Question about 1997 Nissan Maxima

1 Answer

HC & CO% emission

I have Nissan Altima 94, GXE, and it has been faiked for HC and CO%. I have changed spark plug and distributor cap, roter and still did not passed. Please advise? Is the Oxygen Sensor needs to be replaced?

You help will be greatly appreciated.

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  • prabhatk8 Apr 19, 2009

    I am very sorry Guru for not providing number,
    The numbers are

    HC -Standard 100 and Reading 297

    CO%- Standard 0.50 and 0.52

    It has 187k mileages and I am using Castrol 75000 high mileage oil.

    You so helpful in my present situation.

    Thanks alot.



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  • Nissan Master
  • 383 Answers

Prabhatk8: I am going to run several things by you, OK?
1. If the oil and filter have not recently been changed, it is possible that the high readings are a result of what has collected in the crank case and is being drawn up through the PCV. The contamination is enough to fail the emissions. You did not mention the numbers, so I can only offer suggestions, starting with the simplest solutions and continuing on with more complex solutions.
2. The Ignition timing being advanced can cause the condition you have described, to a certain degree. However, the HC readings, are these being taken at an idle and at above 2,200 RPM ?
3. Nissan also dated their plug wires. If you look at the wires closely, the outer insulation should have the year the wires were manufactured. The insulation is marked about every 6 inches or so. Old wires can cause agrivate a problem like you have.
If the car has the factory wires, they will either have the name "Yazaki" or "Sumitomo" on the wire insulation. These are excellent quality wires! If you decide to replace them, either replace them with the factory (dealer supplied) wires or ones made by NGK.
I have found nothing equal to them in performance and longevity.
Don't go cheap on the ignition parts! Too much of an air gap between the cap and rotor will raise the HC level. Excessive gap on spark plugs or weak spark will also create the condition.
The oxygen sensor can cause the problem, however, don't just replace it because you suspect it may be bad. The part can be tested, but you may not be equipped to do so. Check with Auto Zone or O'Reilley's. They have scanners. Some of these scanners have the ability to monitor the Oxygen sensors in "Real time". Which means looking at them functioning while you are standing there. The sensor is actually a voltage generator which generates milli volts based off of the exhaust passing over it. The more or less oxygen that is present in the exhaust, changes the voltage values which in turn is sent to the ECM to adjust the pulse width of the injectors , keeping the CO and HC within certain parameters.
Technically they refer to it as a "Lamda Window".
(Lamda, Lambda, Lambda and Omega Moo!)( I couldn't resist! For those of you who saw the movie the Revenge of the Nerds)
Sorry...where was I.?.........
4, A false air problem can cause this symptom depending on where the leak is. Check for a small crack or leak in the boot which connects the air mass sensor with the throttle body.
5. The Altima's among other Nissan's had problems with condensation dripping down on top of the ECM's connectors where they plug into the ECM. When they got corroded, this would affect the performance , including EMISSIONS.
PK, I hope this will give you some direction to go in. If the numbers are "real close" In all likely hood, if you change the oil and filter just before you go for the test, you will probably pass.
Tell me what the numbers are, including th e "NOX" figures.
I I know what these are, I can help you more easily. What I am doing here is shooting in the dark!
Good luck and let me know if I have done you any good.
P.S. If you un-plug the connectors at the ECM and they are corroded, there are cleaners you can buy from Radio Shack and the local automotive parts houses. One is for cleaning and neutralizing the corrosion and the other is a dialectic grease which you apply to the connectors afterword's to keep corrosion from coming back.

Posted on Apr 18, 2009

  • Bill Hackett Apr 19, 2009

    pk: your numbers are not too far off. When you had gone for the exhaust testing, how long had it been since you had had and oil and filter change?

    Was the test done at an idle only or do they test at idle and at roughly 2200 RPM ?

    Also, depending on who is doing the testing, there is what is called a "preconditioning" period where the engine is run for a certain period of time at higher RPM's prior to testing. The reason being that the catalytic converter must be hot prior to testing or you WILL get higher emissions readings such as what you have described. That is the job of the catalytic converter.

    I have found on some cars, I have even had to take them out for a short hard run to get them hot prior to testing, when the vehicle has gotten the mileage yours has on it. I will spend a little more time for my customers in in testing their cars or preconditioning them prior to running an exhaust analysis because it may take a little more to precondition it than it did when it was new. If the oxygen sensor was bad, usually it would cause the check engine light to come on.

    In any case, I have given you quite a bit to go on and in all likelihood, I am going to guess that you answer is within what I have supplied you.

    Good luck and let me know how things work out...

    P.S. You might even stop at a few other shops that do emissions testing an see if you shop was testing you car in the same manner as they were. Testing should be uniform anywhere you go in the country.


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