High NO Level During Emissions Test

Check out the videos. Also drop a bottle of Fuel System Cleaner to a quarter tank of gas.

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CO? That means Carbon Monoxide - it's a rather toxic and poisonous gas emitted from the exhaust system.

When they check emissions on cars CO is one of the gases they measure. If the level is too high .. your car fails the emissions test. I believe in the USA the emissions test is known as the 'smog test'?

If you have a problem with excess CO emissions on a car the cause is often an incorrect fuel/air mixture or a faulty sensor called the lambda/oxygen sensor in the exhaust system

Can you remember how many miles you have driven since the engine was installed? What I mean is that if you have a good running engine and have a new converter, sometimes the easiest things are the ones overlooked. Check your air filter to make sure it isn't dirty and restricting air flow. Also check your spark plugs to see what kind of shape they are in and if they are burning clean. Spark plugs can tell a lot. If you had transfered any emission related parts from the old engine to the new, maybe one of those items has an issue or is clogged. I hope this helps. Good luck.

Have you tried Engine decarbonizing type foam to remove the excess carbon for the engine?

It does have an EGR valve

You engine came with EGR, here is a picture of it, make sure it is functional.

Your EGR is plug or is non operational,When the EGR is not plug and is in operational its job is to cool the combustion chamber thus lowering Nox.

run the fault codes to find the faulty sensor
sensors that control the exhaust emissions are the HO2S ( heated oxygen sensors in the exhaust manifold/s
the O2 sensor ( oxygen sensors after the cat converters ) and the EGR unit that recycles exhaust gas back through the engine to re-burn the gasses

change the oil just prior to test, run the engine at very high idle just prior to test to super heat Catalytic converter, this will lower reading as much as 100 PPM.

Do an oil change with 20W50 oil (or one grade higher) to prevent blow by during the test.

You current oil has HC from blow by though the rings.

Do a fresh oil change will lower the HC.

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Change spark plugs,wires,cap and rotor if they are over 24,000 miles
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Make the smog check appointment for the EARLY MORNING. Colder air will help the fuel burn better.

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Clean or change the air filter and pcv valve.

Clean Mass Air Flow sensor with CRC Mass Air flow cleaner or electronic part cleaner.

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Do a quick wipe down on the wires and cap to take the moisture off.

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Check spark plug wire contacts for corrosion.

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Fill the tank to around 3/4.......just in case your fuel pump is weak.

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Ran the truck for 20+ minutes on highway before the test.

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Do not carry excessive cargo on the truck bed.


These are the little things I would do to get the HC and CO down.


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