Bad cat

What are the symptoms of a bad catalytic converter?
I have noticed for a while now, that my car has lost power
I changed the wires and spark plugs thinking that, that was my problem
I don't have the engine light on, would a clogged cat turn my engine light on
I have a 2005 comp g

Loss of power is a common symptom of a bad cat, but other things can do the same; fuel pressure, dirty MAF sensor, vacuum leaks and old ignition system components can create the same problems.

An easy way to test (from one of our mods in the forum) for a clogged cat is to floor the gas pedal from a stop, if the car shifts to 2nd gear, then the cats are likely OK; if it keeps revving up and refuses to shift, then there's probably a blockage in the exhaust system and further inspection is needed.

There's 2 other ways that I'll describe next.

Using a vacuum gauge:

Connect the gauge to a suitable vacuum port BEHIND the throttle body. Watch the needle and take note of the reading, now raise the rpms to 2500 and look at the gauge, it should be slightly higher than at idle. If it starts moving down to 0 there's a restriction in the exhaust.

Using OBD2 live data:

Check the reading of the map sensor with key on/engine off (anything between 24 and 29.9 inHg depending on your elevation), start the engine and compare the reading, it should be a lot lower than before (around 9 inHg). Now raise the rpms to 2500 and watch the reading, it should be lower than at idle; if it starts going up to the reading at KOEO the exhaust is blocked.

Oscar.

I will try the first option
I don't have a vacuum gauge and don't know if I can rent one from a auto parts
And about the OBD2 don't have one of those either
All I have is a actron CP9580

Vacuum gauges are cheap, about $20.

That scanner supports live data, just go to the option and look for the MAP sensor reading.

Oscar.

Ok, thanks
Its probably going to be in a few days cause at this time I am replacing the manifolds
I was thinking just to take the cat off and not put one on
We don't need to have one here

Ok, so I decided to replace my headers and not just the cat
Everything went ok, but
When I put the car in reverse it idles ruff, when in drive it runs perfect
I looked and looked and looks like everything that I unplugged is plugged in
Any ideas
Thanks