VanHowie

Wondering if you guys could share your thoughts/experiences on OEM vs. aftermarket "main" or "rear" cats to help ease my mind. Here's my situation:

Fed spec 96 Max registered in Cali with 214k miles on it. Replaced the original OEM "main/rear" cat with an aftermarket bolt-on Cali-certified cat about a year ago after it failed smog pretty badly. After doing that and fixing up the EGR system, the car passed, not with flying colors, but passed.

Here we are about a year later and I need to renew registration and pass smog AGAIN.

Here is what the status of my car was before I brought it in to the smog check a couple weeks ago: oil was new enough, I used highest octane top tier gas (Chevron) as I always do, the EGR system was re-checked and had no issues, plus no other issues found with spark plugs or O2 sensors or anything like that, I put in a new knock sensor and evap purge control valve (the one mounted above the throttle body) to successfully clear two CEL codes, had no other CEL codes, drove it around plenty, I had used Gumout Regane high mileage fuel injector cleaner a couple times through a quarter of a tank each time, also used a couple bottles of Guaranteed-to-Pass ran through a full tank, and right after I refilled to full I drove it highway and street for 30+ minutes before taking it right to the smog shop for the test and left it running while I was waiting.

After all that the car still failed with high HC and NO at 15 MPH (HC was borderline and NO was double the limit), and at 25 MPH high*ish* HC (not over the limit) but normal-looking NO (407 ppm measured...limit is 717). CO levels seem to always be decent, or at least below the limit.

My car has a Budget Y-pipe on it which of course gets rid of the two pre-cats, but other than that and besides my K&N filter intake, there are no other mods I've done that could affect emissions.

Now what I THINK the "final" problem is is that the aftermarket cat I have is just a piece of crap and didn't last me very long, as I hear aftermarket cats usually underperform OEM by a lot. Perhaps aftermarket cats depend more on the pre-cats and since my car doesn't have any pre-cats the aftermarket cat crapped out on me after 1+ years of use.

After finding out that MaxFever1987 (good seller on here btw) had a used OEM aftermarket cat off a Cali spec 99 Max with 112k miles, which he said had recently passed smog in NY, I was sold and bought that off him in a heartbeat, hoping it will solve my troubles.

So here I am now with his OEM cat bolted on, which ended up being just a bit shorter than my 96, since the 96 fed spec O2 sensor location and other random exhaust stuff differs slightly from a 99 Cali spec. No big deal, I will have a welder weld it in to seal the gaps and put in a new bung for the rear O2 sensor, seems like for a decent price too ($100).

BUT BEFORE I DO THIS, I wanted to see if you guys have any thoughts on my situation. Particularly on your experience with aftermarket vs. OEM cats. My original OEM cat lasted and performed efficiently, as far as I can tell, for about 200k....about 100k of which was with the Budget Y-pipe...so I figure I might have a decent chance with this used OEM cat with 112k to last me just a bit longer (or more) than a crappy aftermarket cat would. Any counter-opinions to that? The welder thinks I am wasting my time with this used cat, and the test-only smog guy, while he agrees that aftermarket cats are mostly pretty crappy compared to OEM, is still hesitant for me with this used OEM cat. I'm hesitant too. Hence why I decided to write this post to see if there's anyone out there that can help ease my mind or instead tell me WAIT STOP, TRY THIS INSTEAD.

njmaxseltd

iTrader: (19)

How do you know that there are no issues with o2's? They might be sending data back to the ECU, but is that information really correct? Honestly, I don't think your aftermarket cat is the issue as long as it was the correct part for your vehicle. I'd be looking at the o2 sensors as the cause, especially if their older.

maxgtr2000

iTrader: (29)

I would try the cat since you did all the other stuff that would prevent the high NO reading. I remember I ended up having to do the smog test in WA state, because I had too many systems not ready after clearing a CEL. I ran ngk coppers and would change them when I had to test. The HC being borderline I always go with fresh plugs, oil, and clean air filter. I had a Walker brand cat installed since it was cheap but it worked with my 2.5" piping. Where your cat mounts I would have a test pipe, and only put the cat on for inspections and such, that way there is no question if it good or not. Oh yeah if your o2s are more than 3 years old change them. They are around $30 each on ebay. If you can get a free diagnotic somehow (or have a scanner that can read o2 voltage) you would see even though o2s don't throw a code, the switching voltage response would be slow enough to cause the high readings.

