Blocked precat and cat, poor performance *solved

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sjacoby
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Blocked precat and cat, poor performance *solved

Post by sjacoby »

I recently cut out my blocked pre-cat and temporarily clamped a flexible exhaust pipe in place of it. It was leaking pretty bad, so today a muffler shop welded a piece of pipe in place. It is very quiet but is running like it was before with a plugged pre-cat. Does it take time for the computer to learn the new exhaust in absence of the leak? What do I do to make it run smooth again. It will not accelarate or shift on the highway
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Re: Took out blocked pre-cat and welded in pipe, poor perfor

Post by HenryJ »

Did it start running worse once you sealed up the exhaust leaks? Did the main cat plug up now too?

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Re: Took out blocked pre-cat and welded in pipe, poor perfor

Post by hootz »

Sounds like you still have an exhaust restriction. An easy way to check for a restricted exhaust is to use a vacuum gauge. Find a vacuum port that has full vacuum at idle (some ports are ported and the vacuum increases as the rpm increases). With the engine idling in park, observe the vacuum gauge reading. I would expect about 17 inches of vacuum (give or take a few inches) at idle in park. Increase the rpm to about 2,500 and watch the gauge. Normally you would expect the gauge to stay the same or maybe increase a little with the transmission in park. If the gauge falls significantly when the rpm is increased you most likely have a severly restricted exhaust.
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Re: Took out blocked pre-cat and welded in pipe, poor perfor

Post by riceburnr2005 »

maybe whatever was in you're precat fell back into the main??
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sjacoby
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Re: Took out blocked pre-cat and welded in pipe, poor perfor

Post by sjacoby »

Thanks for your responses, ya turns out it was the main cat as well, replaced that at a muffler shop and they didn't require me to put in a new Y pipe and pre cat thank god. Runs like a dream now, forgot the power that I once had.
Thanks again
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Re: Took out blocked pre-cat and welded in pipe, poor perfor

Post by HenryJ »

Glad it is back to normal.

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Re: Blocked precat and cat, poor performance *solved

Post by riceburnr2005 »

that's what we're here for!!
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2003 CC LS, indigo blue, Spectre Cold Air, OBX throttle body spacer, descreened MAF, hunter bull bar, BAJA off road lights, 15x7 Crager soft 8 wheels, 31x10.50x15 Goodyear Wrangler Authority tires, cranked TB's, Daystar 2 inch shackles, 2" PA body lift, 1.5 inch spacers in the rear, Access TonnoSport Tonneau cover, reese hitch, carbon fiber front chevy badge, Lund bug deflector, roof rack from a blazer, Kenwood CD player, JVC 6 1/2 speakers.