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Hi everyone. I have an '02 G20 that is throwing a p0420. I got a quote from a local shop to replace the exhaust manifold and Cat, but the quote is more than the blue book value of the car. Looking for the manifold online shows that it can be purchased for about $500, still a huge portion of the total value of the car. I was able to find the same part for a Nissan Sentra for a fraction of the cost. Are these parts interchangeable? This is what I found: https://www.am-autoparts.com/products/direct-fit-catalytic-converter/AM-23819164.html

I would hate to part out the car just because it won't smog, but $500 to fix a $1200 car seems a bit much.

I appreciate any help anyone can offer on the interchangeability of the parts.

Bill in Tacoma.
 

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Woah. Second opinion . Use $5 from walmart maf cleaner and clean the mass air flow.( Check your distributor timing. Hold down bolt on top should be close to center twist forward to advance. My exhaust stunk ALOT less when i advanced it to about 20 base on 92 octane.). When was spark plugs last replaced? Check vacuum lines are routed correct.
 

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If those don't work try seafoam in the tank to clean injectors. Also check that spark plug wires are correct on the distributor should be numbers on the cap and far left is cylinder 1 going right then 2 3 4. Good luck with it
 

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Woah. Second opinion . Use $5 from walmart electronics cleaner and clean the mass air flow.( Check your distributor timing. Hold down bolt on top should be close to center twist forward to advance. My exhaust stunk ALOT less when i advanced it to about 25 base on 92 octane.). When was spark plugs last replaced? Check vacuum lines are routed correct. use that electronic cleaner and spray around the intake and vacuum connections, if idle changes there is a leak. I am 99% it's not what they quoted you for bub.
I just replaced the spark plugs and the code came back. I'll try running some premium in it and check the timing. The MAF failed 3 years ago, and was replaced but I'll clean the MAF sensor and see if that helps. I'll also test the hoses for leaks like you suggested too. Hopefully one of those will get me enough to keep that light off long enough to pass emissions. I'll keep you posted.
 

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If you have timing gun set it to about 15. Not 25 that was an example. I go nuts on timing and in Florida no emissions. Do you know how to test 02 sensors? Maybe just unplug and reconnect.
 

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That converter is for the 2.5L engine and will not fit. Definitely you need to replace the converter. Find someone who is parting out their car and buy it. I was lucky that a local member sold me a used one for $40. Another option is the junk yard.
 

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I would get the whole exhaust off a 99' G20 and replace the cat with a aftermarket one. The 00+ manifold/cats are getting hard to find with low mileage, and being integrated into the exhaust manifold they are disposable. I may have a mani/cat off my 132k 02' auto if you are interested.
 

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Whew just had to login to reply to this! I had the same code. I was super worried about a problem with the Cat because of how expensive it can be.. I have a friend that is a mechanic and recommended use CATACLEAN first to see if it cleared the code up. I had doubts that an additive would help, but I trust him and tried it. It cleared the code up. I realize I might sound like an ad, but this product actually worked for me. It was worth a shot for me since it's only $30 and trying any other solution would cost twice that easily.
I got mine at Autozone

http://www.autobarn.net/cataclean.html?site=google_base&gclid=CNOPm_zamNMCFcSIswod9ZoDpw
 

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Did you solve this issue? I have the same problem. Shop told me it was throwing a code for the CAT... Never saw it with my own eyes and they didn't give me the code. I'm wondering now if it is the oxygen sensors or a leak. I bought a crx because to daily but still have my G sitting outside for 6 months now because I can't register it. CA is especially a pain in the ass.
 

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I had the same thing happen on my girls Scion TC that I just rebuilt. The cat has so many miles (159k miles) that it doesn't do it's job anymore and needs to be replaced. It's a very common problem after 145k miles or so on most cars. Fortunately our city/state doesn't require us to fix it to pass. I'll probably weld in an aftermarket cat downstream and move the rear o2 behind it since the manifold/cat is pretty expensive.

For the 00 up G20 and sentra 2.0 SE it's pretty easy to convert over to the old style cat converter that is under the car and not built into the manifold. Just need the 99' G20 manifold and pipework.
 

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I have a 02 G20 and getting the P0420. How do you convert over to the old style cat under the car? There is a cat under the car already, do I just move the rear o2 behind that car? To replace the mani cat, do I install a header?
 

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Just get the full exhaust off of a 99' (manifold to muffler) extend the secondary O2 wires so they reach the cat under the car. (make sure you extend the car harness wires and not the O2 wires since they are high temp and can not be soldered) The 00'-up have the main cat converter built into the manifold and a second "finisher or half cat" under the car. The 99' only has 1 big cat under the car with a bung on the rear for the 2nd O2. The 1st O2 goes into the exhaust manifold on both styles so there is no modification needed.
 

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I heard soaking the parts in some hard cleaners would help with that. ETCG on youtube soaked his cat in various cleaners to see if theyd clean it up and make it reuseable, but honestly id just go with a universal cat. Its like 100$ at vatozone, so its not terrible. For the manifold, try the same thing. Soak it in like a deep cleaner and see all the grime that comes out of it. Inspect the tubes and the welds to make sure the manifold isnt cracked, cuz even small cracks are a big deal. Imo this is a prime opportunity to get an aftermarket manifold for better exhaust flow, if youre into performance or a small gain in fuel economy.

I googled up your code, p0420, and it says "catalyst system efficiency below threshold bank 1". Thats before the cat, so im not sure why hes trying to sell you a cat if the problem exists before it. Id try cleaning both first before you start buying new things.
 

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Usually the material in the catalytic converter starts to degrade and blow out of the tail pipe. If you look inside a 140+k mile converter or weigh it you will understand why. They don't do their job when they are empty. I have had this happen on quite a few cars now.
 

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I've been a mechanic for 27 years now and in all honesty only half of the vehicles that come in with a P0420 code actually need a cat. First things first, if you haven't done so yet start with a complete tune-up with good parts like NGK plugs, wires and replace your distributor cap and rotor - make sure you check the spark plug gap - they do not come pre set and I recommend torquing them to spec. Replace your air filter and do an oil change with a conventional name brand oil and filter. I suggest using 10w30 or 10w40. After that clear the codes and drive it on the highway to get it lit. If you're like me and don't do a lot of highway driving, your car will throw this code but getting it on the highway regularly has kept it off in my 02 P11 sport and I'm the original owner. Something you should look into is your fuel trims warmed up at idle and at 2500 rpm - anything +5% or - 5% would indicate a problem elsewhere and you will keep throwing the code.
 
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