# 1990 Max SE Didn't Pass Emissions!



## fugiot (Jun 27, 2003)

Ok, got a 1990 Maxima SE that passed emissions in '02 with a C0 reading of 6.8 or something like that. The limit in Colorado is 20.000. But just a few months ago when I tried again, I got a 23.xxx. So I failed by a little bit. Here's the thing, new injectors, new fuel filter, new air filter, new MAF, new distributor cap and rotor, new NGK plugs, no CEL, no misfiring and somehow it's still running a bit rich. I can't figure out why. Pretty sure it's not the o2 sensor, but would that be a culprit? And how could I find out before I spend $90 on a new one? Also could it be the PCV valve?


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## old90 (Jan 18, 2005)

Just off the top of my head I think the O2 sensor is the only thing left (not 100%). Did you do the work yourself? I did my injectors on my 90 MAX in January and replaced some of the old vacuum hoses in the process. I just found one that was a little too large and was sucking a lot of air. So if you did the work yourself check for vacuum leaks. 

Maybe someone can post on how to use a diagnostic computer to see what the computer thinks is wrong. 

old90


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## fugiot (Jun 27, 2003)

No, I didn't do the injectors myself. So hopefully they did that all correctly. Maybe it IS the o2 sensor...wish I knew for sure.


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## Matt93SE (Sep 17, 2003)

do you know how to pur your ECU in diagnostic mode?

let the engine warm up for about 15 minutes and shut it off. then pull the right panel off your center console.. you'll see a screw on the side of the ECU.
turn it fully clockwise and back, then start the car.

the CEL should be blinking somewhat random. the CEL is tied directly to the O2 sensor output.. if it's working properly, it will usually run rich when you're flooring it to rev the engine, then will run lean when you let off the gas..while the car is idling, it should flash on and off about once or twice every second as the ECU is constantly adjusting the fuel mix...

If you see that, then your O2 is working. If you don't see that, then it's dead.

easiest way to check right there.


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## fugiot (Jun 27, 2003)

wow, that's awesome! I'll do that. You sure know your Maxes


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## Matt93SE (Sep 17, 2003)

I've broken a lot of stuff in the 7 years I've owned a 3rd gen.


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