I took my car to get it smogged today, and it surprisingly failed. The car passed everything but the NO(PPM) test, where I got 1080 and the max allowed is 487. This was at 15 mph, while at 25 mph the car passed, got 362 out of 774.Now, my car is a 96 ej8 with the stock motor, except for aem sri, edelbrock header, and apexi ws2 exhaust.I have to register this car in a couple of days and need to pass soon. Any ideas on what could be the problem? Cat?

 

If the engine has had a recent basic tune up and the primary O2 sensor is fine, then I also would suspect a problem with the catalytic converter.

 

Recently i replaced the spark plugs, wires, rotor, cap(not yet)and pvc valve. I havent replaceed the fuel filter. COuld that be the problem? How do I know if the 02 sensors are okay? I have no CEL's.

How do I check for catalytic converter problems?

 

Possibly.

A scan tool would be necessary.

A badly clogged cat might cause a loss of power; however, a cat on the way out might simply show the high NO levels that you are seeing.

 

Here is the sheet from the smog check.


Why would the nox be so high at 15 mph, but pass without problems at 25 mph?


Where would I get this scan tool to check the 02 sensors?

Thanks

 

Check the EGR system if that car has one. It could be a bad EGR valve, passages clogged with carbon, or the aftermarket header may not be allowing exhaust to enter the passage thru the head back to the EGR valve.

Otherwise probably the cat itself. Again aftermarket exhaust could be a problem because if there are no heat shields on it, the exhaust may become too cold on the way to the cat for it to work effectively.

 

Sorry, I missed this important difference. This suggests that the catalytic converter is probably okay.

Yeah, focus on the primary O2 sensor. Check whether any of the auto parts chain stores will rent you scan tool that makes live O2 sensor readings. Alternatively, try replacing the primary O2 sensor.

 

When you run rich, as usually is the case with a bad O2 sensor, NOx emissions actually go down, but HC and CO become excessive.

 

I assumed that a bad O2 sensor might also be able to make the engine run too lean.

Other potential causes for high NO are a faulty EGR system, coolant temperature sensor, or out of spec ignition timing.

 

In what state do you live in Bro...They must suck!!!Here in California when you do your smog test and ifit fails they tell you right away and even on the print out it says what caused it to fail.