Questions for peeps who have replaced their cat converters
 

So I've got a 96 Maxima with 200k miles and a smelly backside :p

I smogged it recently here in Cali, and the NO levels came out very high. And yes, I did drive it around for a good 20-30 minutes before I brought it in. Results were:
At 15 MPH: 1142 PPM NO (the max limit needed to pass was 430 PPM)
At 25 MPH: 1080 PPM NO (the max limit needed to pass was 717 PPM)

Plus my hydrocarbons were just a tad bit high. Results were:
At 15 MPH: 61 PPM HC (the max limit needed to pass was 54 PPM)
At 25 MPH: 20 PPM HC (passed this one, max limit was 37 PPM)

With these results and a pretty terrible smell coming from my tailpipe, I'm guessing the culprit is the cat converter and I should be able to pass emissions if I just replace it. Would you agree? Any alternate opinions or similar experiences with different or additional diagnosis/results? EGR valve maybe? Fuel filter? O2 sensors? All of the above????

Also, should I be seriously considering this: "When replacing your catalytic converter it is often necessary to replace one or more of the oxygen sensors to correct fuel mixture problems. The incorrect fuel mixture will significantly reduce both your gas mileage and the life of the catalytic converter." Quoted from 'calconverter' ebay seller. Should I worry much about replacing my O2 sensors while replacing the cat? If so, which ones?

And this may be an amateur question, but would reusing the old gaskets and bolts on the new cat be frowned upon? Should I get new ones along with the new cat? I guess they're only a few bucks, huh?

There's my first and foremost inquiries. Read on if you dare... ;)

Now since Cali laws are such a pain in the A and I'm a stubborn M/F, I have been reluctant on going with what seems to be the cheapest legal way to replace the cat here in Cali, which would be to have a mechanic weld on an aftermarket universal fit Cali-approved cat for me at a total cost of around $250-$300.

First off, I know my Max, which btw is not a Cali VIN (it came from Maryland), can pass Cali emissions with a much cheaper Fed-spec cat converter...it passed in Cali 4 years ago when I was first registering it here, and again 2 years ago...both times were with a Fed-spec cat. From what I recall, it was the original OEM cat, don't believe it was aftermarket - either way, it wasn't Cali-spec and it passed, also due in part to the very nice smog tester guy not really giving a crap about the visual inspection :D. But of course it is illegal to buy a Fed-spec converter here in Cali or even have one shipped to you from anywhere. I hear it's something like a $10k fine if they catch you. :eek:

Secondly, I'd rather do a direct-fit bolt-on cat to maintain that flexibility of interchanging Y-pipe, cat, B-pipe and tailpipe each individually with the simple removal and installation of bolts, something I can do myself. Having a welder weld a new cat between my Y-pipe (btw it's a Budget Y-pipe, another thing I get away with by going to this smog tester :D) and my B-pipe pretty much eliminates that flexibility. Plus, what if it ends up not being the cat that's the problem and my car still doesn't pass emissions? But of course a bolt-on Cali-approved cat converter runs you at least $340 (DEC) up to the $400's (Magnaflow) and I won't even mention what the OEM cat costs. Whereas the aftermarket Fed-approved bolt-on cat converters that I CAN'T get here in Cali are wayyyyy cheaper.

I am tempted to drive to Arizona and back just to get a cheaper Fed-spec cat to put on myself but factoring in the gas, I wouldn't really be saving much money, if at all, by doing that lol. There's also Tijuana, Mexico only 20 minutes away but I definitely wouldn't know the first place to look over there for a Fed-spec bolt-on cat. Would junkyards be a possibility? I doubt it, but thought I'd throw that out there.

Just thought of another question. This one's quick. Does anyone know if Cali-spec cats would decrease the car's performance/HP at all compared to Fed-spec? Since I assume Cali-spec cats are a little more restrictive in order to clean the exhaust better. Or could this be the reason why they are so much more expensive...they clean the exhaust better without restricting power/performance/mileage any more than a Fed-spec? If this is the case I might as well go with a Cali-spec :D

http://www.google.com/search?client=...w=1440&bih=716

Then a muffler shop can weld it up for about $50. high flow cats are the best you can hope for performance-wise.

