Hey guys, I live in windsor ontario canada. I have a 95 Z28 AT and I failed my etest today!!

The car passed everything with flying colours except NoX the limit was 408 and it read 1048, the car has a built trans and a hypertech power programmer. also there is a crack in the rad but its not leaking very bad.

Can anyone shed some light on what lowers NOx and if the hypertech programmer or the crack in the rad could have caused a fail?

 

Power programmer = Turn it off ~ Get reinspected. Sounds too rich so heat up the NoX is lean it out stock in other words, smog stock fuel curve.

 

High NOx readings are usually due to a defective cat. They can also be caused by cylinder temps being too high or the EGR system not operating correctly. You can try taking the Hypertech tune off and getting it retested, but if it fails again after that you'll probably need to look at replacing your cat.

 

That year model did not have the extra o2 sensor you may not have a cat under there. Either way you will have replace the cat. I think the EGR is for cold start emissions.

 

just changed my EGR valve. carbon build up was rock solid.

 

The EGR helps on cold start, but it's also fairly active at highway/cruising RPM/engine load.

 

If working properly the EGR is always closed at start up, idling and WOT. It is only supposed to open at during normal driving. The car will fail the sniffer test, high NOx, if the valve remains closed (or plugged up) during the cruise test. A closed valve increases combustion temp causing the excessive NOx. A lean fuel mixture and excessive spark advance (perhaps due to the Hyperthech programming), will also increase NOx production. Also using low octane fuel in a high compression engine will result in high NOx, due to pinging or spark knock. Of course if the cat is bad, nothing short of replacing it will help much.
As said previously, restore the the factory tune, clean out the EGR valve and passages, make sure the EGR operates, fill the tank with premium fuel and try a retest. You may also try a can of cat cleaning stuff, but it has never done much for me.