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Old 02-21-2008, 07:21 AM   #1
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High NOx reading during emission test

Hello,
would anybody have any ideas on why the NOx readings are way out of scale?
The vehicle is a 99 with V6 in it. It was fully wormed up before the test (but this was done during some cold days up in Toronto and the vehicle was parked of about 10 minutes before the test).
It can not be an egr valve, as there is none.
What I'm thinking is that it might be the rear Oxygen sensor, but that is just my guess.
Any imput will be greatly appreciated.
Thanks!
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Old 02-21-2008, 12:24 PM   #2
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no egr ?
someone mess with it, it isn't stock ?

the job of an EGR valve is to reduce NOX. if you don't
have one, there is your answer

you answered your own question.


EDIT: I am wrong and stupid..../head in sand
------------------------------------------------------
When combustion temperatures exceed 2500 degree F., atmospheric nitrogen begins to react with oxygen during combustion. The result is various compounds called nitrogen oxides (NOX), which play a major role in urban air pollution. To reduce the formation of NOX, combustion temperatures must be kept below the NOX threshold. This is done by recirculating a small amount of exhaust through the "exhaust gas recirculation," or EGR. valve.

The EGR valve controls a small passageway between the intake and exhaust manifolds. When the valve opens, intake vacuum draws exhaust through the valve. This dilutes the incoming air/fuel mixture and has a quenching effect on combustion temperatures which keeps NOX within acceptable limits. As an added benefit, it also reduces the engine’s octane requirements which lessens the danger of detonation (spark knock).

Last edited by edzo; 02-21-2008 at 01:10 PM.
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Old 02-21-2008, 12:39 PM   #3
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Quote:
Originally Posted by edzo View Post
no egr ?
someone mess with it, it isn't stock ?

the job of an EGR valve is to reduce NOX. if you don't
have one, there is your answer

you answered your own question.
Um, no, it's stock and there is no EGR valve on the 3.4L motor so he's right in saying that can't be the cause.

Your issue maight be:
1) Front O2 or A/F sensor (replace)
2) MAF (clean well with brake cleaner)
3) Exhaust leak
4) Vacuum leak
4) Injectors

Were there any OBD codes along with this high NOX reading?
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Old 02-21-2008, 01:09 PM   #4
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If you have all the numbers from your test it would help to post them. High NOx if from high combustion temps. Need to know if HC, O2, CO2, and CO are high/low or normal.
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Old 02-21-2008, 01:09 PM   #5
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ok then I wuz wrong. I don't know the 3.4 well enough

cats burn nox into water and co2 and co. bad cats perhaps ?

engine is probably running lean, ergo, hot. cleaning the MAF may help.

CRC makes a MAF specific cleaner you can find in most parts stores,
whatever you use to clean MAF must leave no residue.

Last edited by edzo; 02-21-2008 at 01:16 PM.
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Old 02-21-2008, 01:32 PM   #6
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Cats don't burn NOx. So don't worry about the Cats. Hot combustion is the key and we need to know all 5 gas measurements. May be lean condition but the 5 gas measurements will tell.

Quote:
Originally Posted by edzo View Post
ok then I wuz wrong. I don't know the 3.4 well enough

cats burn nox into water and co2 and co. bad cats perhaps ?

engine is probably running lean, ergo, hot. cleaning the MAF may help.

CRC makes a MAF specific cleaner you can find in most parts stores,
whatever you use to clean MAF must leave no residue.
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Old 02-22-2008, 04:01 AM   #7
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Quote:
Originally Posted by bwhyit View Post
Cats don't burn NOx. So don't worry about the Cats. Hot combustion is the key and we need to know all 5 gas measurements. May be lean condition but the 5 gas measurements will tell.
X2

Having all those numbers would help on the diagnosis.
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Old 02-22-2008, 04:25 AM   #8
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Good morning All,
thank you for all the suggestions.

Here are the readings from the test (there were only 3 items measured, aside from RPM and Dilution), please take a look at the attachment.

I did connect an OBD II reader and got no codes . I have cleaned my MAF sensor about a year and a half ago, but I remember it threw a code at me when it was "dirty" that time.

I have also spoken to one of the guys at the dealer, he suggested it might most likely be an O2 sensor that's down from the catalitic converter.

Best regards!
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High NOx reading during emission test-emissions_test_readings.jpg  
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Old 02-22-2008, 04:31 AM   #9
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You said it was parked 10 minutes before testing?

