Time to smog the GTA again. In 2003 it passed with flying colors, but it did cut it close on the NOX numbers.

I'm looking for a little insurance and I'm wondering if there's anything I can do to improve the NOX numbers this time around?

Thanks.

 

Anything that will reduce combustion temperature.
ie. higher octane fuel, lower spark advance (allowed 6*+-3)
EGR clean and good working order and maybe an additive.(to the fuel)

 

Get this....
A year ago my smog test was cleaner than that of a test that was done in 1995 when the car was only 4 yrs old. Which I was all happy about.

I bought the car from my ex-girlfriend and it had to be smogged again and I failed. Turns out the cheapy high output cat I bought was a dud after a year.
Spend the money a good cat. Mine was like just under a hundred from JEGS.

After replacing the cat.... it passed but just barely.
But they put on a normal cat and man can you tell a difference! No power what so ever!
It's on my to-do list as far as things to fix on the car.

I wish I could produce some hard numbers for you, but can't find the smog papers. Sorry.

 

If you have room with the HC/CO's dept, you can fatten up the A/F this will lower NOX.

 

From what I understand, high borderline nitrogen oxide readings means that peak cylinder pressures during combustion are high. The EGR valve lowers NOX emissions by allowing some exhaust gases into the cylinder during combustion.

I'd check the EGR valve. The diaphram inside tends to get lazy as they age which can cause problems. The EGR solenoid is another thing I'd check as well. They usually don't go bad, but you never know. Also, I'd thoroughly check the vacuum tubes leading to the EGR valve and solenoid. One of them might have a slight hairline crack in it or something.

The only other thing I can think of would be the relocated MAT sensor. I remember an old post where you planned to relocate the MAT sensor from under the plenum to a location inside the intake boot. I guess the assumption is/was, by alot of people, that relocating the MAT sensor to a cooler location would enable the ECM to see a more realistic ambient air temp reading for more accurate fuel/spark timing control. However, I remember Vader stating that the MAT sensor is only for ECM control of the EGR solenoid on MAF cars. He stated that it had no other function other than controlling the EGR valve via the EGR soleniod based on intake air temp readings. Hope this helps.

 

Relocating the MAT sensor will make the AFR very rich without chip work.

 

Thanks for all the info.

The MAT sensor has never been relocated, so no problem there. EGR and EGR solenoid were replaced last year when I had the plenum apart to fix a fuel rail clog.

Looks like I'll fill up with some 91 oct. fuel and do a little freeway run before hitting the smog center.

 

If you have to wait in line to get your car tested, don't shut it off. You want everything up to temp for the best readings.

 

Make sure that the O2 sensor is working correctly (Rich/Lean switching and response time < 100ms) and that there are no exhaust leaks upstream of the CAT.

Cheap CATs tend to have the reduction portion go bad first, so that's a possibility.

Don't stress out too much about shutting the car off and letting it cool, by the time that the tech is actually ready to test it, it's been idling for an average of 5 minutes and it should be in closed loop by that point, then you get 90 seconds to get a stable passing reading, if the car can't het up with 5 inutes of idling and 90 seconds of dyno load, something is wrong.