This is the same issue that I ran into at my last smog check. I replace my oem cat with a universal one and the NOX reading was higher. I really regret replacing the cat as I went cheap and had the exhaust guy cut off the flanges off the ypipe and my greddy exhaust and had them weld it. I also cleaned the egr tube and confirmed the egr valve works too. I was finally able to pass after running seafoam through the engine and the gas tank. I plan to run seafoam again for this year and hopefully I pass. Good luck.

When I lived in WA, I had a short in the data wire for the obd2 so I always had to take the sniffer test. I would go along with a cat that can be swapped out. If you order a cat there is no way they know what it is coming from another state. When you go to emissions, if you haven't changed spark plugs in awhile, change them, also don't go with dirty oil, go with a fresh change (nothing crazy, just nothing over 2k miles old), also a clean air filter. All these things not done add up. But I would definitely change the cat, it sounds shot.

The only things that can cause high NoX reading are running lean because of a bad o2 sensor or faulty injectors, timing is off, blocked EGR, carbon build-up, or simply running hot because of a faulty component in the cooling system. Likely you have carbon build-up which can be helped by seafoam. I dont think you are running lean but your o2 sensors could be bad as well as your coolant temp sensor which can cause the same fuel ratio issues. Have you ever cleaned you EGR valve? It is probably clogged to some degree. Do some maintenance and see where you are at. I personally dont like sea-foam because it can throw a CEL and simply release carbon only to get caked on your o2 sensors but in small doses when used properly it can help if this is causing you to have high NoX readings. Changing your coolant temperature sensor, if it is still facotry, can only improve your engine performance anyways so its is really up to your where you start but if your cat is also factory then it is likely operating less than efficiently

Before you go out and spend the money on a brand new cat, remove the one you have from your car, clean it out, and then put it back on your car and sees if it filters the exhaust properly, I've done this twice before and it worked both times for me. Personally I filled a bucket with laundry detergent put the car in and let it soak overnight to clean all the crap out, but I have heard of people using parts cleaner to clean them out as well. Its a helluva lot better then going out and spending a couple hundred dollars on a new cat.

Great, helpful info so far guys, thanks!

I figure I am going to regret doing a weld-on cat no matter what. I actually just found a DEC bolt-on Cali-approved cat for only $296 on Ebay: http://www.ebay.com/itm/140679826245...=p5197.c0.m619. So that looks like my cheapest legal option for bolt-on. I figure by getting a bolt-on, I can put it right on myself, go straight to the smog test to see if it passes, and if it doesn't, I'll take it straight to this exhaust guru I know who can hook it up to their fancy shmancy diagnostic system and test everything in the exhaust for around $75 and find the exact problem, all the while knowing that I can still return the new cat if the old cat ends up being fine. Doing it the other way around and going to my exhaust guru first for $75 just makes me think...well what if he finds out it was just my cat? Then I just wasted 75 bucks! lol

Iilac, what's this seafoam method you talk about? Pardon my ignorance, I've never heard of it.

Maxgtr2000, I keep reading on every seller's website that they cannot ship Fed-spec cats to Cali addresses, so I don't think a Fed-spec cat order would even go through if I entered my Cali information. The other option I thought of was to have it shipped to a friend/family member outside of Cali and then have them ship it to me inconspicuously but still I don't know how USPS/UPS/FedEx/DHL handle their inspections and if Cali has special inspections when it comes into this state (wouldn't be surprised). Just still seems not worth the risk of a $10k fine. Thanks for the advice on spark plugs and oil too, those have been on my list. Already took care of the air filter. Fuel filter is on my list too, I figure that might have an effect...but how big of an effect I don't know.

I was writing the message above before I saw a couple more responses from you guys. More helpful info, thanks! Maybe I'll hold off a little longer on getting the cat and try some of the other things you suggest.

I disagree that you should be ruling out your cat. Cats reduce HC, CO, AND NOx. All modern catalytic converters are three way and do an excellent job at reducing these 3 pollutants when at operating temp. A Bad EGR maybe contributing but I personally believe a bad cat could be causing all of your levels to be higher at once.

If your car isn't tuned up, then do that first and ensure your timing is good, then I'd be looking at both your EGR and cat.

