Would a car with 100k benefit from new cat convert

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PhillyJoe

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2007 Grand Prix GT, 3.8l supercharged. Just turned 100k. Seems sluggish, not sluggish all of a sudden, but it doesn't have the pop it had when new. Plugs and wires were changed at 90k. When I step on the gas, it doesn't respond like it should. Some people have said the catalytic convertor may be partially clogged.
AAP has a MagnaFlow direct fit stainless steel cat convertor for $238. (A Walker D/F was similarly priced at $259).I entered HUGE50 which I found on BITOG and it's now $188 with free shipping. Have to think it may be near the end of its useful life and a new cat might actually improve things. Two bolts up front and 2 in back shouldn't cost an arm and a leg to install. Seem like a plan or don't fix what ain't broke?
 
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I've used the Magnaflow OEM grade cat on my 03 CRV, which I had to get shipped to out of state, because of California's stupid CARB laws and have had nothing but problems with it. I took it in for a smog check and barely passed. With less than 3,000 miles on the cat, I was tripping the P0420 code for a bad converter. Magnaflow makes some beautiful looking exhuast and the stainless with mandrel bends is really nice, but the guts of their cats are a different story. I installed a new factory cat which cost me almost $1,500.00 but have had no problems with over 10,000 miles on it and all of this is with the original 02 sensors.
 
I'm thinking that if the cats were this severely clogged, you would get error codes stored in the ECU. Are you getting any?

How is your fuel economy? If it's not as good, maybe your O2 sensors are on their way out?

What's the condition of the air filter?
 
The situation you describe could be a number of things. Don't go blindly replacing things (especially spendy things) without a good reason. You'll end up with a new engine in an old car, an empty wallet, and it still won't run right.

That being said, I don't know too much about this engine.
 
I think your OEM cat is better than most aftermarkets.It could be you are just use to the power of the car now.I would try some redline,clean the TB MAF things like that first.If your still not happy there is always a smaller pulley,CAI,exhaust mods or have the PCM reflashed.We have used many aftermarket converters and many of them will still give PO codes.
 
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Doesn't anybody diagnosis a problem before randomly changing parts? I have suggestion; buy a new engine, that will fix your problem.
 
Originally Posted By: Vikas
Doesn't anybody diagnosis a problem before randomly changing parts? I have suggestion; buy a new engine, that will fix your problem.

The sad part is, it might not. (I'm furthering your point)
 
I wouldn't rush to replace it. You could spend your $188 plus shipping, tax, and installation, and be worse off, since many aftermarket cats have shorter life expectancy than OEM.
 
Originally Posted By: Kool1
I've used the Magnaflow OEM grade cat on my 03 CRV, which I had to get shipped to out of state, because of California's stupid CARB laws and have had nothing but problems with it. I took it in for a smog check and barely passed. With less than 3,000 miles on the cat, I was tripping the P0420 code for a bad converter. Magnaflow makes some beautiful looking exhuast and the stainless with mandrel bends is really nice, but the guts of their cats are a different story. I installed a new factory cat which cost me almost $1,500.00 but have had no problems with over 10,000 miles on it and all of this is with the original 02 sensors.

Your problem may have been caused by using a cat that was not compatible with your emission system. If it was originally a California car, it may have come with a special emissions package to meet CARB requirements. I know my Burb has such a system. Magnaflow has two high flow cats systems that physically fit my Burb: one that is not compatible with the CA emissions package (not shippable to CA) and one that is compatible (and is shippable to CA). The compatible cats cost $300 more, IIRC, which is probably because of different precious metal composition.
 
Originally Posted By: Quattro Pete
I'm thinking that if the cats were this severely clogged, you would get error codes stored in the ECU. Are you getting any?

How is your fuel economy? If it's not as good, maybe your O2 sensors are on their way out?

What's the condition of the air filter?

This. If nothing else, remove the O2 sensors, attempt to clean, and re-install. I would replace both O2 sensors before replacing the cat.
 
Originally Posted By: Kool1
I've used the Magnaflow OEM grade cat on my 03 CRV, which I had to get shipped to out of state, because of California's stupid CARB laws and have had nothing but problems with it. I took it in for a smog check and barely passed. With less than 3,000 miles on the cat, I was tripping the P0420 code for a bad converter. Magnaflow makes some beautiful looking exhuast and the stainless with mandrel bends is really nice, but the guts of their cats are a different story. I installed a new factory cat which cost me almost $1,500.00 but have had no problems with over 10,000 miles on it and all of this is with the original 02 sensors.
that's why California is so stringent about replacement cats. As for the original post. The car is certainly due for 02 sensor's. Id put in new oem ones and see how it runs.
 
Dont replace these GM 3800 cats with some cheap aftermarket one, they have major problems.
Eastern cat even has a special high content cat (read expensive) just for these applications.

Look for the obvious, then try a PEA based fuel injecor cleaner. It may have dirty injectors at 100K.
These are Delphi grey 44lb units IIRC. Clogging is not unheard of with these.
 
Is it still making the same boost levels?
If the exhaust was clogged boost would go higher i bet.
 
Originally Posted By: Vikas
Doesn't anybody diagnosis a problem before randomly changing parts?


No, that requires ability to read a shop manual and follow flow charts. It is amazing how many shops call into parts dept and base their whole diagnosis on "do you guys sell a lot of these?"
 
Don't do it. I assume you have to pass an OBD-II inspection. At a minimum wait until 120k; OE cats have a lengthy warranty up to 100 or 120k depending on year.

You can run a backpressure test on your front O2 sensor port to see if you really DO have backpressure. If you remove your muffler it won't sound super raspy with a clogged cat.

I had a piece of cat come loose and lodge itself sideways like a golf ball sized "death star" in the rear of the cat. That slowed me down wicked.

If a honeycomb cat is tired it should still flow well provided it hasn't lost chunks which you'd hear rattling. Your first slowdown would be at high RPM WOT.

If you do get a new one bear in mind your old one will be worth a lot of money, maybe near $100. Keep it on the shelf if you want to play the commodities market or keep it to swap back in if you start having issues with your aftermarket one. As an aftermarket cat is worth about $15 in scrap-- they have less to them-- it might be worth running just from a POV of if it gets stolen you're out less.

"They" say universal cats flow less and convert less. FWIW. The ones I've fitted seem to flow fine.
 
I appreciate all the responses.
Air filter is checked regularly. Fairly new. I've used a K&N panel in the past but Purolator now. I figured if the air is flowing in, but not flowing out, it has to be the cat with 100k.
I had a cat replaced under warranty with my '01 Sable a few years ago and it was a $900 job at the dealer. Thought Magnaflow and Walker replacements were a good price, name brand and comparable to OEM.
Boost comes on as I try to get it going but the response is unremarkable. I have a $50 code reader, don't know if it would show anything. It tells me the code when any of our cars get a CEL. Never though about the O2 sensors. Interesting.
 
there is a good video from ericthecarguy that gives advice on how to diagnose a bad cat. otherwise its just a guessing game with you spending alot of money and wasting time.
 
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As long as the engine wasn't misfiring or running pretty rich, 100k isn't that long on a catalyst. I've never had one fail under 200k miles... but YMMV, of course.
 
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