Hi all: I barely pass from my last smog test 2 years ago. This year is smog testing year for my maxima and I did not pass. My problem is high CO and HC readings. My maxima has 187k miles and it runs great: 25mpg freeway and 22mpg combined. I have the following performance mods: Stillen Y-pipe (cali spec), O2 simulator for both down stream O2 (for fixing my P0420 code), suspension upgrade. I used to have a Stillen SC for 30,000 miles and the car was running super rich back then (AF 10:1). I removed it a while back and everything else is stock now.

No problem with NOX reading. Below is the reading:

15mph – barely pass
HC – max: 46ppm, my maxima: 42ppm
CO – max: 0.4%, mine: 0.4%
NOX – pass

25mph – failed
HC – max: 46ppm, mine: 52ppm (failed)
CO – max: 0.4%, mine: 0.7% (failed)
NOX – pass

I did some maintenance after the initial test and went back again – no luck. This is what I did:

Replaced: PVC, Spark plugs, oil/filter
Cleaned: MAF, intake

I performed some diagnoses with an ELM-based scan tool from eBay and it can do live sensor data. This is what I come up with:

Upstream O2 sensor readings (both banks) – between 0.1v to 0.9v (within spec)
MAF reading – 2-7 g/s idle and 7-30 g/s @ 25mph (within spec)
Short-term fuel trim reading - +/- 7 %. (looks normal to me)
Coolant sensor reading – 190F
Fuel status – closed loop for both banks

From my fuel economy and sensor readings, I think my car is running at optimal A/F ratio. The only parts that I haven’t tested is the cat. I removed it and it was not clogged. All the honeycomb stuff is still there.

I am suspecting that the Cat is inefficient but I can’t be sure. I am from California and I don’t want to spend $300 for a brand new CARB approved cat until I am 100% sure.

thanks in advance

 

Of course the Cat is inefficient! The P0420/P0430 means "catalytic converter efficient low" :-) By the way, the the cat(s) will be *lot* more than $300 in California (think $1500)

The Cali limits seems to be way stricter :-( Are you sure the guy who tested your vehicle did not put in 2010 as model year? My memory tells me that federal limits are lot more generous for 2000 year car but I could be wrong.

Having said that, I am stumped. The P0420/P0430 code is lot more stringent and having that code present alone will not lead to the borderline emissions. You did not post LT fuel trims. Also how is the upstream O2 switching? Have they become lazy? Are you running OEM spark plugs? New air filter?

I am really interested in finding out how you resolve this. All the indications are that you have unburned hydrocarbons in the exhaust. If you were really running rich, your mileage would be poor and the spark plugs would have been black. But if you have slight miss (i.e. marginal ignition coil), your HC/CO would shoot up. The ECM probably does not flag it unless the number of misses crosses some threshold.

If you end up throwing parts at it, this would be my order
0) Few double dosage of strong fuel system cleaner
1) New air cleaner element ($10)
2) OEM spark plugs from Amazon ($50)
3) new MAF tube from Dave B. ($100)

Oh, I almost forgot, you are the perfect candidate for "Cataclean"; it is on Amazon for $25. Go for it before anything else. I can say with 90% probability that it will be snake oil but you have to chance the 10% given your predicament.

Keep us posted!

- Vikas

 

I did little more google'ing and I see new Cats in your future :-( Following link is interesting.

http://www.fiero.nl/forum/Forum2/HTML/108478.html

 

thanks for the response.

The P0420 code I have is for the precat of bank 1. This precat is long gone after I installed the stillen Y. Not to mention my ECU is not updated with the new version from nissan. I replaced that down stream O2 sensors a few times and I finally got sick of it and went to the O2 simulator route.

I plan to just replace the main cat. I passed smog with the ypipe before. The CARB approved main cat is $300 compared to $100 for 49 states approved.

I did a vacuum check and everything seems fine. The reading from revving the engine to 3000rpm is normal. no back pressure from clogged cat.

I am pretty sure he entered the year correctly - it says on the smog report. Not to mention that my VQ40 Xterra which I smog-tested last year, has the same max limit. My Xterra has a 16 mpg but everything reads zero - I can almost breath the exhaust air from the tail pipe.

Since I don't have the precat for bank 1, it is all relying on the main cat. If my main cat is poisoned, that means the exhaust is not filtered at all and could lead to borderline emission. My number from last smog is not that great either, the smog guy had to play around with the probe in order to pass it.

