car failing emissions NOx
 

a car in perfect shape, everything properly tuned and all sensors working, and EGR working properly is failing emissions on high NOx. everything else is passing....

using correct gas (but etested on both regular and supreme), using the correct plugs... EGR guaranteed to work and is not clogged. plugs read hot as well, as in the EGTs are too hot. correct fuel pressure.

would a new catalytic be in order, or does a car with a bad catalytic converter fail on ALL tests??

in case you were wondering, the car in question is my old 93 saturn wagon twin cam 5 spd with intake header exhaust.

Ignition timing too advanced. That's usually the problem with a high NOx rating. Unless it's digital ignition then, IDK :confused:

EDIT: Catalitics only deal with HC emissions normally.

thats a tough one bruno..

nox is from high temperature combustion. What degree thermostat is being used? that could be something to consider.. is it running lean?

a cat. oxidizess hc and co, not NOx.

So your cat is fine.

A failed thermostat that stays closed will give you high HC and CO reading; but if it stays open, perhaps if will give you this particular problem?

If all else seems fine then it's gotta be running lean.
Throw in a new o2 sensor and it'll pass.
They can't be that expensive for the Saturn since it prolly uses a 1 wire o2 sensor anyway.

im sure he would notice the temp skyrocketing if the stat is failing.... On the other hand its a cheap and easy changed part thats never a waste of money....

he could be using a high temperature thermostat

O2 sensor and thermostat (dealer item, not aftermarket) are both brand new.

ignition is digital (coil packs)....

I've considered all the easy possibilities already. I'm led to believe.... somehow.... that either carbon build up is causing increased compression (but with such high temps, it should have burned off), or that the injectors are in need of replacement.

The techs on the saturn boards are also stumped.

our wise friend google says the following:

Misfire condition
Malfunctioning or improperly adjusted EGR valve
Failed oxygen sensor
Leak in exhaust tubing upstream of converter
Excessive carbon deposits in combustion chamber
Improper spark advance
Blocked coolant passage
Overly lean air-fuel mixture
Damaged cold air duct
Corroded or damaged engine sensor electrical connections


because all the plugs look the same, I can eliminate the blocked coolant passage I think, and I know the car is not overheating... new rad, hoses, thermostat... and the fan is wired to be on all the time.

wow..

my advice Bruno.. get methal hydrate, dump it in the tank and go for the e-test and pass it.

or just retard the timing a deg. or two lol

cant retard coil packs.... retard :p

vaccum leak is a possibility,
is it the OEM EGR? if so take it out and clean all the carbon out of it, run a motorvac on the engine (cleans out injectors and all the carbon from the motor) try putting the stock air box back on, since its more restrictive it will make the car richen up a bit.

what do the numbers look like? is it failing lots for NOx? and is it driving or idle test where its failing?

If its carbon buildup...Take it for an italian tune up and see what that does.

it's a dealer supplied brand new EGR valve and solenoid and vacuum lines. I replaced the entire system last year, and tested it many many times, it works (as in the ECU sends it signals and it does what it's supposed to). I've tested vacuum with a gauge, it indicates no leaks. I don't have the stock air box anymore.

I'll have to locate the emissions report for exact numbers...

hmm too bad u dont have the stock air box, but definately find the papers and let us know man :)

stutup wanabe mechanic:richslap:

well what car are we dealing with here....I hate egr ****

anyway check for leaks on the intake side of things could be getting more unsensored air causing lean condition.

maybe try putting a colder range of spark plug in there


or new gapped plugs

but I woudl throw a new o2 in there personally


NOx is a bitch to get rid of sometimes but I woudl start replacing **** like o2 and check for leaks in intake system.

thanks everyone for your input

40 km/hr test

test limit reading
HC ppm 75 37

CO % 0.42 0.05

NO ppm 0576 1517 Fail


Curb Idle
test limit reading
HC ppm 200 42

CO % 1 0.04

NO ppm n/a n/a

nox
 

how often do u drive the car? and when u do drive is it short trips ? What i did and I was in a similiar situation go to canadain tirew buy yourself some GTP ( guaranteed to pass) and foolow the instruction make your appointment and go for a really nice blast on the highway for about 1 half hour and have it tested nice and hot! let me know what happens

saturn sw2

MAP reading (not MAF), therefore no unmetered air is possible.

yeah, I gotta find out which ones will be colder, looks like a call to NGK is in order.

O2 is new

one other possibility I thought of was that the previous owner may have chipped it, which would advance timing of course, but the HC levels don't indicate a richer mixture which is also something a chipped ECU might exhibit.