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I purchased a 2002 Nissan Altima 2.5L 4 cylinder and I too have a bad catalytic converter. Alright so this sounds like a common problem for 2002-2003 Nissan Altima’s, but do we know what’s causing this? Could it be bad/Cheap Gas? What can we do to prevent this problem from happening again, and what can I do regularly to maintain a clean Cat Converter?
Ok and for the purchase of a new Cat converter, do you guys recommend buying a new 600$ Cat from the dealer or a used one from a junk yard? Is it possible this new cat from the dealer is an upgraded version for these Altima’s so this problem wouldn’t happen so soon again? If it’s not an updated version I would much rather just purchase a used one for a fraction of the price.
I purchased my Altima at 125,000 Miles. I ran the VIN with a Nissan dealership and it already has had a Catalytic converter change at 60,000 Miles. C’mon Nissan, this shouldn’t be happening every 60,000 Miles! Ok so let me break down my questions for all of you in numerical order,
1. What can we do to prevent this problem from happening again, and what can I do regularly to maintain a clean Cat Converter?
2. Do you guys recommend buying a new 600$ Cat from the dealer or a used one from a junk yard?
3. Is it possible this new cat from the dealer is an upgraded version for these Altima’s so this problem wouldn’t happen so soon again?

And for a fourth off topic question, how often should I replace a timing belt? Yes this is my first Nissan and being only 19, I don’t know much about it. I came from a 1996 Toyota Camry that I loved dearly. I will also include a picture of my new sweetheart, what do you guys think? I got it the way you see it, haven’t done anything to it personally besides regular tune up work. Thanks for reading, tried my best to write it clearly as I could. :)
 

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XxJESTERSxX
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If you don't live in California I would get 2 things

1.Headers
2.Full custom exhaust

And then you would have NO cats and a faster car!!
 

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2488cc
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Are you saying the pre-cat in the header went bad, or the main-cat along the underbody of your car? The pre-cat is the main failure for our car, and I would just recommend a straight through header off of eBay (~$100) rather than buying another cat.
 

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My therory is the top bung on the primary O2 sensor was fuse welded in place, via some induction method. The heat cycles, bad fitment and or replacing the O2 sensor cause a leak or crack. This lets extra air in the system boosting the surface temp on the substrate right by the bung. This dust then gets sucked back into the motor due the overlap on the cams. eating the o-rings and head gasket.

Now you have think at 3000rpm the internal temp of the gasses is around 800 to 1000 degrease. Higher if you are running it harder. With the presence of added O2 unburnt fuel and or the oxidizing effect of oxygen causes the substrate to turn to dust. This dust is silica, iridium, platimum, and few other rare earth metals. All of which are harder than the Nicolite/Iron sleeve in the block. can you say sandpaper.

When replacing head gasket I took my precat off and smashed it out. It seams to work good. with a 2" spacer I fab'ed for the Bottom O2 Sensor.
O' I welded the leaking top bung. Now no more exhaust leak.

GET RID OF THE PRECAT. It is eating your motor as we speak. If you car is under 80k miles have Nissan REPLACE THE MOTOR FREE OF CHARGE! GET THE HEADER.
 

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Welcome to the Nissan fam. Sorry for the loss of the camry. My mom had a 96 Camry really good car. Anyway At least your on the ball with trying to figure out the cat issue. I didn't find out till my engine was shot. To help bring some clearity for you. We have 2 Cats'. 1) is right in the front. It comes as one piece with your header right underneath the heat shield (if yours is still on). 2) is underneath the vehichle almost midway down your exhaust system. Now I don't where you live at or if you care about emissions, but in FL we don't have emissions laws or anything, so I had the #2cat cut off and had a straight pipe ran, and of course a straight header in the front to replace the #1 cat, but that's the route you probably want to go. As far a replacing your timing chain (As I said earlier welcome to the Nissan fam) Unlike other makes Honda, Toyota, etc.. you hopefully shouldn't have to ever replace that, unless you are just beatin the heck out of your car. I hope that helps, and have fun
 

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The timing chain is rated for a longer running interval than the head. So he's right, no worries. If you hear a wirrrrrrrrr sound when you start the engine that is the chain tensor coming into tightness. If you are low on oil it takes about 2 seconds longer for the oil pressure to come up. The tensioner applies pressure to the chain via pressurized oil. (there is a spring involved but it does little work)

Wiiiiiirrrr = low oil.
Constant low oil = burning oil = failed precat = bad motor.

o
 

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QR25DE Pre-cat?

