EGR - Exhaust Gases Recircluator - so what does it do besides recirculate the gases - mainly what the one guy explained, So why did they put it on there, partly to reduce smog polution, But it's main reason was to stop spark knocking. Yes, a Diesel will spark knock just like a gas engine will! Partly due to low cetane or low octance for gas car.

When all of this polution stuff came about, spark knocking was a real problem and so to try and stop this from happening, they came up with the bright idea to recirculate the exhaust gases in hopes of stopping that horrible sound. Try to reburn the excess gas. For the most part, it did work.

But it only worked part of the time and on only some cars and pickups. So early on, people found that the valve was also Clogging things up! Like the intake getting clogged (yes a gas engine will get terribly clogged). I had to change an intake manifold once to get a clean open intake! So they found they could block it off and the car ran fine without it. You can disable it. It you car spark knocks, just use premuim diesel.