Question about 1994 Mitsubishi Galant

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Emissions failing with high NOx

Took my mitsubishi through CT emissions 4 times and failed everytime on nox only, my numbers dropped a little everytime with repairs until i put the new egr valve on then my numbers shot up higher then they were in the first place and now i'm not sure what to do. new plugs new wires distributor and cap and router tryed the gas additives air filter evap canister cant afford a new cat so any help would be greatly appreciated.

Test One HC 103 CO 0.37 NOx 1891

basic tune up plugs wires air filter distributer cap, router then took
Test Two HC 91 CO 0.40 NOx 1876

tried the gas additives heet fuel injector cleaning etc.. then took
Test Three HC 96 CO 0.43 NOx 1761

replaced egr valve then took
Test Four HC 97 CO 0.42 NOx 1965

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  • kim51581 May 21, 2009

    Was told that the sensor was not bad or I would have failed on the co and hc as well.. I only failed the NOx

  • Anonymous Mar 25, 2014

    co emissions too high for mot



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You need to check the oxygen sensor. You car may be running lean and therefore giving you increased NOx levels

Posted on May 30, 2009

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Change the lambda/oxygen sensor in the exhaust.

Posted on May 21, 2009

  • haydnm0 May 21, 2009

    The only other thing to bear in mind is that because your car is later than1991 the it is fitted with a three way catalytic converter, this monitorsall three gases and one can be affected without throwing all three out.
    By the sound of the list of work that has either been checked or changed I would be looking at the Cat.
    Has your head gasket gone and been fixed in the past year as this can cause the NOx to be higher than the rest, due to the antifreeze getting into the exhaust system and causing long term damage, just a thought.
    Hope it helps and goodluck.



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Failing emissions testing due to high NOX (oxides of nitrogen)

I have seen several people posting emissions failures due to high NOX (oxides of nitrogen). Nox is created when the engine's internal combustion temperature gets to high.

Two reasons this can occur is improper coolant levels and a malfunctioning egr system. The egr system injects exhaust gas from the exhaust and uses it to line the cylinder walls.This in turn reduces the combustion chamber size and internal combustion temperatures. Ultimately this reduces the amount of NOX created. These systems functioning properly can be the difference in passing or failing your emissions testing because of high NOX ppm.

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Thousands of technicians have faced the challenge of bringing a particularly stubborn application into compliance for NOx emissions. High NOx readings are a clear sign of performance issues somewhere in the system. The question is, where?
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