trying to diagnose possible cat issue.

[snidehockey]

OK here's where I'm at...got this 00 gt bout 2months ago...dealer didn't list the mods...but so far i've found bbk cai, BB throttle body, PI upper intake manifold I THINK - long tubeheaders, bbk h pipe W/ cats, and I dunno what the exhaust is but its aftermarket.

So when the car warms up and its under load at about 2 to 3k rpm in 3rd 4th or 5th gear it rattles like CRAZY what sounds to be beneath either the passenger floor, or the center of the car.

I got 2 huge hose clamps and torqued those suckers around the passenger cat to rule out a heat shield rattle and that didnt work. When I tap the cat w/ a mallet no rattle at all.

My 2 guesses here are either the passenger cat is clogged (console area gets just a little warm sometimes) OR the clutch cable heat shield that someone described (I don't know what it looks like though)

This rattle is really obnoxious when I pull out of a toll booth or something so its definitely audible from outside the car, and it does do it in neutral but not nearly as loud...in fact u have to be laying on the ground next to it to hear it.

ANY input would be cool! thanks

 

[Miles]

What can sometimes happen is the material within the catalytic converter actual wears down / deforms into a ball and rattles around in the cat chamber - this is more common in high exhaust air flow like our V8's. Would explain why under load it is louder (ie. more airflow pushing the ball of material around inside the cat chamber).

This is why I went with a steel core cat converter on my setup.

How to test for this? Hmm.. get something that vibrates and press it up against the cat to see if you can hear something rattling inside (hand sander, maybe tap it with a soft mallet?)

Good luck

 

[streetstang03]

... PI upper intake manifold I THINK -

i'd hope so since its a 2000

 

[snidehockey]

oh all the 2000's have em? Makes sense now! thanks for the replies...I hit it w/ a mallet and didn't really get any feedback from it...I hope this isn't one of those things that is always there til I sell the car...I'd have no problem getting a catless H or X but I'd be somewhat convinced that it would kill this rattle before I do. You guys think of I got th car to make the noise for an exhaust or muffler shop they could say if it was cat or not?

 

[MyStangGT]

Next thing to do is pull the mid pipe off and shake it. If it rattles get a long rod, screwdriver or whatever and beat the stuffins out of it. Do both sides if you take this route.

 

[snidehockey]

Next thing to do is pull the mid pipe off and shake it. If it rattles get a long rod, screwdriver or whatever and beat the stuffins out of it. Do both sides if you take this route.

yeah I've really considered this for a few days now...I will probably end up doing that. I'll need a MIL thing though won't I? It''l throw a CEL if not.

 

[Miles]

yeah I've really considered this for a few days now...I will probably end up doing that. I'll need a MIL thing though won't I? It''l throw a CEL if not.

Without cats you will eventually throw a CEL code. An exhaust shop should be able to diagnose the problem for you.

Thanks goodness for steel core cats (damn emissions - well actually my car sounds 10x better with cats on than no cats)