Tip & How-To about Chevrolet 1500

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.

Posted by on

Cars & Trucks Logo

Related Topics:

Related Questions:

1 Answer

How fix that problem


fix-problem-eyuevxexiacaa0vc32pfdm3j-5-0.jpg
Nitrous Oxide NO is created when an engine's combustion chamber temperature reaches over 2500F. 1. Lean Fuel Mixture - Lean fuel mixtures cause high NOx. A lean fuel mixture exists when less fuel then required is delivered to the combustion chambers or when more air then necessary is added to the fuel. In either case the lack of gasoline needed to cool the combustion chambers down is not present. Combustion temperatures increase causing high nitrous oxide emissions. A lean fuel condition may be due to a vacuum leak/s and/or defective fuel control components, such as the Air Flow Meter, Engine Coolant Temperature Sensor, and O2 sensors.
2. Defective EGR System - The Exhaust Gas Recirculation system is designed to reduce NO. The EGR system consists of an EGR valve, EGR pressure sensor, vacuum hoses, and one or more vacuum switching valves or solenoids. newer vehicles may use an electronically controlled EGR valves, which do not require vacuum lines or switching solenoids.
The EGR system's job is to re-route a small amount of exhaust gas back into the intake manifold to help reduce combustion chamber temperatures. As mentioned above NOx is created when combustion chamber temperatures reach above 2500F.
By recirculating exhaust gas back into the intake, a small amount of the air/fuel mixture is replaced with inert gas, reducing combustion temperatures.
3. Defective Catalytic Converter Some vehicles operate without EGR valves. Non-EGR equipped vehicles rely heavily on the Catalytic Converter to assist in the reduction of NO. These vehicles have tendencies to develop CAT problems sooner then those which are equipped. If you own a non-EGR equipped vehicle, and have failed the emissions test for high NOx, pay close attention to the Catalytic Converter.
4. High Engine Mileage - Over an engine's lifetime, carbon build-up develops in the engine's combustion chambers. The more miles on your engine, the more carbon build-up on the pistons, cylinder heads and valves. Carbon build-up decreases the available space for the air/fuel mixture to combust, and causes higher cylinder compression. High compression results in high temperatures and high NOx. Keep in mind this problem is usually seen in vehicles with over 150,000 miles which have been poorly maintained. The solution to this problem is called De-Carbonizing. It will remove a good amount of carbon out of an engine. This will increase combustion space, lower compression and lower NOx.
5. Engine Overheating - Inadequate engine cooling can will high NOx. If your vehicle's cooling system is not working efficiently, high NOx will be created. Remember high NOx nitrous oxide is created when an engine's combustion chamber temperatures reach over 2500F. You will want to make sure your vehicle's cooling system is working properly, and your vehicle's temperature gauge is always indicating normal.

Carbon Monoxide is a by-product of incomplete combustion. Carbon Monoxide exceeding maximum limits, can be due to a number of emission failures ranging from inadequate air intake to defective engine computer sensors. This condition is referred to as a "Rich Fuel Conditon".
1. Dirty Air Filter - The number one overlooked emissions component, yes, "emissions" component is the engine air filter. A dirty air filter will absolutely restrict air flow, thus disturbing the proper 14.7:1 air/fuel ratio required for optimum fuel combustion.
2. Faulty Oxygen Sensor The Oxygen Sensor is responsibly for delivering information to the ECU or ECM relating to the oxygen content in the exhaust stream after it has left the combustion chambers.
The engine control computer will determine how much fuel to inject into the combustion chambers based on this data. The more oxygen in the stream, the more fuel the computer will deliver, and visa-versa. A defective O2 sensor will cause increased carbon monoxide emissions.
3. Defective Manifold Absolute Pressure - The MAP sensor determines the level of vacuum created during an engine's intake stroke, and sends this information to the ECU. During low vacuum the MAP sensor assumes the engine's throttle is in some degree open, meaning you've stepped on the pedal. It relays this information to the ECU. The ECU, in turn, sends commands to the fuel injectors, or carburetor, to increase fuel delivery.
A defective MAP sensor will not report the correct information to the ECU, thus disturbing air/fuel ratio. Usually when the ECU senses a defective MAP sensor it will learn to ignore its data, and rely on preset values, and other sensors such as the Throttle Position Sensor, and Engine Coolant Temperature Sensor; Fuel delivery will not be as accurate and high CO may result.
4.Defective Throttle Position Sensor - Obviously a very important emissions sensor; the TPS relays information regarding the position of the air intake system's throttle plate. The throttle plate, located after the engine air filter and before the intake manifold controls the amount of air entering the combustion chambers. It is usually manipulated by the gas pedal via a cable. On late model vehicles the throttle plate may be controlled electronically. A defective throttle position sensor will confuse the ECU into thinking the vehicle's operator is demanding more or less fuel, when neither is really neccessary. Most often a faulty TPS will cause high CO, as an engine's ECU always prefers to send more fuel rather then less, in an effort to avoid a lean fuel mixture and subsequently higher engine temperatures.5. Defective Engine Coolant Temperature Sensor - Low engine temperature requires more fuel. When the ECU is unable to determine what the engine's accurate temperature is, it will not adjust fuel delivery properly; resulting in high CO. As explained above, the Engine Control Computer prefers to send more fuel rather then less to avoid a lean fuel mixture.