I did measure the LT fuel trim but I did not remember the exact number, it appears to be normal, +/-3 - 7% IIRC. I have seen cars with bad O2 sensors that has a +25% fuel trim.

since my scan tool cannot do graphic, I can't confirm if the switching is good or bad. I would say it is good because each voltage reading is different. My friend's corolla that has a bad O2 sensor shows a steady 0.0v or 0.8v for a continuous 10 second.

I replaced the plugs recently and I used copper plug instead platinum. I heard copper burns better than platinum. The old plugs look fine except the gap was off. 0.036" instead of 0.044". I put ~90,000 miles on those platinums.

I will keep you posted. I think my max is not running rich because I did see positive number from the fuel trim and the low oxygen sensor reading indicate the engine is constantly adjusting between lean and rich.

one thing about the coil - I replaced my coils around 130k with the new ones that has a green dot on it. The old one caused detonation when accelerating. I still haven't find a way to test coil besides using the Consult II. any suggestion?


I have tried option 0-2 already. no luck.

the MAF was replaced around 110k. This was my third MAF. the first one died from boosting from the SC - at the very end of its life, I was running 14:1 with a 10psi of boost which is dangerous lean. The second one died from dirty K&N. I have switched back to stock intake since. Not to mention the smog guy does not like the intake air temp sensor dangling in the engine bay.

Thanks for suggesting the cataclean. I will take a look.

I think the only way to test if the main cat is the culprit is to use a test pipe and have my smog guy run the car again. If the reading from the test pipe is close to that from the main cat, that means my main cat is a goner. I think the main cat got enough miles and my super rich 11:1 from boosting has shorten its life as well.

Anton

 

Your hypothesis that running with bad pre-cats for years have finally killed the main cat makes perfect sense. If you read the other link I provided about a Fiero in CA, you could see that once he replaced the cat, his reading came back in single digits.

If the main cat is indeed $300, you might go for it. If you want the main cat to last forever, you will have to replace the pre-cats and run without the simulator to make sure you are not getting the P0420/P0430 codes. Alternatively your cat was destroyed NOT because of the P0420/P0430 but because of the running rich for 30K miles with Stillen SC. That actually makes more sense because most literature that I have looked tells me that just P0420/P0430 does NOT lead to bad emissions.

Try Cataclean; it is $25 gamble (I hope they ship to CA though!) but if that does not work, it looks like you will have to bite the bullet and get the new main cat. Look at the bright side, $300 is *lot cheaper* than $1500 or so that many cars would need to put dealer installed OEM converter.

You obviously are very knowledgeable and have the skills to wrench which puts 90% of the org'ers to shame (and that includes me!). My humble suggestion is if Cataclean does not work for you, new cat is the next logical step rather than monkeying around with other shot in the dark approach.

- Vikas

P.S. You don't need graphics on the scan tool. With our 5th generation cars, the sampling rate is low on the OBD and you barely get a couple of samples per second regardless of the scanner capability. If you can see the voltage numbers fluctuating, the graphics is superfluous. If your scanner allows, only select the single O2 sensor to get the maximum available sampling rate.

P.P.S. I did not know that you could actually check coils using Consult! I used to have P1320 for year or two before I was able to capture the offending coil. This happened twice. When the second coil went, I replaced all of them with the spark plugs (@142K miles!). The first coil went somewhere around 80K miles. Finding offending coil even with intermittent P1320 code is pain and if you don't have P1320, I have no idea how you would find the "undetected" bad coil :-)

 

Thanks for the link. I finished reading it. his problem sounds like mine.

This is what I found today to analyzer the my smog report. An air fuel ratio calculator.

http://www.smogsite.com/calculators.html#lambda

I entered my number from my last failed smog report and it came out an 14.34:1 AFR. This is not far from factory spec 14.7:1. This confirms my suspicion of an inefficient catalytic converter. The cat is an emission reduction device and it will not affect the AFR. If the rich fuel mixture is the culprit, I will getting say a 12:1 AFR.

I hope this new cat will last for another 180k miles. I plan to keep my O2 sensor simulator. I regretted that I went to the O2 sim route. If I were to do it again, I would install two O2 bungs after the main cat and use them to monitor its efficiency. This would have saved me a lot of time.

