Smog Woes for 95 Nissan Maxima - Detailed
 

Hello

I hope someone has ideas on what the problem can be. My mods are MEVI,Ypipe, intake, and Greddy SP1 catback. I have a JWT ecu but removed it before the first smog test.

I have failed smog 4 times now and each time it is due to high nox. I have no clue on what it can be right now.

Before the second smog check, I changed the PCV and used Guarantee to Pass. I failed the 15mph test. I had the smog operator conduct a diagnosis and he stated that the EGR is working properly but is not opening all the way due to low backpressure from the catback. He stated that the catalytic converter was bad.

Before the third smog check, I had a new catalytic converter installed and it failed even worse on NOX. The new cat was universal and there does not seem to be any leaks.

Before the fourth smog check, I had the EGR tube and EGR valve cleaned, they were pretty dirty but it failed smog on the 25mph test and barely pass on the 15mph test.

There is a check engine code on now which just came on recently but the code is for the KS and the rear O2 sensor behind the cat. My obd2 reader shows the car going into close loop when I am driving and back into open loop when I am idling. I am assuming the top two o2 sensors are functioning properly.

Can the greddy catback cause a low back pressure environment where the EGR valve won't open all the way or is it a lazy valve? I have check all vacuum and there appears to be no leaks. So right now, I am at out of ideas. Any help will be appreciated.

Thanks.

Put your stock ypipe back on, change the cats o2 sensor and you should be golden.

Nox is the result of high compression chamber temps. How hot are you running? Lo backpressure could cause low EGR flow. Get a cheap exhaust tip and crimp it flat.

Car operating temperature appears to be fine. What are the normal ranges for chamber temps and how would i go about measuring it?

Don't know x2. Make sure your not too lean. Restrict your exhaust a little. And make sure your cooling system is right.

Not comletey closed off, just restricted.

Yeppers, high NOx is a result of high temps.

Maybe a good EGR cleaning would help clear out the lines. Or maybe running a little rich would cool things down. But then your hydrocarbons might go up.

I can't believe I'm already forgetting the exhaust basics I learned a few months ago. I think I'm getting old.

any updates?

Damn it in the same ucked up state for smog.....but isn't that bad where I go I pass NP bit now got a problem for the smog coming up...though...:D

I wanted to give a update. Car finally passed smog. I pour in Chevron synthetic techron in the fuel tank and seafoam the intake maniford and it passed!!! +1 for seafoam.

Did the KS ever code go away or is that still around?

Reason I ask is that I recall when I failed smog for high NOX and HCs the KS was bad so I replaced it and it passed. Even with an aftermarket Y pipe and a OEM type cat, I let the car idle for 15 mins before going into the smog check and it made it through.

No, the KS code and O2 sensor code is still around. I think the KS code is triggered by the O2 code and the O2 code came on right after my cat. converter was replaced.

did you ever pass?

Read post 10 members only jacket wearing manhandler!!!

Passed another smog test but after passing the test in 2011, I had it registered in a county which only requires sniffer and not the dyno which is way easier. I still barely pass this year. My HC was at 99 at idle and maximum allowed is 100. I been reading up on the TC-W3 additive and gonna try it on my ole Max.

Ole Maxima failed again due to high HC on the 2500 rpm test. It failed by 1 point. Fml.

Update, I was able to pass by using Seafoam in the brake booster and 2 cans in the gas. I need to remember to do that before each smog.

did it pass?

:buttkick:

Did it pass?

U gonna jinx yourself and your max won't pass smog.

Did it pass?

lmao

x2

:ban2:

I put the Maxima on non-op after the last update, it just sits on the street most of the time. Reminds me that I need to wash it and wax again. I still keep up on the maintenance of it but it's an extra vehicle at this time.

I dunno what the temperature is, it doesn't overheat. Car still runs great and I wouldn't hesitate to drive it across the Country. I have to keep this in mind if I decide to register it. Thanks for the advice.

I'm sure you are aware, but a non-op vehicle can't be parked on a public street. Be careful, a neighbor may report it to your local police department, and then PD will issue you a ticket.

I do know this and thank you for the warning.