bad cat symptoms

[tkhilliard]

what are some major signs of a bad cat? i gotta 02 gp gt and noticed its rough running somtimes, and dies sometimes when i start it. wondering what the "flacky cat" symptoms are. after its on it seems to run smooth but almost feels like it misses, and not quite as peppy as it used to be

[BNaylor]

Various symptoms depending on how bad the CAT convertor is clogged.

Engine dying after starting.

Misfires but no SES light and no codes.

Misfires with SES light and P030X misfire codes.

Engine runs OK until you get around 4000 rpms, then misfires or cutout.

Poor acceleration and driveability.

Poor fuel economy.

Transmission does not shift correctly.

The dealer can run an exhaust backpressure test with a low pressure gauge or a regular vacuum test. Since you have a '02 you might get it checked out.

[Niq]

I'm a 02 myself. Can you give a guess-timate at how miles this problem usually shows up? This sounds like something that will happen, instead of “might happen.”

If it does, I'll probably have a High flow cat put back in. Which I'm sure cost big $$$.

[Langning]

Originally Posted by Niq

I'm a 02 myself. Can you give a guess-timate at how miles this problem usually shows up?

My 01 GT's cat converter clogged this June with only 48,000 miles on it. Initially I attributed it as transmission problem. My car drove very slow and no acceleration but once it got to cruising speed, it ran fine. Just that it took forever to start from a dead stop...

Short after the dealer replaced it free of charge I recieved a GM letter that the warranty is extended to 120,000 miles...

[BNaylor]

Originally Posted by Langning

Short after the dealer replaced it free of charge I recieved a GM letter that the warranty is extended to 120,000 miles...

Whatever you do hold on to that notice letter from GM. If your CAT fails again before 10 years or 120K miles, whichever comes first, you will be entitled to another CAT convertor free of charge.

I have a 2001 Regal GS in a similar category and still waiting for the problems to start. So far it runs like a champ but it is just like a ticking time bomb knowing that GM delivered those years with known bad CATs. It is nerve racking but it is nice to be assured that the problem will be covered.

BTW - The original CAT failed in my '97 GTP at 82K miles but that was way before GM ever acknowledged there were CAT problems. I replaced it with a Magnaflow Hi-Flow CAT and it is one of the best mods I ever did.

[mike561]

would another symptom of a bad cat converter be a loud rattleing/clunking noise comming from under the car also?? my dad's 00' blazer is doing that and it got me wondering...

[BNaylor]

Originally Posted by mike561

would another symptom of a bad cat converter be a loud rattleing/clunking noise comming from under the car also?? my dad's 00' blazer is doing that and it got me wondering...

It is possible to get that type noise from a CAT. Also check for any visible damage to the CAT or exhaust system if you have an SUV you take offroading. Another symptom is a funny smell like burning plastic. Another is the CAT will glow cherry red indicating temperature exceeding the standard 1200 degrees F.

[mike561]

yeah i kinda figured it might be, ill give the underneath a look and see if it is glowing red and for any other obvious damage, thanks again.

[tkhilliard]

cool, thanks, i got about 6 of the 7 symptoms bnaylor3400 symptoms. gonna call and get the thing checked out.

[tkhilliard]

i should read my reply before i hit post huh? symptoms u listed, is what i meant