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Pontiac of the Month

Pedja's 1968 Firebird

2019 March
of the Month

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Engine revs while driving, then won't go above 60mph, catalytic converter question.


Hello everyone. Happy 4th of July to you all. I got a not so good 4th of July present a few days ago. I own a 2002 Grand Prix GT with 198,000 miles on it. Automatic Transmission It's my baby and has never let me down before, besides general standard maintenance, it has been great. I love this car. Anyways over the last few months we have noticed that you can hear the engine a lot more clearly. Not being car people at all we thought maybe it could be a hole in the muffler. Well, the service engine soon light came on and as it was only a few hundred miles away from it's next oil change so we decided to take it in. We asked the guy there if it was the muffler and he said it wasn't and that we had a hole in the catalytic converter.

We were on our way home(it's roughly 30 miles) and all of the sudden the engine started revving from 2rpm up to 3rpm and kept doing this the whole way home. And when I tried to press on the accelerator it wouldn't go above 60 or 65 mph, and sometimes wouldn't accelerate at all. And at stop lights while idle the engine just kept revving. We made it home and I looked up catalytic converters and it says it's an emissions control device, and the could possibly explain why we've heard a general increase in the loudness of the engine. But would that explain why the engine would be trying to rev the whole way home and not go above 65 or even accelerate when I stepped on the accelerator?

I took it out for a drive this morning, and it seemed to be fine when I accelerated and the engine did not try to rev itself and the service engine soon light isn't on anymore, but the engine is still very audible. My wife was like "maybe it self corrected itself", but it didn't seem like a self correcting problem to me. Could this all really be because there is a whole in the catalytic converter? I looked up replacement cats for my car and they seem relatively cheap. I am hoping it's this. Or could it be something more serious like a transmission problem? I was wondering if any of you have had this problem or heard of this problem and possible suggestions to fix it? I am willing to shell out of few hundred bucks but wouldn't want repairs in the thousands. I'd get a new used car, in that case, of course, a Pontiac! Thanks in advance.

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  • 1

To me it sounds like a failing cat converter.  If you crawl under the car with a rubber mallet tap on the cat.  If you hear ball bearings in a pop can then the media inside the cat is falling apart.  The other thing it could be is a plugged converter.  The only way to tell is to pull the cat off and inspect it.  It would look like a solid lump of charcoal.


Good luck.

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  • 0

you could always just take it on the freeway from a slow starting speed then stomp on the gas pedal and if you see smoke out of the tail pipe its clogged.

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