# Catalytic Converter Clogged?



## mojob

What are the symptoms of clogged cats? I was told by my transmission shop that mine were clogged. I trust the guy because he wasn't going to be replacing them, but I want to get a second opinion before spending over $500. I've noticed my truck seems to be lacking power and is a gas hog. It's a 98 GMC 3500 with a 454 and has 84K miles. Anybody else been through this?


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## Northland

I had to replace the one on my truck. It made world of difference.

My truck was WAY underpowered. I would step on the gas and it would accellerate and then after about a second or two it would fall flat on its face and just be sluggish.

I was quoted between $600 and $800 for the piece. I bought an aftermarket Dynomax cat on ebay for $60 andhad it installed. WOrks great. Someone told me not to put an aftermarket on on, they said it would mess witht the computer...but I havent had any problems yet. Just make sure you get the right cat.


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## Robhollar

Find a shop who has a back pressure gauge. They can check and see if you have to much back pressure by taking a precat O2 sensor out and installing the gauge. If its clogged it will show on the gauge....Rob


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## Buster F

I recently had a clogged converter on one of my trucks. The truck wouldn't rev past 2500, was way underpowered, and the converter would glow red hot at night. Hope this helps, Roy


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## Oshkosh

*No Power ,poor mileage....*

Lack of power,Poor mileage,nothing or very little coming out the tail pipe,A Rattle in the exhaust.........I have had my converter replaced by local a shop(Lou's Custom Exhaust) in two vehicles for $150 each Installed, that is with a high flow cat fully welded in....Dont pay $600- No need to anymore...
When I purchased my F150 4x4 it needed a trans, the reason why was the previous owner had driven it with a clogged cat for a while...As it lost power he just gave it more gas and the trans tried to compensate...Turned the torque converter blue and not Ford blue either...Lets just say there was no need for it!!!


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## DeereFarmer

Oshkosh: how was your experience at Lou's. I get all my exhaust work done at one of their sister shops in Waltham, MA and they are great. I have been to 4 of them with friends and such before and never had any issues. Always first class work and people. You probably went to the one in Manchster, right? $150 beats what the dealer would charge and it is just as quality work if not better. That si the route I would take mojob if you do have a clogged one.


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## Oshkosh

*Nothing but excellent work...*



First Time Out;345533 said:


> Oshkosh: how was your experience at Lou's. I get all my exhaust work done at one of their sister shops in Waltham, MA and they are great. I have been to 4 of them with friends and such before and never had any issues. Always first class work and people. You probably went to the one in Manchster, right? $150 beats what the dealer would charge and it is just as quality work if not better. That si the route I would take mojob if you do have a clogged one.


 I have nothing but praise for Lou's.....First class all the way.
They bend the pipe up for the best clearance, weld all the connections all heavy aluminized or even stainless if you want,very consistent on their pricing...do it while you wait......Most importantly they stand behind their work...
I've had two systems done there and both where great.
Route 1 in Peabody actually was one and North Reading was the other store that I dealt with...
Hard to find guys like that anymore....


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## bigskytom

*Quickest way to tell if converter going*

If you bang on the converter and hear it rattle, it is going out. I would suspect you should get a "check engine light" or "service engine soon". You are in the mileage range for replacement. You might have your mechanic check and be sure the injectors are operating properly. I had one fail due to faulty injector, dumping too much gas in the system.


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## Northland

Oh yeah... 2 other things...

Check with the dealer. I think gm warranties converters up to 80 or 85k miles...cant remember which. 

Also tell whoever repairs it to give you back your old converter. There are many places that will buy them from you to get the platinum out of them. If you tell the muffler shop this they may knock 25-50 bucks off the price just to keep the old converter.


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## GA73

buddy is getting a po420 code. dealer said tthat it means the cat is bad


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## mojob

Thanks for all the replies. I might be in luck. I took it to the dealer for a bad fuel pressure regulator. It was causing a rich mixture, which Bigskytom said might clog the cats. Getting this done under warranty would be too cool. I wouldn't of even thought of this if it weren't for you guys. Thanks!


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## jpboost

*Signs of clogged cats?*

Well here are some signs when your cats become clogged 'coz I have the same experience with my Volvo catalytic converter. Well here it goes--A good sign of a bad catalytic converter will be a sudden decrease in performance and a noticeable decrease in fuel economy. A clogged catalytic converter traps exhaust gas in front of the catalyst, which then creates back-pressure that prevents your engine from breathing properly. Your engine may also suddenly quit after a few minutes of driving with an increased back-pressure. It makes the engine feel like it is starving for fuel. Another sure sign that your catalytic converter is bad is when you can hear rattling noises emitting from the catalyst. Sometimes you may actually hear a whistling sound when the throttle is applied indicating a restricted exhaust flow or catalytic converter problem. This rattling may also be noticed more when the car is not doing anything while the engine is running.


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## davidrbean

Northland;345795 said:


> Oh yeah... 2 other things...
> 
> Check with the dealer. I think gm warranties converters up to 80 or 85k miles...cant remember which.
> 
> federal emissions requires computers and convertors to be warrented for 8yr/80k miles so you are out of warrenty. chech with walker they have converters to fit the truck


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## davidrbean

p0420 code goes with the cat on the drivers side if you have that code most likely the cat has failed


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## oakvillerex

On GM's P0420 is a catalyst efficiency low code which is usually a bad cat. On newer vehicles (GM especially) the replacement converter has to be within a 5% efficiency difference to an OEM cat or you will get P0420 again.


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## icebladez

Also remember that a bad Cat converter usually is accompanied by a rotten egg smell,from tail pipe.


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## QuadPlower

I'd tell them you wanted the cat back, but most places charge a core charge for them just so they can then turn them in.

Check aftermarket. There are a lot of HIGH Flow converters that will really bring that 454 to life. If there are two, then you would have to replace both of them.


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