Thanks Vikas. I learned most of stuff from fellow members in this forum and trial and errors. When I bought my max, I know absolutely nothing about cars except changing oil. Thanks to members here and they are really helpful. The local members also spent their time to come dyno to help me tuning my max, giving me tons of advice, etc. Without them, I would keep pouring money to my mechanic. I am glad that I bought my maxima. The "post-sale" support is much superior than other cars that I purchased.

that's one of the issue that encountered with the ELM based ebay scanner. I finally got it to work with scantool.net v1.13 software. You are right, I have to monitor a set of samples each time. I was able to see a continuous reading of the sensors that I need to diagnose. I use the ELM327 with USB interface. So far, I can only use the scantool.net software. Nothing else will work with the maxima due to max's low sampling rate.

http://cgi.ebay.com/ebaymotors/OBD-I...motiveQ5fTools

142k miles on the spark plugs? Can you even turn that thing to remove it? I bet all the antiseize were all dried up! Mine was! took me a while to remove spark plugs from cylinder 6 - I thought I jumped a thread. It was so tight and almost like I am giving a hummingbird a prostate exam.

yes, you can check the coil condition with a Consult II. It is under the P1320 code diagnosis section of the FSM. That was the code that I was getting and there is another way to test the resistance with a multimeter and it was from a thread from a member here. It does not work for me and I couldn't locate the defect coil. Ended up replacing all of them.

have a good one!

anton

 

142K miles on the original plugs; the gap had grown by at least 50%. The car was still running great with those plugs. The plugs came out without any trouble.

The plugs from my 99 Odyssey came out at 152K and they were in *excellent* shape. NGK laser platinums are just amazing.

This is the plug from Maxima.
http://a.imageshack.us/img28/5499/usedsparkplugo.jpg

 

Anton,

What happened? Any update to your saga?

 

LOL! I recently changed plugs on my G35 coupe, at about 100K miles. Factory spec is .044", and the old (original) plugs came out with the gaps eroded to about 0.80". Needless to say, it runs a bit better now.

 

Vikas: I replaced the main cat and brought her in for smog last Monday. I passed smog with flying color! HC reads 7ppm compared to 52ppm from last time and CO reads 0.03 percent compared to 0.6%. The CO2 reading increases to 15.1% compared to 14.3%. Low CO2 readings and high HC/CO readings from the failed testing indicates that cat is not effective in oxidizing HC and CO to CO2. I passed the smog with Y pipe, 1 precat (bank2) and O2 simulator.

The main cat is a carb approved direct fit cat and purchased from http://www.catalyticconverterwarehou...-converter.htm.

$300 for the CA cat compared to $90 for a Fed cat.

I asked the company for the differences between the CA cat and Fed cat. They said it costs a lot more to have CARB to review and approve a manufacture. CA cat also has more honeycomb material than the Fed Cat.

The install of this cat is a killer. It does not come with any bolts, no biggie. But it has a 12mm O2 sensor bung in the back and it is impossible to find a plug for it. I ended up using a M12 bolts with 1.25 pitch and I had to cut it short with a hacksaw. Even though it is a direct fit, it does not fit well. After I installed it, the exhaust pipe after the Cat and before the resonator keeps hitting the bolt-on frame when I roll off from dead stop.

Here is what I have learned. Hope this will help .orger when it comes to failing smog.

- Always asked your smog guy to do a manual check before a real smog test. Once it failed, the data goes to DMV. If your car is failed as a gross polluter (%200 above the maximum reading), you will have to go to a Gold shield test center and smog check will become tougher.

- Do all maintenance before smog check, Oil change, Spark plugs, PCV valves, clean throttle and run fuel cleaner. Leave oil change as the last step because any fuel additive can contaminate engine oil and make smog failed.

- Tires should be properly inflated before running the dyno smog.

- Any Check engine light will failed smog. Clear it with a scantool or unplugged battery does not mean it is gone.

- Catalytic converter is the last thing to replace when diagnosing smog problem. You will need to make sure engine is in optimal running condition. A poor engine condition will shorten the life of a good cat and the same problem will eventually resurface.

- Check AFR from failed smog result by using the AFR calculator from my early post. If the AFR is reading close to factory spec 1:14.7 and the car still fails smog, this could mean the cat is not effectively converting HC/CO to CO2.

- Scan the car with a scantool that does live readings of sensors to check
1.O2 sensor voltage switching (should be fast switching between 0.1v - 0.9v)
2.Short term fuel trim (indication of O2 sensor function)
3.Fuel control (if car is in open loop due to failed thermostat, it will not pass smog)
4.MAF function (should reads 15% when running @ 25mph and 2000-3000rpm).

- Do a vacuum check will give you valuable info of your engine condition.

- A borderline fail of HC (<100ppm) and CO (<1.5%) may indicate an ineffective cat. (credit, eHow)

hope this will help.

happy Friday.

 

Wow! Great information, somebody needs to make your reply a sticky!

I take it that you decided not to gamble on my suggested snake oil remedy, Cataclean? Come on, it was only twenty five bucks :-) Now I will have to wait for another sucker!

- Vikas