Drive it on the highway for an hour before testing. Thats what I was told to do, and it worked.
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Old 02-22-2008, 09:22 AM   #10
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Quote:
Originally Posted by silverunner99 View Post
I have also spoken to one of the guys at the dealer, he suggested it might most likely be an O2 sensor that's down from the catalitic converter.
Possibly the one in front of the converter, but definately not after since that only checks the condition of the cat which is obviously working fine given the numbers you posted. Go through the list I mentioned and eliminate the items one by one.
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Old 02-25-2008, 12:50 PM   #11
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Quote:
Originally Posted by MTL_4runner View Post
Your issue maight be:
1) Front O2 or A/F sensor (replace)
2) MAF (clean well with brake cleaner)
3) Exhaust leak
4) Vacuum leak
4) Injectors
Hello MTL_4runner,
I have few questions for you (or anybody else that would like to answer):

re. #1) What's an A/F sensor?
re. #2) For the MAF sensor, shouldn't I use the electrical cleaner instead?
re. #4) How would I check vacuum leak?

Thanks!
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Old 02-25-2008, 12:58 PM   #12
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Quote:
Originally Posted by silverunner99 View Post
Hello MTL_4runner,
I have few questions for you (or anybody else that would like to answer):

re. #1) What's an A/F sensor?
re. #2) For the MAF sensor, shouldn't I use the electrical cleaner instead?
re. #4) How would I check vacuum leak?

Thanks!
an A/F sensor is just like an O2 sensor, but it is electrically different and
sends different voltage to the ECU from in front of the cat. California emissions have them, federal just have 02
it costs about double what an o2 sesor costs. stealership sold me one the ohter day for 217 and the
o2 sensor is 140.

so if you have a California emissions, it is an A/F sensor. definitely not interchangeable with an O2 sensor.

a lot of people have a bad A/F, install an o2 sensor by mistake, and reset the ecu. the car will run wicked
awesome for about 1/2 or a full tank, as the ECU gets a good heater reading from the o2, and thinks
the engine is rich. short term trim and long term default trim fights and runs the engine wicked crisp and
wicked lean, giving you amazing mileage...for a short time. the amazing mileage comes with a huge emissions
penalty of high nox... [as you hear your cats crackle and pop from the higher heat as it burns off any carbon
from the previous problem of a bad sensor and rich condition. you just cleaned up your cats a bit...]

then the computer finally decides the signal pattern is bogus, switches to cripple mode and runs you
rich, putting you back to square one.

anyhow....A/F is air fuel and it gives the ECU a more exact ratio of oxygen, whereas an O2 sensor just tells
the ECU you are either rich or lean, no inbetween. california ECU is programmed to use A/F signals, [but can handle
the signals from a mistakenly installed o2 for a short while, it treats it like rich, then broken.]

Last edited by edzo; 02-25-2008 at 01:08 PM.
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Old 02-26-2008, 04:16 AM   #13
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Quote:
Originally Posted by silverunner99 View Post
Hello MTL_4runner,
I have few questions for you (or anybody else that would like to answer):

re. #1) What's an A/F sensor?
re. #2) For the MAF sensor, shouldn't I use the electrical cleaner instead?
re. #4) How would I check vacuum leak?

Thanks!
1) Like an O2 sensor, but they are not interchangeable
2) No, electrical cleaner doesn't work even half as well.
3) Look for broken or cracked hoses then with the engine running, spray carb cleaner near suspected leaks and listen for a change in idle speed
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1996 4Runner SR5 4X4 Auto

Deckplate Mod, Hayden Tranny Cooler, Amsoil Air Filter, OME 881/906 N86C/N91SC Lift

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Old 02-26-2008, 05:15 AM   #14
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Thanks for the info!

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Old 02-26-2008, 05:38 AM   #15
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Quote:
Originally Posted by bwhyit View Post
Cats don't burn NOx.

incorrect

A three-way catalytic converter has three jobs

1. Reduction of NOx to nitrogen and oxygen: 2NOx → xO2 + N2
2. Oxidation of CO to carbon dioxide: 2CO + O2 → 2CO2
3. Oxidation of unburnt HC's to carbon dioxide and water: 2CxHy + (2x+y/2)O2 → 2xCO2 + yH2O

Last edited by edzo; 02-26-2008 at 05:40 AM.
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Old 03-10-2008, 04:34 AM   #16
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So it passed the emission test.....

I have done two things:

1. Cleaned the MAF sensor
2. Replaced the rear oxygen sensor

I also put the high octane fuel and made sure that the car is fully wormed up.

Thanks to everyone who helped!!!
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Old 12-02-2008, 06:25 PM   #17
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SILVERUNNER99

I have the same problem with my 4 runner. Did you said you replaced the oxy sensor before the cat or after the cat? (front is before the cat) ? (REAR ? is after the cat) WHICH ONE?

Thank You
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Old 12-02-2008, 06:25 PM
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