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Old 03-16-2010, 07:10 PM
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Plugged Cat

I have 1999 GMC 1500 4x4 5.7l 350 and my cats are plugged. I'm wanting to know if i have to replace them due to the computer or can i just stick mufflers in place of them.

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Old 03-16-2010, 09:32 PM
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Do 99s have down stream(after cat) 02 sensors? If so you will have to run O2 Sensor emulators/simulators
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Old 03-17-2010, 06:04 AM
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If I were you, I'd do some high flow cats,
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Old 03-17-2010, 06:56 AM
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Ayuh,... If you Don't have the downstream O2 sensor,...
Pull 'em off,+ pound a bar through 'em,+ knock the junk outa 'em...
Then put 'em back on Empty...

That way it'll pass any Visual inspections with flying colors...
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Old 03-17-2010, 09:16 AM
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1999 will have OBD II and will have down stream sensors. IF you have no sniffer testing, you could get by without but would have to use simulators. Of course that is not legal.
As mentioned by Rickracer, replace them with high flow's.
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Old 03-17-2010, 10:19 AM
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first find ou why they melted as you'll be wasting your money putting the new ones on there as they will plug out too. ussually what causes it is too rich of a fuel mixture causing them to over heat , or someone running racing gas that has lead in the system , if th truck has less than 100,000 miles on it the dealer has to replace them by federal law ( its in the epa website )
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Old 03-17-2010, 01:27 PM
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Quote:
Originally Posted by stimpy
.... if th truck has less than 100,000 miles on it the dealer has to replace them by federal law ( its in the epa website )
This is true, but I'd bet they will figure out some way to wangle some money out of the OP somehow, either by testing to be sure they are clogged and deciding they are not, or some other scheme. I would be very sure of the criteria used to determine whether they are clogged or not, and be prepared to answer some questions as to how they got that way. Clogged cats are not all that common these days, and usually have been accompanied by oil consumption or driveability problems, (like a chronic misfire or something similar). Stealerships aren't the friendly places they once were.
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Old 03-17-2010, 03:15 PM
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I may be wrong but, I believe any vehicle with a cat built since 1995 has to be covered for 8 years or 80,000 miles as mandated by the EPA.

A quick search validated my comment.
From the EPA site:
"There are three specified major emission control components,
covered for the first 8 years or 80,000 miles of vehicle use on 1995
and newer vehicles:

* Catalytic converters.

* The electronic emissions control unit or computer (ECU).

* The onboard emissions diagnostic device or computer (OBD)."
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Old 03-17-2010, 04:20 PM
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Quote:
Originally Posted by CAMO KING
I have 1999 GMC 1500 4x4 5.7l 350 and my cats are plugged. I'm wanting to know if i have to replace them due to the computer or can i just stick mufflers in place of them.
I would get a second opinion on that diagnosis. Those don't really plug. They usually set a code for "cat efficiency low". And both to plug or fail at same time is strange also.

If there's a low engine power problem, hopefully someone would of spent some time diagnosing it instead of seat of the pants guessnosis

Those cats are very expensive and cheap after market will probably set check engine light after a bit.

And like mentioned already, there may be a reason why they have failed other than being old. Bad fuel mixture, misfires and things like that.
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Old 03-17-2010, 04:36 PM
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Quote:
Originally Posted by 1ownerT
I may be wrong but, I believe any vehicle with a cat built since 1995 has to be covered for 8 years or 80,000 miles as mandated by the EPA.

A quick search validated my comment.
From the EPA site:
"There are three specified major emission control components,
covered for the first 8 years or 80,000 miles of vehicle use on 1995
and newer vehicles:

* Catalytic converters.

* The electronic emissions control unit or computer (ECU).

* The onboard emissions diagnostic device or computer (OBD)."
good to know, now used to be 100K
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Old 03-17-2010, 04:55 PM
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I your looking for a culprit check the EGR, seen failure there cause problems in other parts of the system
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Old 03-17-2010, 09:41 PM
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Quote:
Originally Posted by stimpy
first find ou why they melted as you'll be wasting your money putting the new ones on there as they will plug out too. ussually what causes it is too rich of a fuel mixture causing them to over heat , or someone running racing gas that has lead in the system , if th truck has less than 100,000 miles on it the dealer has to replace them by federal law ( its in the epa website )
This is the best advise in this thread
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