E30 Zone

My previous daily was a astra 1.7 dti and one of the first mods I did was to fit a blanking plate for the egr as they are known to go faulty read lots about the benefits at that time such as better pick up and improved mpg, from experience can't comment on mpg improving but pick up was much better as the car felt it had much more bottom end torque. I've now bought myself a corolla d4d and was going to do the same thing as I do mostly local trips and this would prob clog the valve up sooner so I did a bit more reading on if its a good idea and there's mixed opinions on the topic. My understanding of the egr valve is that it reduces combustion temp as a higher combustion temperature generates more nox which can be dangerous for the engine. Some people argue that the valve is designed to be there and blanking it will cause higher combustion temperature and nox which can cause a head gasket to blow but then others argue that the egr only works at low rpm so on motorway speeds the valve is not operating meaning that the combustion temps and nox would be same as the valve being blanked so the engine must be able to handle it, can anyone explain theoreticly how it could improve mpg as I find that hard to believe.

On a Diesel, the EGR only tends to work at cruise, so 50mph on an A road or 70mph on the motorway.

Because manufacturers have to reduce CO and HC particles, they run the engines leaner. However, oxygen burns hotter than petrol, so you get NOx formation, which you quite rightly said forms at higher combustion temperatures.

So the solution is to run a large amount of EGR. Not only does this get rid of more unburnt HC's but also helps lower the combustion temperature. The downside is it absolutely gacks everything up inside the intake system.

With regards to power, exhaust gas that should be spooling your turbo is going back into the engine, you get less oxygen into the cylinder.

I would highly doubt blanking the EGR valve is going to blow a head gasket, but I'm willing to be proved wrong.

As to MPG, what you probably notice more is an increase in useable power. This means you don't have to press the accelerator as much and use so much fuel.

I did this as a mod to my TDCi mondeo

Didnt notice any increase in power or MPG but after the hideous jobs of cleaning out the EGR and manifold which took 4 cans of carb cleaner I really didnt want to do it again.

Certainly didnt notice any adverse effects - the only thing to bear in mind is that on some cars the EGR has an electrical sensor on it and if you blank it off it will put the engine management light on. Mechanical EGR's can usually be blanked off with no ill effects as far as I know.