I failed smog test last week, I have since got a new cat and EGR valve installed and I failed again tonight. I changed my O2 sensors last year, but I'm not sure if I got the right ones. (Ive read somewhere that there is only one brand to stick with) I installed Bosch p/n 15703, I am thinking now that they could be the cause of it running lean leading to the high NOX readings. I am getting between 1050 and 118 at 15mph and between 1111 and 1269 at 25 mph. Other readings are below average. Do you guys think I might need o2 sensors again?

 

What kind of coolant temps are you seeing?

 

Coolant temps are steady right in the middle of the gauge.

 

whats the fuel pressure, did you ever have the pcm tuned, if so they might have advanced timing? do you have any idea of the actual temp numbers? the gauge cane be misleading. are the inspectors using the fan while running the test. high NOX numbers indicate to high of a combustion temprature. usually this is combated under part throttle by the egr system introducing exhast gas into the cylinders. egr solenoid could be bad, can you verify that the egr system works? high combustin temps may also be caused by a lean condition, your mods may cause this and the pcm would need to be tuned to correct it. a mail order may not be sufficent to get it to pass the sniff test. do you have any way to read long term fuel trim? this will tell you if its running lean. i hate the sniff test it is much harder to fool than the obd2 test. good luck

 

I know the guy wasnt using the fan, and he was lugging the engine in third gear at 25 mph. I asked him if he could check it in second gear at 25 mph and he said he couldnt. I dont know why, I think he wants me to bring it to him so he can fix it, since he just opened up a repair facility next to his test only station.

 

i have seen cars fail on nox due to the test facility not using the fan. he probably could not test in second gear due to the rpm range standard. but a luging engine will also cause high nox. i dont know how much the inspection is in cali but you might try a different station and make shure they use the fan. also keep an eye on the rpm range on the screen to see if they can use second gear. i know in texas it will give you two trys per test to pass.

 

Did you test your new EGR valve to see if it is working? If so, then maybe your EGR solenoid isn't opening your EGR valve.

Can you view your current data to see if the O2s are switching high and low?

 

Well, I'm going for retest on Tuesday, I got my new delco o2 sensors in tonight, gonna make sure he uses the fan. My EGR valve is functioning properly according to my scanner

 

You scanner will only tell you what duty cycle the PCM is commanding. There is no feedback to verify that the EGR valve is performing the way the PCM wants it to. The OBD-I EGR flow diagnostic is not very sensitive, so its possible to have an EGR valve that isn't moving, and not get a code for it.

 

What about jumping the EGR Solenoid to see if the solenoid is operational? If there is no change, then the solenoid may be bad which cannot send vacuum to the EGR Valve.

Also, holes or corroded rubber hoses should be replaced. Silicone hoses preferred.

 

you can verify the flow of the egr valve by conecting a hand held vacum pump directly to the egr valve. with the engine running apply about 10 - 15 inches directly to the vave, the engine shold stall or come vey close. without a scan tool that will comand egr flow you can verify egr solenid function by hooking up a mechanical vacum gauge to the egr solenoid with a alog pice of vacum hose and go drive the car and watch for it to register vacum when your scan tool indicates the pcm requests egr flow.