Pollution pump

The pollution pump was an early automobile emissions-control device. It consisted of a small device that pumped exhaust from the engine back into the intake, thereby re-burning the mix and burning off some of the pollution. This was particularly effective during acceleration, when extra fuel/gas mixture, the charge, was pumped into the cylinder and wouldn't burn cleanly.

Pumping hot, dirty air into the cylinder has negative effects on the gas mileage, but the pump was a simple device that could be added to existing engines. It saw widespread use in the 1970s. Newer engines have turned almost entirely to fuel injection, which eliminates this problem entirely, and without a pollution pump, the relative gas mileage improves.