What does an EGR valve do?
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5.0 and 5.7 Discussion, What does an EGR valve do? in Cadillac Engine Technical Discussion; Okay. I have a '95 Fleetwood Brougham and if I hit the gas VERY lightly, like going in reverse or ...
  1. #1
    Lord Cadillac is offline Cadillac Maniac
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    What does an EGR valve do?

    Okay. I have a '95 Fleetwood Brougham and if I hit the gas VERY lightly, like going in reverse or very slowly in drive - it feels like I've got a miss. Someone mentioned to me that the EGR valve may need replacing.. So what does it do?
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    elwesso's Avatar
    elwesso is offline Cadillac Owners Master
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    Re: What does an EGR valve do?

    EGR stands for Exhaust Gas Recirculation.......

    What it does is it "cools" the combustion temp by letting burnt, and therefore inert gas enter the combustion chamber......

    The valve is the apparatus that controls how much exhaust gas goes into the intake collector........

    Usually what happens to cause EGR failure is either clogging of the EGR passages, or the EGR valve sticking, either in a partially open, fully open, or closed position........

    I dont know if the EGR design is the same as on the Q, but you can test its operation by pushing up on the valve at idle, and if the speed decreases then its working.......

    If I recall correctly from previous posts, the EGR is constantly working, whereas on my car it ONLY comes on at cruising speeds.......

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    Re: What does an EGR valve do?

    Damn Wes, you were doing great 'til the last sentence. I know of no engine that applies EGR "constantly".
    Wes is correct right up until the last sentence Sal. By "diluting" the intake charge it stops detonation and cuts emissions among other things.

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    Lord Cadillac is offline Cadillac Maniac
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    Re: What does an EGR valve do?

    Wes is good - isn't he? So how much does it cost to replace one of these things? Can I do it myself?

    Thanks guys!

    Quote Originally Posted by Katshot
    Damn Wes, you were doing great 'til the last sentence. I know of no engine that applies EGR "constantly".
    Wes is correct right up until the last sentence Sal. By "diluting" the intake charge it stops detonation and cuts emissions among other things.
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    Re: What does an EGR valve do?

    On my car, the EGR valve is really easy to fix...... Just two bolts holding it to the plenum and one nut attaching it to the EGR tube...... Valve is something like 50, and maybe 20mins to replace...... If you can turn a wrench, you can do it........

    Id inspect EGR clogging and valve operation before I jumped the gun and replaced it......

    On my car, most EGR clogging occurs on the valve itself, on the intake colletor side....... The actual tube doesnt really get clogged........

    Kevin, can you test the EGR valve the same way as on mine........

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    A simple test of the EGR can be done with the car OFF by removing the vacuum line, pressing the diaphram in, then blocking the inlet with your finger and releasing the diaphram. It should stay in until you remove your finger.

    Remember though, your EGR valve is constantly being tested by the computer in your car. If it ever fails this test, you will see the check engine light and a code 32 will be reported on the OBD screen. (OBD1)

    The EGR test occurs while you are driving and these conditions exist:
    1. Vehicle speed is between 16-32 mph
    2. Vehicle is coasting
    3. Throttle angle is at 0%
    4. Transmission is in 3rd or 4th gear
    5. Manifold pressure is within certain range for barometric pressure (email me if you MUST have these values )
    6. No change in AC status
    7. No DTC 21,22,24,33,34 exist
    8. All above conditions continue for 2.5 seconds
    When this happens the computer signals the EGR valve "ON". If there is not a minimum 1.3kPa change in manifold pressure within 1.5 seconds of this signal, the test fails and you will get the check engine light.

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    p8ntman442 is offline Cadillac Owners Member
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    Re: What does an EGR valve do?

    I have found many times that when the egr code is set, that in fact the valve does no need to be replaced, but rather removed and cleaned. there is a lot of carbon build up on the needle of the valve and sometimes it will stick open or closed because the carbon having a greater hold on the needle than the pressure exerted on the top of the needle from the diaphram. I would suggest taking the egr valve off and spraying it down with a good amout of carb cleaner and working the needle back and forth several times, once it is nice and clean perform a vaccume test on it by either a vacume pump or the above test witht he finger over the hole. If it holds vaccume reinstall it and disconnect your battery for 30 seconds and then reconnect it, take it for a drive and see if it fixes the problem. If this fails, then go and purchase a new valve, I would suggest a dealer part, because aftermarket egr valves are garbage and will go bad in much less time than a gm one. I have attached a picture of a generic egr valve just so you can easily identify it on your intake.
    Attached Images

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    Re: What does an EGR valve do?

    The EGR system depends on not only the VALVE but the exhaust gas PASSAGES. Even if the valve functions properly, the "system" may not work if the passages are clogged with carbon. This is a VERY common issue on MANY cars. In this case, you may need to clear the passages before the problem can be fixed.
    Also one side note: Even though the EGR valve on the Fleetwood is an old style vacuum operated type, many newer EGR valves are "digital" and are operated via an electrical solenoid. These obviously CANNOT be diagnosed in the manor described above, and are easily identified by their wiring connection instead of a vacuum line connection. Also, EGR valve replacement can be a tricky issue on many vehicles due to the fact that there are several different types of vacuum-operated valves, and they all look alike. So I would agree that the safest path is to use the FACTORY replacement part.
    BTW, there is also a possibility that EGR operation can be inhibited by the installation of aftermarket exhaust systems since they change the amount of system back-pressure.

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    southflorida954 is offline Cadillac Owners Member
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    Re: What does an EGR valve do?

    What I was taught(in my own words):
    When the combustion temperature gets high enough(to high?), nitric-oxides are produced. They cannot be "baked" in the cat, and there isn't any another way to deal with these gases. The EGR system prevents these emissions from being created. The EGR system dumps exhaust gas into the combustion chamber(through the manifold or plenum), and sort of "dumbs down" the fuel mixture, preventing the combust. temp. from reaching a point where it produces nitric-oxides.

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    Re: What does an EGR valve do?

    On my LT1 EGR comes in between 900 and 2400 rpm, and only between certain vacuum conditions. And a lot of timing when EGR is active.

    The Corvette is less, like 1200-2100 rpm, and extra timing at times EGR is working. But not as much as the B/D car timing advances

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    kildysartkid is offline Cadillac Owners Member
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    Re: What does an EGR valve do?

    From Wikipedia
    EGR testing

    With OBD II standards, vehicle manufacturers were required to test the EGR valve for functionality during driving. Some manufacturers use the MAP sensor to accomplish this. In these vehicles, they have a MAF sensor for their primary load sensor. The MAP sensor is then used for rationality checks and to test the EGR valve. The way they do this is during a deceleration of the vehicle when there is low absolute pressure in the intake manifold (i.e., a high vacuum present in the intake manifold relative to the outside air). During this low absolute pressure (i.e., high vacuum) the PCM will open the EGR valve and then monitor the MAP sensor's values. If the EGR is functioning properly, the manifold absolute pressure will increase as exhaust gases enter.

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    Re: What does an EGR valve do?

    Attack of the zombie thread!

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