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possible bad cat?

This is a discussion on possible bad cat? within the Internal Engine forums, part of the LSx Technical Help Section category; I was driving my car today and the change oil light came on. I had just changed the oil about ...

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    possible bad cat?

    I was driving my car today and the change oil light came on. I had just changed the oil about 3 weeks ago so i thought nothing of it especially that it went right out. I got to my destination about 5 more miles down the road and the car started to idle extremely rough, after a few minutes it stopped. I pulled out and started to drive home and the whole car was shaking terribly as if i had a flat tire. I checked and of course i did not have a flat. I pulled over and popped my hood and the whole motor was rocking back and forth as if there was an imaginary person jarring it back and forth. I check the exhaust and there was almost no exhaust coming out it was just sloooooooowly coming out. I tried to continue on my ride home and the car had almost no power whatsoever and i started to get a little bit of a rotten egg smell. BTW the SES light also came on. The car had 2 or 3 cats replaced before i bought it. Does it sound like this cat is shot or clogged and that i may need a new one? In this case would i be better just getting a hi-flow, and if so how much does a cat or a hi-flow cat cost, as i am having trouble finding prices.

    Oh yea i wound up having the car towed home.

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    Member keliente's Avatar
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    99 Firebird Formula

    If the SES light came on, get the codes read. If you don't have something to read it with, AutoZone will scan it for free. From there you should be able to diagnose your problem easier...it does sound like a clogged cat could be your culprit. You car may be running excessively rich, you mentioned 2-3 cats being replaced before you bought it...I think a high-flow cat (or none at all) and a good tune should keep you set for quite a while.

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    i'm going tomorrow to get the code read at a shop i deal with, they are pretty good guys. The previous cats were all put in before i bought it. Anyone know how much a hi-flow is?

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    just did a general scan on the car and the P0300 code for engine missfire came up. It didn't say why or anything more than that. So tomorrow i'll take it and see what the shop says.

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    Senior Member Hurley711's Avatar
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    got the car scanned today. they said cylinder 2 is misfiring so bad it's almost inoperable, and the rest of the cylinders are misfiring occassionally. I'll start with plugs and wires, if that doesn't fix it i'll go to coils, hopefully i don't need to go to valves. The car doesn't smoke at all so hopefully i don't need valves. What do you guys/girls think is the most likely cause?

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    I know you said that the car doesn't smoke but does it burn oil? How do the plugs look?

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    the car doesn't burn oil, and i haven't checked the plugs yet.

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    checked the plugs and wires. the plug for cyl 2 the one that was the most problamatic was dry, so i'm guessing it's not the valves. The seat of the plug had dropped a little and the wire looked coroded. We pulled the seat of the plug up and cleaned the ends of the wire as best we could. Put it back in and the car ran much better for about 2 minutes untill i got it back on the road then it started acting up again. So i'm guessing i need new plugs and wires. Sound about right?

    also did a pressure check on cyl 2 and it was fine.

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