (the front "Oxygen Sensor" is actually a fuel-air sensor, the aft one is Oxygen) and see if you get a LOT of exhaust exiting. Your vehicle will not run well in this case however.

 

Will check with temperature gun and report back,
Thanks for replies,

If they are bad my first fix is bang on it with a hammer ho allow the flow to push all the crap out
hopefully unblocking it.

 

You will get a CEL for that cat in that case. There are ways around that though, like using a Sensor Extender or whatever they are called. Those are a tight fit on these cars.

 

Don't bang on the cats! Those pieces will just get stuck in your mufflers causing further problems. Remove the cat and replace it or gut it and then re-install.
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I won't have that problem, i'm running x-pipe to quad tips with no muffler.

 

Update, temperature indeed is much higher on precat piping vs post cat piping.

Ran 2 bottles of cat cleaner through the car, not sure if it helped at all,
but I won't bother changing cats until I get an actual code for catalyst.

 

From a "seat of the pants" perspective, a car with clogged cats will be very responsive at low rpm and drop off significantly in performance at higher rpm. When it gets really bad you'll feel like you are in limp mode.

 

And there was a big “bang” sound. It was not a back fire. Engine was fine, though rpms dropped, engine light on, but it recovered. I’m guessing a build up of pressure has to release somewhere.

Anyhow, its like a filter. Reuse any filter for a long time and report on the flow. At 160,000 km, I’m contemplating its time for #3. Kat Klean needs to be applied every mo in the summer to keep away the check engine light when I floor it now. And I never want to experience that BANG again.
I’ll tell you one thing, once its changed it’s invigorating. Car is happier, more efficient, more vigor.
And I walk a different path than many gearheads. I wouldn’t scar mother nature by removing it.

 

You should be showing a code if they are blocked.