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45bhp CDI EGR Clean

Mod Description
Diesels are dirty engines, they are noisy but they are efficient. However, if they can't breathe then you aren't getting the best from the engine.
Mod Details
PremiumYes Difficulty Mod ID905 Creditevilution For451 Fortwo Link Copy to Clipboard

What Is An EGR?

It stands for exhaust gas recirculator. It’s a very simple system that routes some of the hot exhaust gasses back into the engine to further reduce emissions. When Nitrogen and Oxygen burn at high temperatures inside an engine, they create a a gas called NOx. This is a generic name for Nitrogen Oxide (NO) and Nitrogen Dioxide (NO2). NOx is a pollutant that causes smog and acid rain.

The NOx gas is not flammable so pumping some back into the engine replaces some of the normal air, this reduces combustion (at some loss of efficiency and power) which reduces combustion temperatures. This in turn creates less NOx in the first place.


Making the combustion less efficient creates a lot of unburnt fuel which increases the particulates emissions. It is these particulates that have forced manufacturers to create DPF (diesel particulate filters). These catch the particulates but these filters clog up over time and need heating up to burn off the particulates. The DPF is heated up by running the engine hotter which in turn creates more NOx. It’s a vicious circle but it’s just the car manufacturers cheating the systems to get the emissions down so they cost less to tax. Luckily the 45bhp CDI doesn’t have a DPF.

Exhaust Gas Is Dirty

Indeed, it’s mainly full of unburnt carbon which you will know as soot. When you add soot filled gas into a pipe that has burnt oil vapour in it as well (from the crank case breather pipe) you get an absolute mess. It sticks to the inside of the pipework and quickly reduces the amount of air getting into the engine.

How Bad Can It Possibily Get?

Below is the EGR mixing body from my 45bhp CDI. This was only 40,000 miles old and you can see that more than half of the airway has been blocked by a baked on mixture of soot and burnt oil.

It really needs cleaning out. Oh, 1 big tip. Wear gloves!

Removing The EGR Mixer Body

Open the engine bay to reveal the thing that’s going to make you filthy.


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