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Most people don't understand what the EGR system does on any car so don't feel bad.
Unburnt fuel in the exhaust is taken care of in the catalytic convertors.
Nik is right, the purpose of the EGR is to reduce NOx.
The exhaust gas acts as an inert gas (only about 2% oxygen vs. ~16% pre-combustion), this allows higher compression ratios yet with lower oxygen the flame propagation is slower and combustion temperature is lower. So lower combustion temp = lower NOx and less prone to spark knock.
Most cars with defective EGR systems will experience either spark knock (detonation) or lower mpg &/or performance as the knock sensor(s) will retard timing to avoid engine damage from the knock.
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ASE Certified Master Automotive Technician w/L1.
ASE Certified Master Medium/Heavy Truck Technician.
Certified EVT (Emergency Vehicle Technician)
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