I am so disspapointed. Today I took my 300zx for smog check and it failed. the NO (PPM) failed:

15 mph 424 57 787
25 mph 711 50 1008

They guy at the test station told me i may need a new catalytic coverter or check my EGR.

Before taking my car for the smog check, i had a bad O2 Sensor. I repaired it, after I repaired it (had broken tip), the light did not come back on.

These are the possible problems:

bad o2 sensor
bag EGR valve
bad cat
bad timing
dirty injectors

I will post my results with what i did once i pass this stupid test.

------------ 2 days later ------------
I dediced to check the catalytic coverter per the advice of the tech at the emission place. I had to remove the exhaust to check this. When I removed the exhause i saw that one of the Oxygen sensors was broken. So i dediced to replaced both of them with new one.

02 sensor

as you can see from this picture, both of my catalitic coverters are in good shape, now i know that its not the cats.
catalytic converter

I checked the EGR valve as is operational, according to the manual, i am soupposed to left up the diagfram and the engine should stall, and it did.

I replaced both PVC valves.

next: i wanted to do a fuel injection mysefl, but after reading how to do this, i need special expensive equipment, better just to take it to a shop to do this. I had to do a fuel injection cleaning on a toyota celica once in 1992 and they shop charged me $59 bucks. I bet this is going to cost me like $159 dollars now.. we'll see.. (i looked for a place to do the fuel injection cleaning but found none, so i didn't do this)

TWO WEEKS LATER ------------
I went back to the place where I failed t e emissions test the first time because they give a free retest. I was nervous taking the car back because I didn''t have to deal with taking the car to an auto shop for only for them to tell me its going to cost me like some $2,500 to fix it...

As I took the car back to the testing facility, I let the car idle for like 5 minutes before telling them to start the test, this way the catalytic converters will be hot thus burning the pollutions better. As the technician started to do the test, I prayed to Jesus for the car to pass the test. after about 7 minutes, I was relived when the guy at the emission test facility gave me a thumbs up. I remembered my prayer to jesus at that moment and thanked The Lord Jesus Christ.

at the end, I think my car failed because of the ba o2 sensor, you see, prior to taking my car for the test, I had replaced the engine with a JDM engine because the old one broke the timing belt and in the process it broke the whole engine.. Anyway, before I replaced the engine, my car had the check engine lamp (light) on with a o2 sensor code. When I removed the exhaust I found the passenger side o2 sensor was broken, the terminals were bent, so I thouhgt by straiting it it would fix it. After fixing the o2 sensor, the check enginee light went off so I thought it was fixed... Because I was cheap and not replacing it when I should have, I had to go through this ordeal.

its been about two weeks since i failed the smoge check and have done the following to prepare for the re-test:

* Changed the two rear Oxygen (o2) sensors
* Changed The Oil
* Changed Fuel Filter

I passed the test !!!!

Finally, I am so thankful that I don't have to deal with this for the next two years.

------ UPDATE July 10 2008 ---------

well, its been 2 years since i went trhough this whole ordeal. and yet again, when i went to the smog check station i fail.

i gave my car a tune up and still failed.

finally, i checked my computer for any errors, there was a p0325 error which is the knock sensor. i replaced it and then i passed the test on the third try

this is what the paper said:

Emissions Control Systems Visual Inspection/Functional Check Results
(Visual/Functional tests are used to assist in the identification of crankcase and cold start emissions which are not measured during the ASM test)
PassPCVN/AThermostatic Air ClearnerPassFuel Evaporative Controls
PassCatalytic Converter N/AAir Injection PassMIL/Check Engine Light
PassEGR Visual PassVacuum Lines to Sensors/Switches PassCarb./Fuel Injections
N/AEGR Functional   PassOther Emissions Related Components
N/AFuel Cap Functional N/AIngition Timing   
PassFuel Cap Visual PassWiring to Sensors PassOxygen Sensor
PassSpark Controls N/AFillpipe Restrictors PassLiquid Fuel Leaks
N/AFuel Evaporative Controls Functional     

1st Try - FAILED - on the first try i changed the sparkplugs, air filter, PVC valves - FAILED

%C02%02HC (PPM) CO (%) NO (PPM)
15 mph 169914.70.052910.490.020.0242457879FAIL
25 mph 189014.70.036710.460.030.02711501009FAIL

2nd Try - FAILED - on the second try i flushed the oil, changed the oil and oil filter, cleaned the intake with intake spray

%C02%02HC (PPM) CO (%) NO (PPM)
15 mph 174814.60.052980.490.020.0242457766FAIL
25 mph 187314.50.136780.460.030.0271150596PASS

3rd try -PASSED - i changed the two 02 Sensors and the knock sensor. i was getting a p0325 on the knock sensor so i replaced it, this time it passed the test. as you can see there is a big difference. the knock sensor is important because it affects the timing. so if your timing is incorrect, your engine can be running lean.. which means that its running more gasoline than air in the air/gas ratio. im not sure if the 02 sensors were necessary to change, but i didnt take any chances, they cost me about 75 dollars each, and the knock sensor was $189 dollars.

2008%C02%02HC (PPM) CO (%) NO (PPM)
15 mph 169914.70.052910.490.020.0242457106PASSED
25 mph 189014.70.036710.460.030.027115083PASSED

Aug 27, 2010%C02%02HC (PPM) CO (%) NO (PPM)
15 mph 170414.40.1529510.490.020.0642457133PASSED
25 mph 276914.50.1367240.460.030.0471150462PASSED

Why do you think you failed the test?