And BTW, with a Fed Spec car, the law is on your side. You only need a Fed Spec Cat. Technically by law, all cats installed after 2009 have to be equipped with a CARB NO. and be California certified for CA cars. Honestly tho, how are they going to go about proving you installed a fed spec cat after 2009. Just be aware of the law and confident in your statements, and they are less likely to question you. The key is finding out if there is a number on your current catalytic converter and if they are recording it. If not, and if you end up getting another one, try to find a similar one without identifying marks. I don't know much about the catalytic converter identification, but that would be great if standards weren't implemented on this until 2009.

Good point ct27gt. I was going to mention that I figure a new cat converter is the main component that will reduce all my emissions levels enough to pass smog no matter what other problems exist, if any. Especially if I get a Cali-approved cat. I just need to get this done as soon as possible because I'm risking driving around my car with expired registration every day. Not good, I know.

So would you guys agree when I say that if I just get that brand new bolt-on Cali-approved cat on ebay for $296, install it and bring it back to get smogged, that it'll most likely pass? I figure if I go this route and it passes, I'll be able to re-register it, get that damn 'obey-every-traffic-law-and-watch-out-for-cops-behind-you' mentality off my back, and then go from there as far as figuring out if anything else is wrong with my EGR valve, O2 sensors, etc etc.

Also ct27gt, I understand what you're saying about the Fed-spec cat and that makes sense. I'm confident with a Fed-spec cat my car would pass emissions and not be flagged mainly because of my smog shop's relaxed nature of the visual inspection. The problem is, how do I get a new Fed-spec cat here in Cali without having to jump through hoops? Don't really want to spend the gas money to drive out to Arizona, don't really want to risk getting mugged in Tijuana or getting caught with the cat trying to bring it back across the border, don't think there's any shop or website out there that will send a Fed-spec cat to my Cali address, don't know the risk involved in having a friend/family member outside Cali send one to me, I just don't know. What I'm mainly looking for is anyone who has proved otherwise and knows a fail-proof way of easily getting a Fed-spec cat in Cali (without it already being on your car).

$296? did you not see the link I posted? Most cats use the exact same brick so get the cheapest cali approved cat you can and yes you will have to weld it up but its not a hassle really.

What I would do is run some seafoam through your throttle body CAREFULLY AND IN SMALL DOSES and see where you stand. You cant just go back and test agin to see where you are at but after you do a seafoam treatment and put a new cat on there I would be highly surprised if you NoX numbers dont come down. I am fairly certain they are high because you have some serious carbon buildup, your EGR is partially clogged, and your cat isn't catalyzing efficiently if at all

Welp, looks like I may be able to get a cheap Fed-spec cat pretty easily after all! The seller of this item on ebay is in Canada and says they have shipped Fed-spec converters to Cali before without any problems. Looks like a very trustworthy company that makes quality stuff at low prices, based on the tons of feedback and their website. $109 is a great price for what looks like a well-made direct-fit product. Would you agree? Anybody had experience with this distributor? They say their converter cores come from AirTek. Any other cat manufacturers you think I should look into? I hear Catco is the second to none...

Seafoam is a cleaner with mixed opinions on this forum. It is a engine cleaner that can be purchased at your local automotive store. You can run the cleaner thru the intake to remove carbon deposits. You can use search on youtube or on the org to to get a better feel for it. In my case, after only running the seaform did it lowered the nox to pass smog. Previous smogs after replacing my cat with a catco didnt do anything to lower smog readings for me.

Ok thanks. I'm also reading up on how to take out and clean the EGR tube. Might try that simultaneously with the cat replacement.

And btw Iilac, if you remember, were your NOx readings really really high at first like mine or were they substantially lower than my readings?

I don't remember the actual numbers but I failed the nox reading at 15 mph and barely passed the 25. After replacing cat, cleaning egr, I failed nox at 15 and 25. After using seafoam, I passed nox but my hc readings went higher but good enough to pass. Hopefully this year, I have it registered at a city which will only do sniffer test but not on the dyno.

I would take a peak under your car and just confirm that there is no way for them to identify your current catalytic converter (ie: easily indentifiable numbers, model numbers, etc.). If they somehow have your current catalytic converter on record, then they would have evidence that you have changed it since 2009 if you put in a new one and force you to get a proper catalytic converter. I would say that is your biggest obstacle.

However, make sure your car is in good running condition before even considering replacing the cat.

