View Full Version : Emissions tests

01-04-2005, 01:14 AM
Nitrogen Oxides are the devil.

The first time I took my 91 GT through emissions I failed due to NOX emissions. First test results were HC 0.42/1.00, CO 10.13/12.00, NOX 2.72/2.50. Ok, so I'm close, all I need to do is bring down NOX by less than 10%.

In goes a new O2 sensor (because it hasn't been changed since I got the car two years and 40,000 miles ago), new NGK plugs, new wires, cap, rotor, air filter and an oil change. Checked the timing, put at 10 degrees. I had run a bottle of the guaranteed to pass stuff through my tank before the first test since I saw the results of a friend's 70's El Camino brought down to almost no emissions whatsoever after using it.

Premium gas in the tank, and I retest.

HC 0.46/1.00
CO 3.37/12.00
NOX 7.09/2.50 (WTF? :eek: :madfawk: :eek: )

So what do I do to bring the NOX emissions down?

Cliff notes: NOX emissions are through the roof after tuneup maintenance

01-04-2005, 05:13 AM
did you check your cat converter?maybe it's time for a change...that's one of the main purpose of the cat...to reduce nox...so i would check that..

01-04-2005, 05:19 AM
Advance your timing a bit, and make sure to let your car run for a decent length of time before the test. Never test your car cold!

01-04-2005, 03:10 PM
Run your engine hot for awhile before bringing it in for testing (1/2 hr on the highway). This will get your cat working at peak performance in elimminating NOx. Premium fuel helps too.


01-04-2005, 05:02 PM
Yeah, it had plenty of time to warm up. Yay for rush hour traffic on the way home to the emissions station. Granted, it was a very cold day (at least for Arizona) yesterday.

As for the cat...aside from making sure it's there (which it is), how do I check it? I can't do much other than make sure that nothing is falling out of it, can I? And if I do get a new one (looks like I'll be headed that direction next unless I can find a big clog in my EGR pipes), any reccommendations?

01-04-2005, 06:28 PM
I had the same prob w/ my celi passing the NOx in AZ.
I replaced the cat, corrected the timing, replaced the intake tube, cleaned out my EGR components, replaced some sensors(O2,temp sensor, and the one by the temp sensor) and i passed w/ flying colors.

01-04-2005, 06:37 PM
Lower NOx = more octane. Go fill up with 100 or a few gallons of tolulene, I passed inspection with my 165 with no cats and no egr like that and I live in cali, the land of the smog nazis :D It will bring up your HC emissions a little, but so long as you dont have misfiring or other eng problems you'll be fine.

More NOx means you have really high combustion temps btw... could also mean you're running too lean.

01-04-2005, 07:03 PM
Just had one other thought - a few months ago my car had a small run-in with a low center median in the road while I was dodging a girl who pulled out in front of me. Mostly cosmetic damage but the exhaust pipe, just past the exhaust manifold and before the cat, has a decent sized dent in it. No leak, but a dent. Could that have something to do with it?

And can someone give me the recipie for the best mix of gas and toululene stuff so I can pass? I remember seeing it before at celica.net before the kaboom.