EGR Valve function

Can anyone please explain to me the functioning of the EGR valve - I know it recirculates some of the exhaust gases back into the combustion chamber, but how does that reduce the combustion temperature (I believe that's what it does, so that the NOx emmissions are lower).

If one has to disconnect the EGR valve, what precautions should one take?

thanks.

[Mike Richards]

The EGR is part of the emission control system. Would disconnecting it trip a CHECK ENGINE light and/or cause the vehicle to fail an emissions test?

[stevebfl]

EGR is used to introduce an inert gas to take up space so to speak. It quenches the flame and by doing so it can hold combustion temps to below the range where Nitrogen oxidizes.

So the inert gas would affect the performance of the car adversely, right (in terms of acceleration)? How about the fuel economy? What would happen if one disconnects it?

Thanks.

agupta: I have always believed - if the car was designed to use a part to run properly - don't redesign it - FIX THE PROBLEM. If the car runs better without the part - something is wrong - I firmly believe - two wrongs don't make a right. Just my opinion - Whether or not performance would be affected (Idon't know) - emissions will go higher.

[surfblau]

Along the lines of the original post, I was wondering what the potential risks are with disconnecting the EGR (on my 84 TD).

I believe that the vacuum unit that controls the EGR valve on my car has a leak, and am wondering if it is worth replacing, or just plugging the input vacuum lines. I will study the emmissions schematic more before doing so, but it looks like there is only one line to the EGR valve, and this proceedure would disable the EGR.

I have seen other posts that describe using a bb to plug that line, but I was still wondering if there are any risks.

thanks

[Jeff72_220d]

On a diesel car, particularly the older 1980s types:

The "bb fix" only works if the rest of the vacuum system does not have leaks. If you are in a state where you are not inspected, you can get away with disconnecting the entire egr system, including the two "white valves" that are a part of it. Simply disconnect the two vacuum hoses as close to the main vacuum line (the larger diameter one) as you can. Plug the two locations at the rubber connector. The car will probably run better.

On a gasoline car:

If you are in a state that inspects (such as California) the emission control system, you will get busted, unless you re-connect the egr before the inspection. On more modern cars, that use numerous sensors and have a computer controlled system, you will be better off repairing any leaks and/or egr parts to get the car to operate properly.

[mbdoc]

One of the reasons (many) not to disconnect EGR is the fact that engines ARE designed to run on this partially burnt fuel/air mixture. Disconnecting can cause engines to run HOTTER esp. on the DIESEL models!