EGR valve operation

EGR valve operation

What is an EGR valve and why does an engine need it?

An EGR valve is used on engines to reduce the formation of oxides of Nitrogen (NOx), a key component of smog. NOx causes respiratory issues and is an eye irritant, so reducing it offers critical health benefits to the population.

How NOx is formed

The air we breathe contains approximately 80% nitrogen, so 80% of the air entering your engine is nitrogen. NOx is formed during the combustion phase when oxygen and nitrogen combine at high temperatures (2498°F). The best way to reduce NOx formation is to reduce combustion temperatures.

One way to do that is to dilute the air/fuel mixture with inert exhaust gas during the intake stroke. Since the piston pulls in a pre-determined volume of air/fuel during each intake stroke, adding some non-burnable exhaust gas reduces the amount of air and fuel needed to fill the combustion chamber. Less air means there’s less oxygen entering the cylinder. Less oxygen and less fuel lowers the combustion temperatures by about 300°F. That’s enough of a difference to dramatically reduce NOx formation.

Obviously, the engine produces less power if it’s being fed less air and fuel, so the EGR is only active during low power demand periods like during idle and low speeds. For example, the EGR valve can be up to 90% open at idle. However, as more torque and power are required the EGR valve closes to ensure as much oxygen enters the cylinder.

An EGR valve can be used in smaller GDI engines to reduce pumping losses and improve both combustion efficiency and knock tolerance. In a diesel engine, EGR can reduce diesel knock at idle.

What is an EGR valve?

The EGR valve is responsible for metering exhaust gas into the intake manifold. The valve can be commanded full closed, full open or any variation in-between.

Older style EGR valves were vacuum-operated, but modern valves are electronically controlled. EGR valves also contain a position sensor that reports the actual opening to the PCM so it can compare the commanded opening to the actual opening. If there’s a discrepancy between commanded and actual, the PCM will set a P0404 EGR circuit range/performance.

Diesel EGR valve

Diesel engines produce far more soot than gasoline engines. So modern diesel vehicles employ a diesel particulate filtration system to remove the soot. If the soot-laden exhaust is routed directly into the combustion chamber, it can mix with oil vapor and form sludge. To prevent that, a high-pressure EGR valve is used to divert the high-flow, high-soot exhaust gas to the diesel particulate filter first before it enters the combustion chamber. The filtered exhaust gas is then passed back to the inlet manifold either via a pipe or internal drillings in the cylinder head.  A secondary valve is also used to help create a vacuum in the inlet manifold as this is not naturally present on diesel engines.

What is an EGR delete

Powersports enthusiasts often remove the EGR valve and cover the port with a metal plate. They figure that since EGR reduces the amount of air and fuel entering the engine, the EGR system costs them some performance. This is flawed reasoning.

Why an EGR delete doesn’t help increase performance

The entire reason for EGR is to reduce air/fuel volumes when the engine doesn’t need as much power. So the EGR valve is only open at low speeds when performance isn’t even an issue. As you put the pedal to the metal to get more power, the EGR closes, shutting off exhaust gas flow, so deleting the EGR offers NO benefit whatsoever—it’s closed when you’re asking for power. How does deleting it add any power if it’s closed to begin with? It doesn’t. Deleting the EGR valve is stupid and illegal. It’s considered tampering with the emissions system and deleting it adds to pollution.

Deleting an EGR valve can cause engine damage

Remember that the main purpose of the EGR is to reduce combustion temperatures in order to reduce NOx formation. An EGR system reduces combustion temperatures by around 300°F. If you delete the EGR valve, you actually increase combustion temperatures at idle and low power periods. Increasing combustion temperatures can cause premature exhaust valve and seat wear.

Worse yet, you can cause engine knock due (detonation)to the higher combustion temperatures.

Finally, in diesel applications in late-model vehicles, the EGR is responsible for diverting EGR flow to the diesel particulate filter first. If you delete the EGR valve,  you remove the diversion and actually introduce more soot into the combustion chamber, thereby increasing sludge formation.

There is NO advantage to an EGR delete. You don’t get more power and you create more pollution.

EGR trouble codes

How an EGR valve fails

EGR valves operate in a high-heat hostile environment. Exhaust gas contains soot and unburned fuel. Over time the valve pintle and seat can accumulate carbon buildup that prevents the EGR from fully closing. The carbon buildup can also cause pintle binding, preventing full or partial opening/closing.

Carbon buildup can also occur in the exhaust manifold and intake manifold passages, reducing EGR flow.

When passages clog or the valve can’t fully open or close, the expected exhaust flow doesn’t match the commanded exhaust flow. When that happens, the PCM sets a trouble code.

Signs of EGR valve failure

Check engine light— When passages clog or the valve can’t fully open or close, the expected exhaust flow doesn’t match the commanded exhaust flow. When that happens, the PCM sets a trouble code

Engine performance issues: if the EGR valve sticks open, the exhaust flow will dilute the air/fuel mixture to the point where it affects engine performance. So you can experience reduced power, poor acceleration, and rough idle. It may also produce turbo boost pressure leaks, causing the turbo to work harder.

Increased NOx emissions — A stuck shut EGR will cause you to fail an emission test due to higher than allowed production of NOx.

Engine knock— the higher temperatures and NOx may also result in increased detonation or knock, heard as knocking noises in the engine.

Common EGR fault codes

On late model EGR valves the following fault codes are common:

P0400: EGR flow malfunction. When the PCM commands EGR, it expects to see the results in engine RPM and O2 sensor readings. If the results don’t match expectations, the PCM sets a P0400 trouble code.

P0401: EGR insufficient flow detected—This might be caused by carbon buildup in the exhaust passages or a buildup in the EGR valve.
P0402: EGR excessive flow detected— This is most often caused by a partially or fully stuck open EGR valve.
P0403: EGR circuit malfunction—In an electronically controlled EGR valve, this can indicate a short to ground, open, or excessive coil resistance.
P0404: EGR circuit range/performance—In an electronically controlled EGR valve, this can indicate a short to ground, open, or excessive coil resistance.

Sensor range codes refer to the sensors used to measure how far the pintle has moved. A sensor range code indicates a problem between the commanded movement versus actual movement.
P0405: EGR sensor A circuit low—
P0406: EGR sensor A circuit high
P0407: EGR sensor B circuit low
P0408: EGR sensor B circuit high
P1403: EGR solenoid low
P1404: EGR system – closed valve pintle error
P1405: EGR solenoid high
P1406: EGR system pintle position error

©, 2021 Rick Muscoplat