what does the computer think with no egr?


Jul 4, 2004
Carmel, New York
im deleting my egr while my motor is apart. I had no worries until i read this off the new pro m site:

What other things will cause my car to go into limp-home mode, or cause the ECU to not read my MAF?

-A disconnected EGR sensor. It does not have to be a functioning EGR system, but the electronic portion of the EGR sensor needs to be connected to the vehicle wiring harness.

so when it throws the check engine light, what is ithe computer going to do?
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Some who have deleted the mechanical parts of the egr system and left the ecu alone have reported part throttle timing issues (detonation/ping), but others seem to be ok. It seems to be a 50% chance that things will be ok.
You are posting in the tuner forum so I guess you will be turning off the functionality of the egr with a tweecer or equivalent?
When removing the egr this is really the only way to do it right.

Here is an old thread that does a decent job of explaining what the egr is for and how it works.


In summary...
The EGR is an emissions device that reduces NOx by decreasing the combustion temps. Nitrogen Oxides are only formed when enough Oxygen and Nitrogen are present and combustion temps are very high. Small reductions in combustion temps can have large effects on NOx output. EGR reduces combustion temps by displacing Oxygen from the intake charge with an inert gas (Recirculated Exhaust). The decrease in Oxygen lowers the efficiency of the combustion process, and therefore the temperatures reached during combustion.
Due to the decrease in the efficiency of the combustion process, our computers will add spark advance when the EGR is functioning. The EGR will function at part throttle conditions only. The EGR is turned off at WOT, and therefore has no affect on WOT power. Since the efficiency of the combustion process is being decreased, less power is being created. This will cause the driver to open the throttle a little more, to maintain an appropriate level of power for the driving situation. An open throttle body is easier for the motor to breathe through - the pumping losses are lower.
Due to the fact that the spark can be advanced and that the throttle can be opened farther (reducing pumping losses), one can actually see a gain in fuel economy due to the use of EGR.
Summary- the EGR does not affect WOT power, and can improve part throttle fuel economy. Additionally, since the computer is adding spark advance when the EGR should be functioning, removing the EGR (and not telling the computer that the EGR is gone) can result in some very bad ping/detonation at part throttle.