VanHowie

You guys are pretty much saying what I've been thinking in the back of my head. Those damn O2 sensors. I guess they really could have that much of an affect on controlling what's going on upstream of the exhaust to the point where they could be the root cause of the high readings, huh? I can't remember the last time I replaced my O2 sensors but they haven't 'noticeably' given me any trouble. Either way I think this might be a red flag for me to check into the O2's a little more before I weld on this OEM cat.

VanHowie

....or maybe just do both. Weld on the OEM cat and replace the O2 sensors at the same time. I just still feel iffy about these aftermarket cats.

VanHowie

O2 sensors could potentially have an affect on NO right? If they send the wrong signals to the ECU and then the ECU decides to run the engine rich and then we get more NO, right?

VanHowie

Found this helpful info. This type of stuff might be in the Max FAQs too I didn't check yet (don't hate me! lol) https://answers.yahoo.com/question/i...=1006052655596

dwapenyi

iTrader: (3)

Tired primary O2s huh?

dwapenyi

iTrader: (3)

Definitely replace your primary O2s, especially if you've never replaced them before. They get tired and wont throw a check engine light. Since the primary O2 are responsible for determining air/fuel mixture, when they get tired they give dirty readings to the ECU. Not enough to turn on the CEL, though.

You've taken care of the EGR and brand new aftermarket CAT. They should work. And the difference between and aftermarket CAT and OEM is length of time. OEM will last waaaaay longer. Brand new both should be just as effective at cleaning the car's exhaust.

That Yahoo link is funny. Jules G, who has the best answer, says that O2s dont affect HC emissions. He then goes on to say that bad HC emissions are caused by incomplete burn of fuel, which could be caused by misfire and incorrect fuel mixture. Then, he goes further to acknowledge that the O2s play a role in adjusting air/fuel mixture. I'm like WTF?

I do think that Jules G really does know what he's talking about, I just disagree with him on the O2 part.

Also, to clean up your fuel system, have you done FPR and fuel filter? Fuel filter is an every 30K miles maintenance item. If you've never done it, it is waaaay overdue. The FPR is an item that has no maintenance schedule. But it is also a moving part that gets tired over time. Replace it. You'll see.

Lastly, I would add TCW3 to the mix;

https://maxima.org/forums/fluids-lub...itive-new.html

All these fuel related items will bring your injectors back to optimum performance, so when the ECU tells them to fire for so many milliseconds, they act just as good as when they were new. This will go a long way towards cleaning up your emissions. TCW3 will lube the injectors and clean up all the carbon in the intake system.

Maybe you'll need to take a blast on the highway, too. After doing the FPR, fuel filter, and TCW3 etc, the higher exhaust velocities will help to shove all the dirt and gunk out of the exhaust.

Hope this helps.

VanHowie

Forgot to mention that I replaced the fuel filter about a year ago, so I'm good on that. I believe I replaced all the spark plugs at that time too. Have to go back and look at my records/receipts. Don't know what FPR is so I'll look into that and the TCW3.

VanHowie

The only thing tho with the O2 sensors is I would think that my smog guru mechanic, who I brought it to for an initial pre-test and full diagnosis before doing all this other stuff and bringing it in for the real test, would have noticed if the O2 sensors were faulty and told me to replace them. From what I recall he didn't mention the O2 sensors at all so I'm going to call him today and if he can't give me a definitive answer that he checked those guys during his diagnosis I think I'll just replace the damn things. Found em for $22 on ebay. The NTK's. And I hear the downstream one doesn't affect air/fuel mixture so I won't mess with that one, just the two upstream.

dwapenyi

iTrader: (3)

Exactly, the primary O2s

FPR = Fuel pressure regulator. You passed right by it when you replaced the knock sensor. It's that little flying saucer shaped thing at the beginning of the fuel rail. Follow the fuel line from the fuel filter, up past and behind the throttle body, into the fuel rail. You need to remove the airbox MAF etc to work on it. May as replace the PCV too since its right next to it.

