Does this sound like a bad Catalytic converter?

 99 Honda Accord with 200 K on the clock. Gutless. Mileage has dropped about 4 mpg. Sitting in park if I slowly increase the revs it’ll only go to 4500 and hunt down to three grand and back to 4500. If I quickly try to increase the revs it bogs down and barely makes it to 3k. I could hear rattling under the car as I rev the engine. I removed the heat shield from the  converter and when I tap on it I can hear rattling. I don’t think it’s coming from any other part of the exhaust. Will pulling  the oxygen sensor help in  diagnosing the converter? 

I'm not sure if the cat is bad but I had a similar rattle in my CRX. Given the mileage (400k miles) on the car, I was 100% convinced it the substrate was breaking up. I pulled the entire exhaust system off the car and found this in the cat:

That was the source of the obnoxious rattle. The cat looked great; not clogged and the substrate grid was intact.

I replaced the O2 sensor a few days after that.

The cat sounds like a good candidate from your description. My wife's van had the same issues, except the hunting RPMs, and with a cat efficiency CEL, new cat did the trick.

Pulling the 02 sensor and revving the engine should tell the tale.  A pressure gauge screwed into the sensor hole completes the diagnosis.

Streetwiseguy said:

Pulling the 02 sensor and revving the engine should tell the tale.  A pressure gauge screwed into the sensor hole completes the diagnosis.

What pressure am I looking for at the sensor?

easy test, unbolt the exhaust and let it run. You do not even need to drive it, just let it idle and see if it loads up

A smart mechanic will not waste time messing with rusty exhaust bolts if it's not necessary.

The easy button test for this problem is to connect a vacuum gauge to the motor and observe the vacuum at idle and at higher RPM.

With a plugged exhaust the vacuum will decrease as RPM raises.

Normally it will increase.

In reply to rustybugkiller :

Nothing at idle.  4-5 psi accelerating is about max. If the cat is plugged, you will break the needle.

bentwrench said:

A smart mechanic will not waste time messing with rusty exhaust bolts if it's not necessary.

The easy button test for this problem is to connect a vacuum gauge to the motor and observe the vacuum at idle and at higher RPM.

With a plugged exhaust the vacuum will decrease as RPM raises.

Normally it will increase.

I’m thinking it’s not the cc. Vacuum test holds steady. I’m looking elsewhere. Just odd no codes

Streetwiseguy said:

In reply to rustybugkiller :

Nothing at idle.  4-5 psi accelerating is about max. If the cat is plugged, you will break the needle.

No change with o2 sensor removed. 

Wait,  I have a sticking gauge. When at idle I have 20 inches of vacuum give it revs it drops to zero never recover his past 7 inches. Comparing to the Miata the gauge drops to 5 inches and immediately goes to 25. So I think my converter is bad in the honda

Yep, converters shot. Dropped one end and revs like a mudder. 

Thanks everyone

rustybugkiller said:

Streetwiseguy said:

Pulling the 02 sensor and revving the engine should tell the tale.  A pressure gauge screwed into the sensor hole completes the diagnosis.

What pressure am I looking for at the sensor?

Any at all.  More than 1psi is suspect.

From your description, it'd probably peg a 15psi gauge with light throttle application.  I'd want to check pressure after the cat too, to make sure it's not something less expensive like a muffler broke up and flapped itself shut internally, which also happens.

converter is melted on the intake side. For some reason my pics aren’t working. 

Now you need to figure out why it melted.  

In reply to Streetwiseguy :

The only time the cel came on was for the knock sensor. When I did the TB I had the cam one rib off for awhile. 

In reply to Streetwiseguy :

200,000 miles, I think it is allowed to melt

In reply to mad_machine :

Nope.  Melted is bad, no matter the mileage.  Plugged with something, ok.  Melted, no.

Material covering the inlet screen (honeycomb) looked like melted solder. 

Would burning a quart of oil every 2k cause this? Cam timing off? I haven’t noticed it running rich. No smell

Take out the o2 and rev it. If it goes to redline you're onto something. If it still doesn't rev up you're more likely looking at a fuel pressure issue. 

Over fueling or not burning the fuel causes Cat Convertor to melt down.

A steady misfire will do it.

Nothing like that on my watch but it’s been sluggish since I’ve owned it. Who knows what happened with the PO.