Rick's Free Auto Repair Advice

EGR delete

EGR delete — good or bad for your engine?

An EGR delete doesn’t get you more power and can damage your engine. The people who recommend it don’t fully understand how an EGR system actually helps your engine run more efficiently. They misconstrue the benefits of air/fuel dilution. If you’re thinking about performing an EGR delete on your engine, read this first.

Why engines use an EGR valve

To improve MPG, most modern engines burn a leaner air/fuel mixture. The engineers use a variety of methods to ignite the lean mixture including better vaporization techniques and swirl chambers in the cylinder head. However, once a lean mixture finally ignites, it burns at higher temperatures than older richer burning engines. In fact, it’s not uncommon to see a lean-burn temperature in the 2,500°F range.

At that temperature inert gasses become reactive, creating oxides of Nitrogen (NOx), one of the main components of smog. It’s an eye and lung irritant.

Just as important, the extremely high combustion temperatures cause pre-ignition, where combustion begins before the spark plug fires. This results in multiple flame fronts colliding in the combustion chamber, causing knock.

To reduce NOx emissions and reduce the occurrence of pre-ignition/knock, engineers needed to reduce combustion temperatures while still maintaining a lean air/fuel mixture. EGR is one way to accomplish both goals.

EGR valves also cool the air/fuel mixture in diesel engines. Some diesel engines use an EGR gas cooler to remove heat from the incoming exhaust gas to further reduce combustion temperatures.


A lean burn engine improves MPG but results in higher combustion temperatures
Higher combustion temperatures create oxides of Nitrogen (NOx)
High combustion temperatures result in pre-ignition and knock.
To reduce NOx and meet emissions standards and to reduce pre-ignition, engineers had to either:

  1. Richen the mixture to reduce burn temperatures, or
  2. Reduce combustion temperatures by adding a non-combustible ballast gas; something that would take up space in the combustion chamber but not burn.

How an EGR valve works

Introducing a non combustible gas at idle or low RPMs dilutes the air/fuel mixture, which can cause the engine to idle roughly and stall. So the EGR valve is fully closed at startup. Once the engine warms up, the EGR valve opens at low speeds and partial throttle. By introducing exhaust ballast at low speeds, the EGR dilutes the air/fuel mixture which reduces the peak combustion temperature.

However, diluting the air/fuel mixture also reduces power. So you’re forced to push harder on the pedal to open the throttle wider. That adds more air while the fuel injection adds more fuel. Opening the throttle at low speeds, reduces pumping losses (the power lost when the piston has to suck against a closed throttle plate during the intake stroke). In other words, by adding exhaust ballast at low speeds and forcing the driver to open the throttle, the engine actually becomes MORE efficient.

At higher speeds, where more power is needed, the EGR valve remains closed, cutting off all ballast introduction and allowing for a full air/fuel mixture delivery.


  1. The EGR valve reduces combustion temperatures at low speeds, reducing NOx and pre-ignition/knock.
  2. The now-lower peak combustion temperatures prevent the reactive phase where NOx is normally formed, thus allowing the air/fuel mixture to release more energy.
  3. The loss of power due to EGR ballast forces the driver to open the throttle, which lowers pumping losses thus increasing engine efficiency.

What happens when you delete the EGR valve?

  1. You raise combustion temperatures to the 2,500°F range.
  2. The high combustion temperatures start the reactive phase which wastes some of the thermal energy of combustion as it creates NOx.
  3. You create NOx which pollutes the air and causes the vehicle to fail emissions testing.
  4. You trigger pre-ignition events which are seen by the engine’s knock sensor. In turn, the computer retards ignition timing, thus reducing engine power.
  5. The hotter combustion temperatures transfer more heat to the cylinder walls and valves, thus reducing the amount of energy available to produce mechanical work. The higher heat transfer to the cylinder walls and valves, erodes the exhaust valve faces and seats, causing misfires which can only be fixed by performing a valve job.
  6. Overall, deleting the EGR valve reduces engine life and provides little to no power boost since it’s only operational at idle and low throttle.

©, 2020 Rick Muscoplat


Posted on by Rick Muscoplat

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