If the Pre-cat , that is known Problem and has ruined too many engines..

Aftermarket Header is your answer. No pre-cat on manifold = no problems!!

Let me know if I can help!

Good luck,

Mark

If your main cat mid car, any muffler shop can flange/weld in a new one for
$1XX-$2XX no problem.
 

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Discussion Starter #8
Ok yall, im back after a long day at the shop with this nissan and im here to report my very bad news..... :( so after taking the precat off and the cat underneath the car we noticed the mesh stuff inside the precat has been taken out, someone has messed with this before. tried flushing it with alcohol just for testing reasons. Checked compression and all seems good. but i now just found out i have the Burning oil problem, too late to be fixed now... the engine seems to be driving fine but doesnt have enough power as it should. and theres quite of bit of smoke that comes from the exhaust, and by the way, i live in california so i cant do the straight pipe option. I think im stuck with this faulty engine now :( ahh i dont really have any more options now. The car runs and drives, just burns oil and i wont be able to pass smog, cant pass smog then i cant register. im screwed.
 

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Dang man that sucks! So let me ask you a question. When at the shop did you examin the head gasket to see if it was damaged or not? That could be the issue. Did you check your oil as in is contaminated with something else i.e coolant or fool?
 

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Ok don't freak!

Listen the precat is only there to make sure the vehicle is VLEM (very low emissions vehicle)
Now you have what I have done, I smashed out mine. no biggy, you still have the secondary Cat. Now, what I would do is inspect the secondary and see if it is filled with soot or if you can shine light/see light through it. If all's good, go to the emissions place BEFORE YOU HAVE TO GO and have it tested. Make sure the car is hot and that it doesn't get much of a chance to cool down. See if it passes, if not you will have to replace it, if that is the case the precat will eat all the oil fumes......mine did.....

Aaron
 

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if that is the case the precat will eat all the oil fumes......mine did.....

Aaron
Okay are you sayin that after you punched out the precat it ate all the oil fumes? If so did it still continue to burn oil?
 

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Ok don't freak!

Listen the precat is only there to make sure the vehicle is VLEM (very low emissions vehicle)
Now you have what I have done, I smashed out mine. no biggy, you still have the secondary Cat. Now, what I would do is inspect the secondary and see if it is filled with soot or if you can shine light/see light through it. If all's good, go to the emissions place BEFORE YOU HAVE TO GO and have it tested. Make sure the car is hot and that it doesn't get much of a chance to cool down. See if it passes, if not you will have to replace it, if that is the case the precat will eat all the oil fumes......mine did.....

Aaron

ok sorry let me explain, after we took of the precat we noticed it has been inside has been removed, we removed the other half of the cat that runs along under the car into the precat, and tried cleaning it with alot of alcohal, and also drilled a hole into it, because i have an extra one from my brothers 02 altima. the precat had nothing to clean and we put all this back together, and still have this oil burning problem. so much smoke to if i just rev the car in park. :(
head gasket seems to be fine and i dont see how this can be an overheating issue. maybe i just dont know what im talking about :banghead: we also changed the oil to high mileage oil, wich is a little bit thicker, and added a can of engine restore. i still think i have a bad engine.. idk
 