CS_AR

I did a search on TC-W3 and Wal*Mart seems to be get the most results.

Is this the TC-W3 product?

http://www.walmart.com/ip/Super-Tech...fl-oz/16913695

dwapenyi

iTrader: (3)

Holy Smokes Batman! Maxima.org has gone into the twilight zone!

Did anybody else notice how this thread was listing backwards for a brief moment? The OP was listed last and my last post was listed 1st. Bizarre.

Then it corrected itself. So, I'm the crazy one

dwapenyi

iTrader: (3)

Yeah thats it. Walmart SuperTech oil. You can get it in gallon containers too.

njmaxseltd

iTrader: (19)

His diagnostics was to check for any stored or pending trouble codes, so he couldn't have seen a working, but inaccurate O2 sensor.

Leave the Cat alone, replace the O2's. You'll probably see an increase in MPG too.

CS_AR

For my OBD1 car I replace the O2s at 60,000 miles and for the OBD2 cars I usually replace shortly after 100,000 miles. I treat them like spark plugs as a maintenance item.

Side note -- I'll give TC-W3 a try.. Most of the noise coming from MaxII these days is from the injectors..

VanHowie

For the TCW3...I've got between 3/4 and a full tank right now with a bottle of Gumout Regane high mileage fuel injector cleaner already in there (put it in when tank was empty and then filled it to full). My question is should I wait until an empty tank to put in the TCW3 and refill to full? 1oz per 4-5 gallons, right? Or would it matter if I put it in now?

Fakie J Farkerton

iTrader: (51)

https://maxima.org/forums/fluids-lub...itive-new.html

PH98I30

Every time I had a high NOX problem, it was either the EGR was clogged up or the O2 sensors were going bad... even though I never had any codes. My guess would be lazy or old O2 sensors. They are a relatively inexpensive fix. You probably could use new ones anyway.

VanHowie

So I've got a pair of NTK 24018's on their way to me for cheap (http://www.ebay.com/itm/BULK-NEW-NTK...7dbb7e&vxp=mtr) but I'm nervous now if they will actually fit my two upstreams or not. See my posts on this thread for why: https://maxima.org/forums/4th-genera...irt-cheap.html

VanHowie

Anyways if anyone thinks I should be getting the NTK 24525's instead of the 24018's for the two upstreams on my '96 Max' that was MADE on 11/95, let me know.

dwapenyi

iTrader: (3)

Watch. After like 2 tankfuls, your car will purr like a kitten.

It will idle so smoothly afterwards that you just might start the car even when it's still running.

dwapenyi

iTrader: (3)

IMO the beauty about TCW3 is that it is just a motor oil, not a chemical additive like other cleaners. You can add it now or later.

CS_AR

Somebody should buy it in bulk then put it in a fancy bottle and sell for $10 a pint it as a fuel additive named Blue Velvet.

Blue Velvet makes your engine run velvety smooth.

VanHowie

Can't wait to get me some TCW3 :P Although IMO my car already seems to be smoother than I'd expect at idle for a 214k car and not too too noisy or anything like that, even with the Budget Y-pipe and K&N cone intake. It'll be interesting to see if my perspective on that changes once I go through a couple tanks with TCW3

And I suppose it doesn't matter if I put the TCW3 in first and then fill the tank, or vice versa, does it? Maybe if I put the TCW3 in first it'll get to the fuel injectors faster than if I put it in after a full tank.

Also btw I called NGK tech support and they confirmed that 24018 and 24525 are the same part. The 24525 # replaced the 24018 # at some point just for cataloguing purposes. Phew.

