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are there any benefits from disconnecting the egr valve & will it do any harm to the engine hdi 90
also i know its illegal but does fitting a de-cat pipe give any extra power.

thanks alan

welly mentioned something about disconnecting egr valve
be interesting to see if anyone has any thoughts on this ...

You can blank off the egr valve and stick a bung in the vacuum pipe.

As for the decat I'm not sure its worth the bother, lot of hassle taking it out/putting it back for the mot for a possible couple of bhp. For more power your best off going for a remap, these guys seem to do the business. Will be getting mine done by them next month. There are a number of members on here now who have used them.

Fog

so what exactly does blanking the egr off do foggy

Not sure really, as far as I understand it all the EGR does is redirect the exhaust gases back into the inlet to be reburnt, theoretically improving emissions. In practice it gets very sooted up and gets a bit stuck.

I managed to get a brand new genuine one for mine last year off eBay for the princely some of £12, they're ALOT more than that from a dealer.

Fog

and wtf IS an egr valve anyway?

Exhaust Gas Recirculation valve.

Fog

What is the point of it? Surely it'd be easier, cleaner and less damaging to just use fresh air?

alan forbes wrote:are there any benefits from disconnecting the egr valve & will it do any harm to the engine hdi 90
also i know its illegal but does fitting a de-cat pipe give any extra power.

thanks alan

decat is not illegal on a diesel, well worth it as you will get much less turbo lag, and slightly more boost higher up the revs, though the later is useless on a HDi 90 as boost is mapped not measured

mjb wrote:What is the point of it? Surely it'd be easier, cleaner and less damaging to just use fresh air?

it lowers the combustion temperature, not quite sure why but it does, and thus less oxides of nitrogen are emitted (NOx) as less fuel is needed to be burned

Well chaps,

Exhaust gas recirculation (EGR) systems were introduced in the early '70s to reduce an exhaust emission that was not being cleaned by the other smog controls. Oxides of nitrogen (NOx) are formed when temperatures in the combustion chamber get too hot. At 2500 degrees Fahrenheit or hotter, the nitrogen and oxygen in the combustion chamber can chemically combine to form nitrous oxides, which, when combined with hydrocarbons (HCs) and the presence of sunlight, produces an ugly haze in our skies known commonly as smog.

How EGR systems work:

The EGR valve recirculates exhaust into the intake stream. Exhaust gases have already combusted, so they do not burn again when they are recirculated. These gases displace some of the normal intake charge. This chemically slows and cools the combustion process by several hundred degrees, thus reducing NOx formation.

I wrote that all by myself, yes I did

I thank yaw.

wow that was shockingly informative! thanks welton

mjb wrote:wow that was shockingly informative! thanks welton

You mean 'shocking for me to come up with that' don't you, I do have some useful intelligence, somewhere.

If you think about the way an EGR works then you would naturally assume your car should run faster without it (given that the oxygen content of the cylinders will be higher). It is not a widely recognised 'tuning mod' to remove your EGR though - otherwise we'd all be doing it

removing the egr was a common mod on the mondeo TD's but not done on the pugs much.

posted a newbie qu about this too.
The advantages of doing it seem to be where the design of the valve cut off lots of airflow from the intercooler into the inlet manifold. Rover/BMW 2.0d ones are very restrictive and the result feels like the change from a 2l to a 3l Diesel! Smoother and easier revving.
The disadvantage seems to be that the engine will run hotter as there is no "inert charge of air" entering in the exhaust gas into the combustion chamber, but Roverron seemed to think that as the EGR is disabled on full throttle, it doesnt really make a great deal of difference. But, if there is more combustion, more power should result, but also more fuel used. So mpg gains may be marginal or actually worse, I'd say from my experience. In MGR circles, an EGR bypass casting is selling well for about £45, by a chap who also does exhaust systems.