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ok sorry let me explain, after we took of the precat we noticed it has been inside has been removed, we removed the other half of the cat that runs along under the car into the precat, and tried cleaning it with alot of alcohal, and also drilled a hole into it, because i have an extra one from my brothers 02 altima. the precat had nothing to clean and we put all this back together, and still have this oil burning problem. so much smoke to if i just rev the car in park. :(
head gasket seems to be fine and i dont see how this can be an overheating issue. maybe i just dont know what im talking about :banghead: we also changed the oil to high mileage oil, wich is a little bit thicker, and added a can of engine restore. i still think i have a bad engine.. idk
:sad:Yeah bro hate to be the bearer of bad news, but it doesn't sound to good for the engine. See it's not really the precat that burns the oil. It's the broken fragments from a bad precat that damage the engine. So you need to check the other eningine components for damage. i.e head gasket, valve guides and seals. When it happened to me I tryed thicker oil and additives like lucas, but the problem is bigger than that.
 

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Just putting it out there, but if you have a bad pre-cat, i'll sell you mine for 40 bucks + shipping. It's from an 05 altima 2.5s. You can just bolt that bad boy up and be done and pass your emissions testing.

On the cat being gutted, I just did that today and you can just have a high flow cat welded on or something. No sense in buying a brand OEM one if they're just going to fail.
 

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:sad:Yeah bro hate to be the bearer of bad news, but it doesn't sound to good for the engine. See it's not really the precat that burns the oil. It's the broken fragments from a bad precat that damage the engine. So you need to check the other eningine components for damage. i.e head gasket, valve guides and seals. When it happened to me I tryed thicker oil and additives like lucas, but the problem is bigger than that.
thats funny that you say that cause we were trying the exact same thing, thicker oil and a can of engine restore. ahh so this isnt fixable? or worth fixing?
 

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thats funny that you say that cause we were trying the exact same thing, thicker oil and a can of engine restore. ahh so this isnt fixable? or worth fixing?
I wouldn't say it's not fixable. As far as the worth fixing part. It's all on the individual/budget, and the condition of your engine. I don't know if your still driving it right now, but you need to get a look at that engine again, cause it sounds like it might go pretty soon. Before mine went I was blowing heavy smoke(I mean heavy) even in the park position, and a couple days later the engine locked up with like 4 quarts of oil and a bottle of Lucas chillin in it.
 

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I wouldn't say it's not fixable. As far as the worth fixing part. It's all on the individual/budget, and the condition of your engine. I don't know if your still driving it right now, but you need to get a look at that engine again, cause it sounds like it might go pretty soon. Before mine went I was blowing heavy smoke(I mean heavy) even in the park position, and a couple days later the engine locked up with like 4 quarts of oil and a bottle of Lucas chillin in it.
my smoke isnt to bad, wouldnt really notice it sitting idle at all, but once you hit some gas then all hell breaks loose! ok im being over dramatic but yea its no good for the air definably :banghead:
 

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my smoke isnt to bad, wouldnt really notice it sitting idle at all, but once you hit some gas then all hell breaks loose! ok im being over dramatic but yea its no good for the air definably :banghead:
In that case it doesn't sound like your on the edge of dissaster, but yeah if your wanting to pass emissions test IMO I would try to tackle then engine before I went for the exhaust systems. Not saying that you wouldn't have to fool with the exhaust system, but it wouldn't be my priority.
 

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In that case it doesn't sound like your on the edge of dissaster, but yeah if your wanting to pass emissions test IMO I would try to tackle then engine before I went for the exhaust systems. Not saying that you wouldn't have to fool with the exhaust system, but it wouldn't be my priority.
in this condition how much do you think the car is worth? for a fair sale on craigslist. its 126k miles. pretty clean body and interior.
 

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in this condition how much do you think the car is worth? for a fair sale on craigslist. its 126k miles. pretty clean body and interior.
Not really sure. I don't know if there is a Carmax in your area, but I had a really good experiance with selling a 01 altima to them. The car was in bad shape running wise, and the body/interior was in decent shape with a few scuffs and dings. I think I was knocking on the 100k mi marker, but the gave over 4k and this was in 2006. But to answer your question more directly. I think the majority of people buying on Craigs are looking to get items at a steal of a price. Iv'e Alti's in my area selling for the cheapest about 4,500, and thats assuming that there's nothing wrong with the car.
 
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