Emission almost fail, high NOX, low HC, low CO

[PandaBear]

Just did a smog check on my 95 Corolla with 200k today, the smog guy had to do it twice because he said the first time failed.

Numbers are very low on HC and CO, single digit ppm but the NOX are very high (around 500ppm) and near the limit. This is both for 15mph and 25mph so I think there must be either a vacuum leak, a clogged EGR, a plugged fuel filter, a leaking PCV, or a cracked header.

I'll have 2 years to fix it and since it passes I'll just replace / clean as much as I can as preventive measure, like new fuel filter, new PCV, clean the EGR, check for vacuum leak, etc. Make sense?

 

[HTSS_TR]

Some years ago my LS400 barely passed smog check, I think the NOx was near the limit. Two years after that I used Redline SI1 fuel system cleaner a couple tanks before smog check and it passed will ease. After that I changed the fuel filter and had no problems with smog check at all. One more thing, I drove at least 15-20 miles on highway before go to smog station to get the engine fully warm before test.

 

[javacontour]

If you have the 1.6L, I'm not sure it has an EGR. Things in the People's Republik of Kalifornia may be different. I believe the 49 state emissions version of the 4A-FE didn't have an EGR. The 1.8L 7A-FE does have EGR in the 49 state version.

A cracked exhaust manifold is a common failure on these cars. I had the manifold replaced on my 1994 Prizm while I owned it.

 

[Vikas]

From what I have read over the internet, once you rule out simple and easy stuff, you end up having to replace the catalytic converter to fix high NOx.

- Vikas

 

[Trav]

High NOx is caused by high combustion chamber temps.
A new cat will generally not fix high NOx especially if no P420/430 code is present, some of the causes.

EGR issues, plugging or vacuum signal failure.
Cooling system problems
Incorrect timing or spark advance
Carbon deposits in the combustion chamber
Incorrect spark plug heat range
A tired rich biased O2 sensor may also cause a lean mixture without setting a code (not common but happens).
Vacuum leaks will normally tend to make the fuel system to go rich causing high HC and O2
Modified exhaust systems with high flow muffler can cause EGR issues on back pressure dependant systems.

I would look at the EGR (if used) system closely on this car.

 

[Eddie]

The first thing I would do is run a "Fuel System Cleaner" like Techron or Redline. Do a long 25 + miles highway run with the cleaner and use the full take of fuel up before refueling. This of course after checking the EGR, PCV and vacume leaks etc.

 

[PandaBear]

It does have EGR. The exhaust manifold was replaced (due to crack) about 4 years ago and I haven't seen a crack yet (will do a spray test to confirm.

 

[mechtech2]

Panda-
EGR and maybe high engine inlet temps are first to look at.
All your other things are good to do , but don't apply.

 

[morris]

i have read but dont know for sure if it works. have about 5-8 gal of gasoline in the tank. put about 5 gal of methanol in. go to the test site, get tested. it WILL run bad then after the test put a bunch of gasoline on top of the methanol. like i said i dont know this will work.

 

[JHZR2]

Originally Posted By: Trav
High NOx is caused by high combustion chamber temps.
A new cat will generally not fix high NOx especially if no P420/430 code is present, some of the causes.



My 91 BMW 318i had exactly what was described, high NOx, low everything else. It doesnt have an EGR. I went through everything, turned out to only be a bad cat. Nothing else. Spent a lot of $ chasing a bad cat, including trying a generic one. A NEW generic cat has as poor conversion efficiency as an end of life OE cat.

Put on a BMW OE catalyst, and NOx went from ca. 1100 to 2. I have a few threads on here from a few years back describing all this and the dyno test results.

 

[Trav]

AFAIK pre OBD II BMW systems with the round plug (pre OBDII in general) did not have cat inefficiency codes, if they did you would possibly have got a P420.

 

[tom slick]

We need all of the numbers from of the test.

 

[PandaBear]

15mph

rpm 1856
co2% 14.7
o2% 0.0
HC(ppm): max 93, avg 27, meas 9
co%: max 0.57, avg 0.07, meas 0.06
no(ppm): max 504, avg 167, meas 500


25mph

rpm 1845
co2% 14.5
o2% 0.1
HC(ppm): max 59, avg 16, meas 7
CO%: max 0.55, avg 0.07, meas 0.12
no(ppm): max 542, avg 146, meas 452

 

[mechanicx]

Originally Posted By: Vikas
From what I have read over the internet, once you rule out simple and easy stuff, you end up having to replace the catalytic converter to fix high NOx.