You have a 96, there is no Cali spec Fed spec emissions. They are all the same.

I know, I realize they didn't start making Cali spec Maximas til 99 or something like that, but that doesn't change the fact that today, most to all manufacturers/distributors will not sell you a Fed spec cat converter in Cali, so even if you have a Fed spec car but its registered in Cali, your only LEGAL choice if you need to replace your cat converter is to buy a Cali spec one. Think I got pretty lucky tho finding this cat distributor in Canada who has no problem with sending Fed spec cats to Cali and at an unbeatable price :D

ct27gt, great advice, thanks.

Also I got a CEL today, hopefully that will shed some light on the emissions issue, I'll have updates soon. Thanks everyone so far for the help.

Btw, there isn't a specific CEL code for the cat converter itself on our 4th gen maximas right? Or is there?

It would throw a code for the 3rd o2 sensor after the cat.

Alright my CEL was evaporative emissions control system. I don't think that has anything to do with exhaust smog levels, right?

Right - the EVAP system captures gas fumes from the fuel tank in a carbon cannister, then pulls them into the engine to burn. Bunch of vacuum lines and valves between the engine and the fuel tank. Which CEL code was it??

I want to say P0450 but as I was looking for a pen to write it down, my damn friend who had the scanner deleted it lol. I know when I initially glanced at it, it was the evap emissions, so I know that for sure. But I didn't glance close enough at the code before I turned my head to look for a pen and my friend deleted it :mad: So I'll have to wait until the CEL comes back on again. At least I know the CEL has nothing to do with my exhaust emissions tho.

This weekend, weather & time permitting, I plan to take off my EGR valve and tube to see if it has some carbon buildup that needs cleaning.

The cat isn't your issue. The engine isn't running right, a/f is off.
Troubleshoot it first, throwing parts at it isn't the way to fix it.
If you can get a scanner and look at live data, you'll probable see fuel trims are off. It may also show some other sensors information that might be questionable.

Clean the throttle body, check the egr tube, put new plugs and an air filter in. If that doesn't clean it up, replace the o2's. Cats don't just stop working, they usually plug up or rust apart.

P0459 translates to the EVAP Control System Pressure Sensor. IT is not used for to directly control the engine systems, but only for on-board diagnosis. For my 1997, this unit mounts on the bracket just in front of the cannister behind the left rear wheel. As I remember, access is pretty easy if you jack up the car and remove the wheel. Looks like it has one vacuum line and a plug with 3 wires (red, white and black). Instructions for testing, locating, etc are in the "EC" section of the FSM. Good luck.

P0459 translates to the EVAP Control System Pressure Sensor. It is not used to directly control the engine systems, but only for on-board diagnosis. For my 1997, this unit mounts on the bracket just in front of the cannister behind the left rear wheel. As I remember, access is pretty easy if you jack up the car and remove the wheel. Looks like it has one vacuum line and a plug with 3 wires (red, white and black). Instructions for testing, locating, etc are in the "EC" section of the FSM. Good luck.

Alright guys so I've made a little progress on the high NOx investigation, but I don't think I've solved the problem yet. I replaced my fuel filter earlier this week, which was VERY clogged. I also removed my EGR tube and Idle Air Control Valve and cleaned those up. The EGR tube had a decent amount of crud in it, but I don't think enough to be the main culprit for high NOx. It wasn't fully blocked by any means, but definitely took a while to give it a good thorough scraping and cleaning.

Timm80, I am going to try your suggestion of removing the cat, placing it in a bucket of detergent water and letting it sit overnight. Hopefully that will help with getting the HC an NOx levels down. I'll take it straight to the smog place after putting the cleaned cat back on and see where I'm at.

If I still don't pass smog, I think my next step will be to troubleshoot the EGR valve. While working on the EGR tube I found out that I might have an issue with the EGR valve, but I'm not totally sure. See this new thread I posted with this issue and a couple others and if you have any comments, post away! :) http://forums.maxima.org/4th-generat...ml#post8719747

I second njmaxseltd's advice. The OEM catalytic converters are very good, aftermarket units are NOT. Don't jump to the conclusion that your OEM cat is bad before ruling out the items he listed.

And EGR is intended to reduce NOx emissions. EGR tube blockage is common on the 4th generation Maxima, and should trigger the MIL.