[Rincewind]

The whole EGR debate continues to rumble on.

I for one find it increasinly frustrating that there are so many people out there determined to by-pass them or turn them off etc when manufacturers spend so much time and effort getting them into vehicles to help reduce emissions with minimal impact on engine performance and so on.

I've just done some test work out in Italy on some diesel engines for emissions and fuel economy and also engine power and the results that I had with a "by-passed" EGR valve or failed unit as is would be viewed are amazing.

With the EGR valve working as it should the results were as follows:

CO - 0.306 g/km 41.3% of the limit for Type approval for this vehicle.
NOx - 0.323 g/km 82.8% of the limit for Type approval for this vehicle.
HC + NOx - 0.356 g/km 77.4% of the limit for Type approval for this vehicle.
PM - 0.026 g/km 52% of the limit for Type approval for this vehicle (particulate matter).

Then for OBD purposes, we have to fail the system or by-pass it to see if the system falls within the OBD limit requirements in this instance, it's fully open like a by-pass system would be.

The results are as follows (OBD limits are different, but look at what the TA limit comparison is) :

CO - 0.210 g/km 31.2% of limit. So far so good.
NOx - 1.783 g/km 457.2% of the limit - so massively over the limit!!!
HC + NOx - 1.859 g/km 404.1% of the limit - massively over the limit again
PM - 0.161 - 268% of the limit.

So as you can see, on a normal drive cycle for emissions testing the results go through the roof and are almost like running a vehicle from god knows how many years ago. Not to mention that the drivablility of the vehicle falls through the floor to begin with until the ECU "smooths" things out and then over a few cycles, the MIL will come on to show that there is a problem in the engine which is then stored in the memory until taken out and should you get pulled for a road side emissions check (which is starting to happen again very soon) they will be able to access your ECU and find out how far you've driven with a defecive EGR valve or other.

Fuel consumption also suffers on Phase 1 of the test by up to 1 litre in the urban cycle.

Keeping it clean is always a good thing as it improved efficiency, but bypassing it is a real no no in my books. MOT emissions sniffs are just that, sniffs and if you were to put your car through a proper emissions test like the one's I have to witness for type approval, your car would fail the emissions test. for either Euro III which all of our cars are type approved to and they wouldn't even get close for Euro IV.

Yes, they are predominantly there for emissions, but given the lengths manufacturers go to fit them into the engines and callibrate them etc with minimal impact on performance costs thousands and many months of development so I hope you can begin to understand why I and my fellow engineers who deal with engine development get totally hacked off when people start by-passing them all for the sake of a few BHP which you're never really going to notice.

Sorry, my 2p's worth but from where I sit, they're there for a very important reason. I hope you understand my frustration.

Nic