Failed Emissions Test, Nox

[richy z]

I was just curious, would running 89 gasoline instead of 91 cause me to fail only the NO portion at 15 mph max 748 meas 919. Thank you, any input would be great.

[jsi4u2nv]

NOx is caused by high exhaust temperatures... the EGR system is what is used to control it. I would think your EGR valve is clogged ir not operating correctly.

[92Lex]

NOx is caused by many things, not just a defective EGR valve. There are a ton of things that can cause elevated NOx levels like; a bad EGR valve, excessive internal carbon build up, warped cylinder head, decked cylinder head, low fuel pressure, vacuum leaks, defective MAF sensor, defective O2 sensors, defective catalytic converter, lean a/f ratios, defective EGR modulator, clogged EGR passages, clogged intake manifold EGR passages, defective ECU, advanced timing and the list can go on forever.

[sc300tt]

ive seen people run RXP through there car and it would come back and pass the test with flying colors. just make sure it get it all out of your tank before going back to test or you will fail.

[infamous1212]

I had the same problem on mine and it turned out to be that the EGR was stuck closed.

[92Lex]

ive seen people run RXP through there car and it would come back and pass the test with flying colors. just make sure it get it all out of your tank before going back to test or you will fail.

Does Texas test for NOx emissions? I thought that you guys still use the "two speed idle" test?

[allthatisman]

My buddy has a 92 sc400 with 152k... fairly good condition, runs excellent. He went to smog it and get it registered here(it's from Florida) and it passed everything else with acceptable margins, but showed a really high NOX reading. Wouldn't a bad EGR cause the car to stall out and run, not well? Any thoughts? Like I said, the car runs and idles like a brand new car... maybe it needs some sort of additive?

[92Lex]

An EGR valve that is stuck partially open will cause poor idle/acceleration. If the EGR diaphragm is ripped, or the car has a defective modulator, then you probably wouldn't notice any driveability issues.

[sc300tt]

texas does an obd2 test and for older makes they put on dyno and check all readings. only AWD cars get the 2 speed idle, or cars that cannot turn the trac control off.