Read the advice on this site to disable EGR valve _ Exhaust Gas Recirculating Valves
What are they? What do they do? How do they fail??
EGR Valves have been around for a long time. Way back in 1972 GM used them in an attempt to reduce emissions of oxides of nitrogen (NOx) which were a major cause of air pollution, mainly photochemical smog, that kind of smog which is formed when strong sunlight shines down on the exhaust gasses we puke out of our tailpipes by the billions of cubic feet a day.
A short chemistry lesson is in order here. It was discovered way back when, that high combustion chamber peak temperatures (the really short duration high temperatures near the end of the combustion process) caused oxygen and nitrogen to combine chemically and form these oxides of nitrogen mentioned above. Most of the anti-pollution devices of the day did a pretty good job of reducing the other bad by-products of combustion, namely excessive hydrocarbons and carbon monoxide, however they tended to induce the formation of oxides of nitrogen. Something had to be done else we would all die of smog diseases.
The automotive engineers figured that they needed to do something to lower the peak combustion temperatures which only occurred under certain high load driving conditions. They figured they could do so at the expense of power and fuel economy but what the heck, ya can't have everything! If they could only add something to the combustion chamber that would act like sort of a fire extinguisher to cool the combustion temperatures that would do it.
So they invented a way to allow some very inert gas to get back into the combustion chamber only when needed. They needed a source of this gas - it wasn't air, cuz that contains oxygen and nitrogen which caused the problem in the first place. So they chose carbon dioxide. Where to get a supply of carbon dioxide . . . ??? Hmmmm, how about the exhaust system? That is mainly carbon dioxide and water (plus a zillion other noxious chemicals) Suppose we allow some of the exhaust gas to get back into the intake manifold under strict control and only when we need it? That would cool the combustion chamber and prevent the formation of the NoX. Maybe we should call it recirculated exhaust gas (REG??). But a guy named Reginald voted no cuz he didn't want his name associated with a car part, so they called it exhaust gas recirculation (EGR) since there was nobody around with that name.
Now we understand why it is there. And we understand what it does. So perhaps we should all keep em working.
- (#8292) Brian, 2 Feb 04 18:16
Umm, sorry to say it, but your info is for petrol engines, not diesels.
And it's only operational at LOW loads, to reduce the oxides of N.
The downside is, as you increase the amount of EGR, you will:-
a. increase hydrocarbon emissions
b. increase CO emissions
c. increase fuel consumption
d. increase soot production.
For the owner/ driver, c and d. are major issues. C for the obvious reason, d. because that soot comes back into the engine via the EGR, and the particles will stick to the walls of the intake tract courtesy of the oil film formed by the CCV system, resulting in a blocked manifold, increasing emissions and fuel consumption.
All the above data courtesy of Robert Bosch's diesel technology documentation. You may be interested to know that manifold blockage is a well known problem for VW TDIs.
- (#8292) david miller, 3 Feb 04 13:29
I've thought a lot about the EGR. Once I understood what it's doing, as above and in other discussions in the archives, I left well alone partly trusting Toyota's design and saying, "if it isn't broken don't fix it" - and partly following Brian's sentiment that we all have a duty to consider how much we pollute the place.
Then one day I though I'd experiment. I don't know about fuel consumption but it certainly made a noticeable improvement to pulling away from stationary. So I left it disabled.
So where does this leave us on general pollution? I'd've thought disabling the EGR (which only operates under low load conditions) is only a minor issue compared to running a relatively fuel-thirsty vehicle, or even any vehicle, at all.
But does it not help the pollution problem if we, who are able, continue to run old vehicles - up to a point?
Merely manufacturing any vehicle contributes to pollution, so make them last, and I'm working on the theory that a little bit of extra NOX is negligible compared to the consequences of burning 10 litres for every 100km I choose to travel, and nothing compared to the indirect pollution of making me a new car un-necessarily. Am I wrong?
- (#8292) Dave (Sussex), 5 Feb 04 06:58