CMax03

iTrader: (3)

I've run Magnaflow/Warpspeed cats both Metallic subs and ceramic subs with no issue for over 10 yrs both with headers, catbacks, and 1 with cams....Passed with half the amount of emitted allowed and had 300,000 miles on these vehicle. I personally think where you screwed up was taking your Max to them with that cleaner still in your gas tank and using the same oil you had during the cleaning process. I found that changing my oil and filter b4 the emission test cleaned up the emission immensely on my 86.5 Z24i powered D21 w/headers, Hi flo cat (Magnaflow),catback, Cam and again 300K miles plus....but you must at least know if your O2 sensors are working correctly and if their are suppect then change them with quality units and relax your mind knowing you'll be a winner at the emission test! I did this testing for over 10 ten years on my D21 and never failed!

CS_AR

Today I added 4 ounces to 18.5 gallons (a full tank) of Shell 93 octane. That is 1 oz to 4.625 gallons to start. Next time I will add 2 oz to 10 gallons of fuel.

Soon afterward I could tell the engine is running a little smoother and seems to have a little more low end torque. So far so good. I hope it helps keep the EGR pipe a bit cleaner.

dwapenyi

iTrader: (3)

You should notice your exhaust pipe getting black from all the carbon getting cleaned out. My butt dyno also noticed an increase in low end too, but I had t ask myself, was it an increase or was the car developing more or less the same power, just doing it quietly?

Either way, TCW3 is awesome.

PH98I30

OK, you guys are almost always right on here in suggesting things, so I thought I would try some TCW3. I didn't expect much. When the car seemed to run smoother I thought it might be a psychological thing. Then my GF got in the car and was surprised we were moving because she thought the engine was off. She honestly couldn't hear the engine running. It has been in the gas for 3 days and it has smoothed out the idle & feels like a power increase.... also, I guess we all got a little off topic here with the cat, y-pipe thing?

VanHowie

Alright guys I got an update on my situation here. There's light at the end of the tunnel.

I replaced my (not sure how old, but def not original) Bosch O2 sensors with new NTK O2 sensors (the two upstream primary - found em on ebay for $22 a piece, hopefully they're legit) and that did not seem to solve anything. I took it for a PRE-test (where they just test it and don't send the info to DMV - found a guy who would do it for $10 - awesome) a day after putting on the new sensors (with the year-old aftermarket cat still on there) and the NO and HC levels actually were worse than they were before - after driving it around for 20-30 min to warm it up.

So today I finally decided to test my luck with the used OEM cat instead of saying eff it and putting on a brand new aftermarket cat. Took it to my welder and he put on the OEM cat plus replaced the downstream O2 sensor which I had also bought an NTK replacement for, just for the hell of it - it was cheap.

After that I took it for a good hour and a half drive before taking it back in for another pre-test. This time the emissions levels were initially the same as before. But after the mechanic decided to give it a second try a few moments after the first, we found out that the NO levels were dramatically lowered, and the HC levels became bearable.

So I took that as a very good sign and ran with it. At least I knew now the OEM cat was doing something right. After a couple hours I took it to my original smog guy who had done the original "official" test that failed (since I had one free RE-test with him - meaning if I passed the re-test, the info would automatically go to DMV and my troubles would be over). He was about 20 minutes away so it was a good drive to warm up the car enough to have some confidence. To further my confidence, when I got there, while I was waiting, I sat in the car and rev'd the engine between 2k and 3k rpm until they told me to pull it in to the garage. The car sat at idle for a couple minutes before the test, which made me nervous, but I noticed the guy rev'd the engine for me right before running the test. YES...he got the hint. Awesome guy

The results...after allllllll this....... Still a fail BUT...ONLY with high HC levels now. The NO levels remained tamed. At 15 MPH the NO levels were 376 (limit being 430) and at 25 MPH the NO levels were an amazing 123 (limit being 717). But at 15 MPH the HC levels were 95 (limit being 54) and at 25 MPH they were right at the limit of 37. In other words....I WAS SO FREAKIN CLOSE! lol

VanHowie

So to add to my post above, it seems now my issue is basically that I have high HC. The smog guy and I agreed that the used OEM cat is still in good shape. Gotta love OEM

One other thing to note, but probably doesn't make much of a difference, is that when I took it in today for the pre-test and the re-test, the tank full of 91 octane Chevron w/ Techron gas that I had added Gumout Regane High Mileage Cleaner to a couple weeks ago was just about empty, meaning pretty much all the Gumout had gone through the system and I had no more additives in the fuel. I refilled right before the re-test with just a gallon of Shell 91 octane.

