exploding catalytic converter?

I have a 98 Blazer 4.3L that sat for 18 months in a police impound lot. When I got it back, it wouldn't start. Thanks to this forum, I figured out I had a weak fuel pump. After I changed the pump, the truck came back to life. But now she's still alittle sick. When ever the truck is running, from start up to shut down, I get a type of detonation sound from the cat. The popping gets worse the longer I drive it.

So I took it to a muffler shop the have it replaced. The mechanic told me I have a stuck valve instead and he wouldn't change the cat. Ok, so how do I determine what it is? Let me share what I've observed so far. When I first got it started I smelled rotting eggs(but not since), my gas economy and the power of the eng is way down, high rpms with no increased speed when driving, and my check engine light is on. After one of my drives around the block(and some highway miles) I looked at my cat. It appeared to be the same color orange as molten metal inside a blast furnace. Is that normal?

What does it sound like to you guys, a stuck valve or blocked cat? Could a stuck valve cause the cat to overheat like that? If it was a $50 part, I would go with my gut instinct and change it. But since it is over $400 (the cat) I would like to get a second opinion first.

Sounds like a clogged cat. to me

Plugged up cat, had the same thing on my 87 Dodge Aries. BTW, this will lead to burn exhaust valves, get that changed or off at least.

It sounds like a clogged/restricted cat or very rich mixture. Remove an upstream O² sensor (or both) to relieve pressure and see if the problem repeats in a short test drive. There will be trouble codes set with the sensors removed, but you should be able to determine if the cat is plugged.

What kind of valve?
Did they run a back pressure test?
Is engine missing?
For a quick plugged cat or exhaust system check.
Hook up a engine vacuum gauge to engine and check vacuum at idle and at 2K RPM.
If vacuum drops at 2K from idle your exhaust system is plugged.

Engine not running right will also heat up exhaust system cheery red.

A glowing cat means you are running rich. Your Sertvice Engine light is on, that would be the first place to start. Get it scanned or scan it and see what fault codes are showing up. You need to get the Service Light figured out and go from there. It could be a clogged cat(kinda sounds like it), but you have to start with the codes first.
Good Luck!

Thats all he said was a valve, I assumed he meant an exhaust valve, unburnt fuel igniting once it hit the cat. As far as the codes go, I took it to another mechanic and he could not get a reading. He said there was no power at the plug so his scanner wasn't reading. I was going to start another thread on that one later instead of bunching together with this one. It doesn't sound like the eng is missing, it runs rough, a slight vibration at idle. The popping sound is not constant, there might be one every 3 sec, then 2 in a row, then 5 sec later, then ect.... I might try taking off the o2 sensor and see what it does, I was going to disconnect the whole thing and run an open pipe( no cat, no muffler) to see what happens. Do you think that would be a good idea? What was that about a vacuum check, where do I connect the gauge to?

Thats all he said was a valve, I assumed he meant an exhaust valve, unburnt fuel igniting once it hit the cat. As far as the codes go, I took it to another mechanic and he could not get a reading. He said there was no power at the plug so his scanner wasn't reading. I was going to start another thread on that one later instead of bunching together with this one. It doesn't sound like the eng is missing, it runs rough, a slight vibration at idle. The popping sound is not constant, there might be one every 3 sec, then 2 in a row, then 5 sec later, then ect.... I might try taking off the o2 sensor and see what it does, I was going to disconnect the whole thing and run an open pipe( no cat, no muffler) to see what happens. Do you think that would be a good idea? What was that about a vacuum check, where do I connect the gauge to?

Connect a vacuum gauge to main engine vacuum.

If you have a miss vacuum will also be low or flickering.
You can drop[ the pipe for a exhaust system plugged test but.
You need to fix engine running first thing.
A miiss will plug or overload cat.
Does check engine light come on key on?
If no power to test plug check fuse.
Good Luck
MT

Alright, got it fixed. One of my problems was I wasn't able to read codes w/ a scanner. Found a bad wire that supplies power to the obdII port. Got that fixed code was the dreaded p0300 multi/random misfire. I checked sensors, (map, o2 ect) sprayed water around vacuum connection while eng was running, nothing everything was tight. When I first got the truck back I replaced the cap(twice first cap was giving a weak spark between #4 + #5), rotor, wires and plugs. All ACdelco, I've heard it enough on this site to go w/ the good stuff. Replaced all that stuff again based on a guess and desperation. It worked, ran for ten min. no code, no glowing cat, and no backfire. Test drove it and got my power, gas milage, and my pride back. Thanks to everyone for your help.

You are welcome and thanks for posting back how it went and what it was.
Job well done.
Glad all is well and running good now.
Good Luck
MT