Exhaust Gas Recirculation Question!!

[Big Red]

Hey guys I think that this is going to be a really technical question. I just recently bought another Ex. except this is a '94 XLT. I bought it from a friend and I have been hearing this funny sound that sounds like plastic slipping gears. (I know your saying what the heck am I talking about but that was the best way to describe it) Later my dad listened to it and said it actually sounds like a blown gasket or a vacuum leak. Well after a little bit of inspection we found a hose that has a little valve coming out of it that has nothing connected to it. So I made a little plug and closed the hole up. That was all it took and the annoying sounds is completely gone. Now I read up about that house with the valve sticking out of it and found that the house is called a "Exhaust Gas Recirculation (EGR) valve to exhaust manifold tube". The big question remains what does that little valve do and is it important. If it is not that important I can just plug it permanently and I won't worry about the noise. But if it has a specific purpose then what does it connect to and how. I appreciate any help and if you have any questions I will check this regularly to answer them.

Thanks, Big Red

 

[dogfriend]

The Exhaust Gas Recirculation (EGR) system is designed to reintroduce exhaust gas into the combustion chambers, thereby lowering combustion temperatures and reducing the formation of Oxides of Nitrogen (NOx).

http://www1.autozone.com/servlet/Ui..._us/0900823d/80/0e/2f/4e/0900823d800e2f4e.jsp


So if you are missing a hose from the EGR, you either have an exhaust leak, a vacuum leak or both.

You should repair it rather than blocking it off because:

1. You will put out more NOx (smog).

2. Your engine is calibrated for EGR so without it the fuel mixture will not be correct because the PCM thinks that it is working.

 

[Big Red]

This is great but can you please explain a little more... I tried to figure out what part of that diagram pertains to me but it is not making any sense at all. I appreciate your input.

 

[bikeboarder]

the EGR sucks exhust in to the intake to reburn unburnt fuel. so it could be fine i don't have one at all and still pass emitions. it might run a little lean but IMO nothing to loose any sleep over.

 

[dogfriend]

If you follow the link above, there is a lot more information but I posted the diagram because it shows how the various parts work together.

The basic idea of the EGR system is that it recycles exhaust from the exhaust manifold and redirects it into the intake manifold where it gets sucked into the cylinders again. The reason to do this is to reduce the amount of a certain type of smog (NOx). The exhaust is only recycled under certain conditions (warm engine, light load) so that it doesn't hurt engine performance.

The PCM opens (and closes) the EGR valve by sending a signal to the EGR Vacuum Regulator (EVR) which then applies vacuum to the diaphragm in the EGR valve. The PCM reads a signal from the DFPE sensor to determine if the flow of exhaust is correct. The PCM uses this information plus other sensor information (coolent temp, engine load, etc.) to determine how much to open the EGR valve and when to open the EGR valve.

You can probably get away with blocking off the tube, but as I explained above, it would be better to fix it. Because the PCM is expecting to see some EGR flow, it will likely set a diagnostic code and it may cause the fuel mixture to be incorrect when the EGR valve should be open.

 

[mrboyle]

the EGR sucks exhust in to the intake to reburn unburnt fuel. so it could be fine i don't have one at all and still pass emitions. it might run a little lean but IMO nothing to loose any sleep over.

The reason your X passes emissions w/o an EGR valve is because it was not equipped with one from the factory and there by is not required to have one.

 

[shamaal]

Mr. Boyle is, of course, correct. The 91's did not have an EGR valve. I have enclosed a diagram of the vacuum system. Not shown on the diagram is a check valve for the environmental controls. That's the thing in the center of the 'T' formed by the vacuum hoses in the second diagram. If you have a picture of your valve that will help tremendously.