Need some help. i have a aftermarket intake, y pipe and obx catback exhaust. i replaced the cat, spark plugs, pcv valve, 3 o2 sensors. Still failing. Anyone have any answers, will be greatly appreciated. 1995 nissan maxima

 

I suspect it has something to do with the EGR system.

Have you done the check on the EGR valve, ie. push up on it and see if there is movement. There should be.

Perhaps the EGR system requires a thorough cleaning.

 

did you replace the cat with an aftermarket cat or stock ? ive heard of people failing the sniff test using aftermarket cats

 

If your HC and CO readings are within spec, then it is most likely your EGR which is solely responsible for reducing NOx emissions. As someone else said, check for operation of the valve and also give the system a good cleaning.

 

I just had a similar problem. In Ontario the limit was 430 and I read 1200 for NOx. I had a brand new full performance exhaust system on with a high flow cat. I know some people that have passed no problem with that combo but they are generally 97+. The 95-96's seem to act differently. Anyway, I threw on a stock Ypipe and stock old cat and the NOx went from 1200 to 10 or so. Massive reduction! Forget the EGR cleaning - I did that before swapping exhausts and I went from 1200 to 1190 - unless yours is completely plugged.

 

I really think you just happened to be experiencing an intermitten problem with your egr, cat does nothing for NOx.

 

I am assuming Maxima's use standard three way cats which has a lot to do with NOx readings. A TWC reduces oxides of nitrogen to simple nitrogen (N2) and carbon dioxide. TWC's are coated on the inside with a few substances. One being rhodium which is a reducing catalyst for NOx. So saying a cat does nothing for NOx is very wrong.

If you want to go the EGR route first, check it for function but make sure you also clean the EGR guide tube. It usually clogs up before the actual EGR valve fails.

 

I failed emissions also but for the other two HC and CO. I wanted to know how to pass because my tags are expired and I don't need a ticket. I replaced the MAF about 9 months ago so I don't think it that. I heard Seafoam in the oil case and fuel tank will make a quick solution to pass. Is this true? And any recommendations on where to start fixing the problem.

 

You are correct and have owned me. However the original poster has a new replacement cat in place and is still having issues.

 

emissions is easy to pass this may sound stupid but get a whole bunch of paper towel and stick in your exhaust. Dont worry about how it sounds once it idles and stays on with a good amount not to blow out then you will pass inspection. Stick it in there good so its not too visible. Works for me every time... believe it or not......

 

Trey 7467 - Failing on HC - the initial thoughts are always the O2 sensors being faulty and the car running rich as a result. Check them.

mbb6 - what kind of cat did you replace your stock one with?

Streetracer95gx - A better avenue might be to actually have a good running car IMO. That sounds like a fire waiting to happen?

 

well... you got to do what you got to do and im pretty sure they fire extinguishers were you go to have it inspected.

 

Does an O2 sensor throw the check engine light because mine is not on. My car's exhaust rattles and shakes like crazy during idle and even while driving. And the first time I start it it takes a few cranks before it starts. I will change both O2 sensors. See what happens. Thanks for the advice and any other advice for the other problems would be appreciated.

 

Many times a faulty O2 sensor will not trip a CEL. I believe the CEL is only tripped if the O2 sends a certain voltage. However, long before that the O2 can be working improperly but not send the right voltage signal to trip the light. My advice there is to definately get a scanner before you go shelling out some considerable dollars for 2 oxygen sensors.

The rattle and shake are probably the cat heat shield - no big deal but annoying. Of course it could be something else as well....

So check the O2's with a scanner, run a bottle of fuel injector cleaner too, and change the plugs if you have yet too.

 

So I replaced my spark plugs, both of the O2 sensors and the rear bank ignition coils. I passed the HC and CO emissions but now I failed the NOx emission which I originally passed the first time when I failed the HC and CO. Now I have no idea where to start repairs. Is there a how to for the EGR system?

 

Run your car down to apprx 5gal of gas left in tank (less than 1/4).
Put in 1 gallon of DENATURED ALCOHOL - $15. at lowes or home depot.
It will absolutely work and wont hurt your engine, Just fill up after your done.
It burns so clean you'll be amazed.
(the only time it wont work is if your burning alot of oil).

 

Wtf??????? ^^^^^

 

I could be mistaken but how is denatured alcohol going to help NOx? I can see it helping HC for sure.

Trey - what cat did you buy as a replacement?