- Vikas


That's what I think too. If the cat was working well I don't think the NOx would get that high even if there was some little issue with the engine upstream. I'm not an emissions expert so I could be wrong. It wouldn't be a bad idea to run fuel cleaner and check EGR function etc but I wouldn't be surprised no issue is found there.

 

[Trav]

This is a good read.
http://discountconverter.com/tech-tips/news_page.cfm?Key=catalytic_converter-&News=216

Of course a cat can go bad but when i was working with the RMV for the company that ran the emissions program in MA we had lots of cases where owners were looking for a RMV emissions waiver.
Many of these were after a cat replacement failed to cure the emission fail, we estimated by going over the data that 75-80% of the investigated cases were replaced unnecessarily.

Toyota's including 95 model year were able to monitor the cat (not mandatory til 96)and will throw a cat code quicker than any other car i know of if anything isn't up to snuff.
As i said i'm not saying a bad cat is impossible but on this particular car i wouldn't part with my money to quick for a new one before everything else is eliminated.

OP take a temp reading before and after the cat directly at the inlet and outlet pipe if there is about 100f difference @ 2500 there is a catalytic action taking place more or less confirming a functioning cat.

 

[Vikas]

Panda,

If we were to give you some pointers, are you in a position to hook up your vehicle to the machine again to get the readings cheaply? If not, forget about it now and worry after two years.

Who knows, your Apple stock options might quadruple (sorry if I mistake you for another BITOG'r) and you would be buying that Ferrari you had always wanted and trading in this vehicle

Seriously, without the ability to get the new numbers, there is very little that you should do *at this stage*.

- Vikas

 

[PandaBear]

Originally Posted By: Vikas
Panda,

If we were to give you some pointers, are you in a position to hook up your vehicle to the machine again to get the readings cheaply? If not, forget about it now and worry after two years.

Who knows, your Apple stock options might quadruple (sorry if I mistake you for another BITOG'r) and you would be buying that Ferrari you had always wanted and trading in this vehicle

Seriously, without the ability to get the new numbers, there is very little that you should do *at this stage*.

- Vikas


No I don't have a machine to hook up to read emission number till 2 years later (when I smog check).

The stock options days are gone, there is no more big options unless you are a big shot (VP or above). Even if I do have options, I'll still be driving a corolla

Just trying to get the car running optimally, I think it is ok so far but if it could run better because something may be busted, why not.

 

[Vikas]

I know *you* don't have the machine but if your mechanic has it and if he will give you the unofficial numbers for a 6-pack of beer, you will have more options.

Otherwise, do the usual stuff, including some kind of carbon cleaning procedure (such as BG, 3M, Seafoam etc) and/or catalytic converter cleaning procedure (you can find them on the web; not sure if they really work though). If you have high carbon build-up, it will lead to high combustion chamber temperatures leading to more NOx production from the engine. Given your low HC and CO, your fuel tunes and ignition systems are in great condition, so do not go in that direction. If there is no EGR system on that vehicle, then the first two items I mentioned are the only things that you can pursue.

If de-carboning is successful, you would get better performance and lower emissions. If you really need the converter (more likely on that old of a vehicle) there is no point in getting a new one at this stage (unless you happen to be hug the trees greenie It is going to cost you a lot for OEM one as you are in KaliForkNia!

You already know how I feel about 3M DIY kit even though I have never used it personally! If I were in your shoes, I will try that before doing anything else.

- Vikas

P.S. Aren't Bitten Fruit employees giving you dirty look when you bring your jalopie in their parking lot??

 

[PandaBear]

Originally Posted By: Vikas
P.S. Aren't Bitten Fruit employees giving you dirty look when you bring your jalopie in their parking lot??


There are 2 types: those who buy the best and flashiest (i.e. numerous Ferrari, Lamborghini, Maserati, Tesla, S Class, R8, etc), and those who are minimalists.

and, like all farms, there are wealthy land owners, and there are peasants.

 

[ARB1977]

Thank god i dont live in a smog state anymore. If the cat goes ill gut it and run a O2 simulator to trick the computer. Performance will not change as long i have a good O2 sensor.