The Exhaust Gas Recirculating (EGR) system was introduced to the 300tdi engine in around 1995 as an emissions control measure. The purpose of the system is to introduce small quantities of exhaust gas into the intake air to reduce its’ temperature  and thereby promote greater combustion. This, in turn, is designed to reduce the amount of nitrous oxide (Nox), a particularly nasty by-product of diesel combustion, in the exhaust gases.

The system comprises a valve attached to the exhaust manifold that controls the flow of gases through a small link tube to the intake air pipework between the intercooler and the inlet manifold. The valve has an electrical connection to a micro switch assembly mounted on the fuel injection pump and a vacuum connection to a small manifold located on the inner wing in front of the air filter box. The operation of the valve is determined by the throttle position such that the valve is closed at tick over and at full load, but open at mid-range throttle positions.

In practice, it’s been found that the main function of this system is to merely coat the inside of the latter part of the intake air pipework and the inlet manifold with oily crud, which does little for performance and economy. It’s therefore become quite common to blank off this system where it attaches to the intake air pipework and it’s even possible to buy specially shaped little plates to do it with.

Whilst I was cleaning my original intercooler some time ago, I made and fitted my own little plate, but when I had an uprated intercooler along with silicon hoses fitted by Allisport I asked them to remove the complete system. First to go was the valve itself, and a neat plate was fitted to the hole in the exhaust manifold, sealed with exhaust paste. The link tube to the inlet pipework was removed, still attached to the inlet pipe itself, which was in turn replaced by a new silicon hose.

The thin pipe was disconnected from the vacuum manifold and the resultant hole plugged with a short length of rubber pipe with a bolt in the end. The micro switch assembly was unbolted from the fuel injection pump and unplugged from the wiring loom. The loom itself between the EGR valve and the injection pump was merely coiled up out of the way as it disappears into a much larger engine bay loom at each end and would be difficult to separate.

I’d had the EGR valve blanked off for quite some time before it was removed completely and I must say that I noticed little, if any, difference in performance. It was always satisfying to know that the exhaust crud wasn’t being fed back into the engine though, and having the complete system removed does tidy up the engine bay.

As an aside, the vehicle passed several MoT emissions tests with this system blocked off without any problems.