Hydrocarbon HC. Hydrocarbons are basically raw fuel, otherwise known as Gasoline. High Hydrocarbon (HC) emissions are almost always a sign of poor fuel ignition. However, it's not always that the engine's ignition system is responsible for high Hydrocarbon emissions.1. Improper Ignition Timing - Engine ignition timing is measured in degrees before or after Top Dead Center. Example of an ignition timing failure would be in the case where an engine's ignition timing is required to be set at 10 degrees Before Top Dead Center and instead is set to 15 degrees BTDC. This fault will not only cause a smog check "functional failure", but will increase Hyrdocarbon (HC) emissions as well. California allows 3 degrees +/- off of the manufacturer's required setting. Newer vehicle's may not have a distributor, and and no timing adjustment will be needed. On these engines timing is electronically controlled by the ECU.
2. Defective Ignition Components Your vehicle's ignition system consists of the ignition coil/s, distributor, distributor cap, distributor rotor, ignition wires, and spark plugs. If any of these components are defective the engine will produce high hydrocarbons. A common reason ignition components perform poorly is due to carbon build-up. High ignition voltage traveling through the air pockets within these components form carbon. Carbon acts as an insulator between paths of electricity, decreasing the energy required at the spark plug to ignite the air/fuel in the combustion chambers properly.
3. Lean Fuel Mixture - Any condition which will cause unmetered air to enter the intake manifold, and ultimately the combustion chambers, will cause high hydrocarbons (HC). This condition is called a lean miss-fire. Such faults as vacuum leaks and gasket leaks will cause lean fuel/air mixtures. Broken, disconnected or misrouted vacuum hoses will do the same. It is also important to note that many engine components rely on engine vacuum for proper operation. If any of these components are defective, externally or internally, they may cause large vacuum leaks as well.
4. Defective Catalytic Converter - A defective catalytic converter may be responsible for high HC, CO, and NOx emissions. The Catalytic Converter, commonly referred to as the CAT is a component designed to continue the combustion process within itself and emit a more thoroughly burned and less harmful emissions containing exhaust. The most accurate way to find out if your vehicle's CAT is working efficiently is by using an exhaust gas analyzer. Unfortunately this tool is fairly expensive.
Some obvious symptoms of a bad CAT could be any of the following:
a. Major loss of power over 15-25 mph. This may be an indication that the catalytic converter is plugged up and restricting exhaust flow.
b. Strong sulfer or rotten egg smell emitting from the exhaust on an otherwise good running vehicle. This may be an indication that the Catalytic Converter isn't burning fuel completely, instead storing it, then releasing it as hydrogen sulfide.
c. Loud rattle being heard from inside the CAT. This may indicate a broken Catalytic Converter substrate. You may want to insure this sound is not due to loose exhaust components.
5. Defective Air Injection Components - Faulty smog pump and related emissions system components will cause high HC. The air injection system is designed to introduce additional oxygen, after the metering system, to the engine exhaust as it exits the exhaust manifold, or directly before it enters the Catalytic Converter; thus burning whatever remaining fuel (HC) in the exhaust completely.
6. Low Cylinder Compression - This fault is one of the less common high HC causing problems. Reasons an engine may have low or no compression in one or more of its cylinders may include things such as burned intake or exhaust valve/s, defective valve guides and/or seals, defective piston rings, and burned head gasket/s. A wet/dry cylinder compression test will diagnose this fault. More then often if such a problem exists it will be very apparent. You should notice rough idle.

Feb 19, 2015 | Cars & Trucks

2 Answers

what is the egr system


EGR stands for Exhaust gas recirculating system

Apr 07, 2012 | Cars & Trucks

1 Answer

what is the meaning of a failing test with NOx(ppm)


Oxides Of Nitrogen (NOX)

Above 2500 degree engine combustion temperature
nitrogen bonds to oxygen to form NOX

The EGR Valve is supposed to allow a certain
amount of exhaust gases into incoming air to
control high combustion temperature and control
NOX

Bad Egr Valve
Engine operating too hot
Cat too cool at inspection station
Fuel mixture issues
PCV issues
O2 Sensor issues
Injector issues
Ignition issues

Jan 30, 2011 | Toyota Previa Cars & Trucks

1 Answer

Keep failing emissions test due to high no levels. I have replaced the oxygen sensor and do not know what could be causing this problem.


NOX is created when the engine's internal combustion temperature gets to high.In addition to maintaining proper coolant levels.The egr system may be malfunctioning.The egr valve uses spent exhaust gases to line the cylinders walls reducing internal combustion temperature and reducing the amount of NOX produced.

Jun 18, 2010 | Cars & Trucks

1 Answer

high nox fail smog test any remedies? 99


NOX is created when the internal combustion temperature gets to high.The egr system uses burnt exhaust gases to line to cylinder walls.The purpose of this is decrease internal combustion temperature therefore reducing the amount of NOX created.Would look to a possible egr malfunction usually they will trigger the check engine light but not always.The 4.3L has been known to have issues with carbon buil up in the egr and the egr pintle not open and closing properly.

Jun 07, 2010 | 1999 Chevrolet Astro

Not finding what you are looking for?

1,074 people viewed this tip

Ask a Question

Usually answered in minutes!

Top Chevrolet Experts

yadayada
yadayada

Level 3 Expert

75744 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22114 Answers

Jeff Turcotte
Jeff Turcotte

Level 3 Expert

8123 Answers

Are you a Chevrolet Expert? Answer questions, earn points and help others

Answer questions

Loading...