So, my Maxima *just* missed passing emissions last time. MD tests 3 things, NOx, CO, and HC. HC it passed but NOx and CO it was just out of spec on. I don't have the specific numbers here, but I could get them if it would be helpful. Any suggestions about what I can do to help the car pass? I am already planning to install a new O2 sensor (car probably needs it anyway), and the car had a new pre-cat and cat about 2 years ago. AFAIK they are still good. I've heard that a little alcohol in the gas tank will help. Any truth to it? Any other tricks like that? Like I said, it was close so just a little "bump" would probably do it.

TIA

I was my experience that the alcohol helped reduce HC, but that was on an old carbureted car. With fuel injection, the system seems to compensate and add more fuel to compensate for the oxygen in the alcohol. Usually an oil/filter change, fresh air filter and new plugs are all it takes on my older cars. How well does it run? Any blow by issues? Are the cap, rotor and wires in good shape (assuming it has a distributer)? Have you cleaned the throttle body air horn? The O2 sensors are probably a good idea.

If you retard your ignition timing it will reduce NOx, but your HC's may start to come up. Alcohol is mainly for HC's, but will help Nox a little.

Where you sitting in line for a long time? If so you may need to go through at a non busy time so the cat can stay hot. I had an 88 Ford Ranger that I disabled the EGR on (got about 3 mpg better) and I ran the thing hard up and down the road around the emissions inpection station to get the cat real hot, then went through. Passed prefectly.

EGR helps with NOx is yours working?

No idea if EGR is working. I wasn't in line very long, but I went through lane 1 and I've never passed when I've gone in that lane. I think I'll try a different lane next time.

The throttle body is a problem on this car, has idle issues that I think are related to it. From the graph, the car seems to have normal emissions when the car is moving, but they jump a little when the car is decelerating or sitting still. I don't want to mess with timing, I'm fairly sure the HC would jump too much. It wasn't that low.

I also have put new tires on it that seem to be about .5" larger, maybe this will help? ALso, I had old oil in it, but they say that only affects HC. Oil has been changed since.

I have a friend who is really into Ni$$ans. They are cheaper by the dozen. :-)

IIRC, the EGRs are problemmatic, and a pita to replace. You have to pull the intake. With age, they will frequently have issues with vacuum lines, especially the ratsnest that goes under the intake. Make sure all the ones you can see and get to are good. The comments Mike had were good. Here is what I usually do on a car that is about to undergo its first emissions test:

plugs, wires, cap, rotor. You will be amazed what a difference wires can make, even factory replacements.
O2 sensors, especially if the ones on the car are more than a year old. Spend a little time on the Nissan lists, or ask someone who knows Nissans on what the best brand for those cars are. Some have to have factory parts, some are okay with aftermarket.
fuel filter, air filter.
If the thing uses a vane air meter, make sure the door operates properly.
If the thing uses a MAF, use a MAF cleaner on it, especially if you are using a K&N type air filter (one of those with oil on the media).
verify the TPS is properly adjusted and clean.
change the oil and filter just before going for the inspection. If you fail and have to go back, change the oil again.
Make sure the car is good and warm before going in. Drive on the freeway for 10 minutes, or so before stopping in, to make sure the cats are as hot and clean as they can be.

If it still doesn't pass, there is an additive called 'Guaranteed to pass emissions', or something like that, by CRC you can try. I haven't tried it yet, but it may work. Other than that, you are probably looking at replacing the EGR, CATs, or both, as well as looking for vacuum leaks and failing switches/ported vacuum valves.

Good luck!

Had you changed the oil recently? Remember how much the #'s dropped on the old A.I. van when we changed the oil. Granted, nobody could remember when/if the oil was last changed in 10 years of club ownership.

I tried one of those "guarantee to pass" bottles from Advanced Pep Zone in my Firebird a few years ago. Didn't affect the #'s one bit.

In my Nissan, the EGR is right on top of the intake manifold so it's pretty easy to check. I took it off my old raSEcaR and it was pretty gunked up.

Otherwise, plugs, wires, dist cap/rotor, O2, PCV, clean TB, etc.

Pat

I'm no expert on Nissans by any stretch of the imagination, but I am pretty sure on the Maxima, it is under the intake. It may be different for the different gens, but I do remember my friend parking a 4th gen Maxima because the EGR light was on, and he didn't have time to pull the intake manifold.

Gene Beaird