So, I went and took my ride to eCheck, I was feeling confident, just replaced spark plugs, fuel filter, seafoamed and fuel injector cleaner. I thought I had a nice shot to pass.

I get my readings..

HC - PASS (But high)
CO - PASS with flying colors
NO - FAIL (3700 ppm) Legal limit is (1100)

Any ideas?

 

Among the potential causes of non-compliant NOx readings are:

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
Failed or malfunctioning catalytic converter
Corroded or damaged engine sensor electrical connections

Regardless, there is a lot more to emissions than running Seafoam and new spark plugs...

 

If you want help you gotta post the VIR.

 

it's usually the catalytic converter.. Get a new one!

 

My 94 Civic EX with about 311k failed the 15mph test since the NOX was high. Got a new o2 sensor and cat and the NOX went down from 2629 to 154 after the installation. At the actual smog test it read at 207.