What I haven't done yet is the TC-W3 and the fuel pressure regulator replacement. I am now also considering SeaFoam...in either the air intake, or the fuel tank, or both? Curious if anyone has any advice on that. Also curious if anyone has anything to say specifically about TC-W3 helping to lower their HC levels in particular. Any further thoughts/suggestions/ideas/opinions would be greatly appreciated Thanks y'all.

VanHowie

Oh. I guess I should have went back to the TC-W3 link first and frickin re-read the first post that specifically says "*reduced hydrocarbon emissions" lol!

Ok so what's everyone's thoughts on how long I should wait for TC-W3 to work its magic before I take it back in for a smog test? Full tank? Should I try a quarter tank with an ounce of TC-W3 and see what that does?

Also...the reason I mentioned SeaFoam is because 1. the smog guy suggested it and 2. I realized I already have a full bottle of it that I bought like a year ago thinking I would try it out then never did...I think because I heard some horror stories or something...

Fakie J Farkerton

iTrader: (51)

TCW3 takes about 3 tank fills to really shine.

PH98I30

Try getting your smog done first thing in the morning. In 8 smog tests between my car & my girlfriends car, 5 tests were done first thing in the morning. In all 5 cases, the cars passed with low emissions. In the 3 other cases the test was done in the afternoon. One passed with high readings and 2 failed the test. Maybe the afternoon tests alter the readings of the equipment or the equipment is contaminated from all the other tests. It might be worth a try.

dwapenyi

iTrader: (3)

Seafoam and TC-W3 do the same thing, but TC-W3 is more gentle. It's just a motor oil. Seafoam contains alcohol, so it has the potential to do more harm than good. With TC-W3 there is absolutely no concern for any potential harm.

VanHowie

Oh my god I'm dumb I should have taken the time to look at my mechanic receipts a long time ago. I gotta stop neglecting my freakin glove box. Turns out I THOUGHT I had a mechanic replace my spark plugs last year. Looks like I DIDN'T end up having that done. Only the fuel filter. Last receipt I could find with changed spark plugs on it was about 60,000 miles ago. Yup. Time to change em! When I looked deep in my glove box and found six brand new genuine OEM spark plugs in their boxes that I had bought from the dealership a year ago, I was just like....DOH!! Will replace those tonight, hopefully that will be enough to lower the HC levels to pass.

CMax03

iTrader: (3)

Just change your oil b4 you do your test and you'll be ok! You keep adding cleaners and more cleaners in your tank and they're causing you to fail....change your oil and go test and you will pass!

CMax03

iTrader: (3)

My truck has headers, a performance cam, ignition, custom exhaust, and 350K miles and passed with flying colors for over 10 years doing this same thing b4 an emissions test...."Just Do It"

VanHowie

Put in new spark plugs and PASSED! FINALLY. The old spark plugs were pretty corroded, so I figure putting in the new ones helped lower my HC enough to pass. Plus my smog guy was again awesome enough to rev the engine for me right before hooking it up to the tester, which seems to REALLY help out.

FYI to CMax03, I didn't feel a need to change the oil...it is synthetic with 2500 miles on it so I figured it wouldn't make a huge difference if I changed it. FYI to PH98I30, I did take it to the smog place in the morning this time, not to say that I actually believe doing a morning test is advantageous over an afternoon test, but hey it passed so ya never know :P

The HC levels were still kinda close to the limit so yesterday I put in a fresh full tank of gas with 4 oz. of TC-W3...which I figure will only help the HC situation with less possible consequences than SeaFoam or other fuel injection cleaners.

It's incredible to see how extremely low my NO emissions are now tho. I think I can attest that to 1. a badass OEM cat doing its job way better than I've seen with aftermarket cats, 2. brand new NTK oxygen sensors sending the right voltages to the ECU, and 3. a fully functional EGR system.