# 1994 Nissan Sentra Failed Smog, Help Needed



## Yody (May 9, 2012)

Hi, I just bought a 94 Nissan Sentra with a 1.6L. It failed california smog with high HC at 15mph. As well the CO was kinda high, and the NO very low.

It looks like the previous owner just recently did a spark plug wires, plugs, fuel filter, possibly a new Nissan MAF, Air Filter, and O2 Sensor.

I do have a slight tensioner rattle but I'm not sure if that is affecting smog at all. I haven't checked the timing myself but the tech has it at 10BTDC.

I'm thinking its running rich due to something, maybe timing, fuel injectors? I'm thinking thats maybe why the NO is low, because its running rich, making the mixture cooler.

I'm pretty mechanically efficient and am ready to tackle this. Just not sure what problems are inherent to Nissans and where to start looking first.

THANKS


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## Yody (May 9, 2012)

Oh and it is a five speed and has 127K on it. Catalytic Converter look stock. Car runs and drives pretty much perfect.


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## i r teh noobz (Apr 26, 2007)

Rich sounds right to me. The 02 is zero and the CO is a bit high (according to you, I can't seem to find my charts from school top confirm. We don't have emissions tests here, so I'm a bit rusty on the numbers). Sounds like a lack of oxygen, so rich. Lack of oxygen could also cause low NOx, as they require oxygen to form.

The fact that it barely passed HC at the higher RPM suggests a consistent issue, like a leaky injector or something. Perhaps there is an issue with the coolant temp sensor telling the ECM that its cold out? I think there are separate sensors for the ECM and temp gauge, but I'm not 100%. Its been years since I owned a Sentra.


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## OneCarAfterAnother (Mar 4, 2011)

I agree the guy above me ;] youre running a little rich in idle. Its not the cat so dont replace it. Check your o2 sensor - the easiest check. Check your Coolant temp sensor to make sure it is good. For some reason my car runs with 0 on o2. And your running so low on Nox because youre rich :]


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