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demystifying the EGR valve

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by **DONOTDELETE**, Sep 24, 2001.

    on my last motor, i just blocked it off, passing it off as a useless emissions device. have i overlooked something? is there a good side to this device? somebody wanna go into detail as to how and why it works?

    greg
     
  1. Burbinator

    Burbinator 1/2 ton status

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    Seeing how I have recently been schooled on how the EGR and emissions control devices work, I'll try to explain what I know. The function of the EGR (exhaust gas recirculation) is to redirect a portion of the exhaust gases back into the intake stream to both dilute the mixture and to cool down the intake charge to promote a more complete burn and to prevent the formation of nitrogen oxide (NOx). The valve is closed at idle (engine would run badly if exhaust gases were introduced at idle) and opens proportionately in relation to the amount of vacuum it receives. I know that it was improperly connected on my truck, which was a major contributor to it failing emissions. I would say that with tolerances going down for tested pollutants every year, the carbureted motor will eventually be "forced out" of the game for daily drivers due to their inability to precisely meter fuel (compared to injectors). Until that point, a vehicle that must conform to emissions standards is well advised to have it installed and operational. I'm debating on a TBI setup before next years emissions test, but the EGR will still be intact either way. Hope that helps!

    - Alan

    '82 K10 Suburban Silverado (AKA U.S.S. Nimitz)

    Terrorists are good for one thing...FERTILIZER

    GOD BLESS AMERICA!
     
  2. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: GIVE THAT MAN A TROPHY!

    YES!!!!!! SOMEBODY GETS IT!!!!!!
    The end result of all your mumbo jumbo has a little more to it. When we lost lead fuel we lost some lubrication and we also lost a way to control some detonation/ flash rate. On a engine that was designed to run a EGR (Even on a engine that was designed to run leaded and didn't have a EGR) if you block it off it's more inclined to Detonation on unleaded fuel. The EGR (and the lead) will reduce this because it slows some of the explosion, or I should say it raises the flash point making sure that ignigtion is more predicatable, making it a more controled burn. Without the exhaust gas present it will burn to quickly and unevenly or spontaniously without ignition spark. It is a little more sensitive to hot spot ignition from say carbon build up. It effectivly raises the flash point like the lead did and higher octane does. The end result when it's blocked (or on engines that were designed for leaded fuel) is ping/detonation under load. On a Lead engine the cure is running it rich (or retarding the heck out of the timming causing the same effect by lowering combustion chamber temps) unfortunatly that is at the cost of higher emmisions and lower economy.
    On a FI engine equipped with a knock sensor you will loose power by blocking the EGR because the Knock sensor will pick up the ping/detonation back off the timming. This can confuse the computer because the O2 Sensor will not see the mixture being off with detonation but once the timming gets backed off it will see a change. It may respond by backing off the fuel to try to get the temp up. Remember a O2 sensor reads Exhaust temp. Hot = Lean, cold= rich. In this instance since the timming was retarted it would be under less compression when ignigtion occured so it would be a colder exhaust dump. The ECU will back off the mix to try to get more heat and guess what this does? It gets it into more of a detonation problem and more power loss.
    Sound like your going to school to be a mechanic. Remember a engine is just a series of events. Whne you diagonosing a failure you need to take your end result and work backwards to the cause. Once you understand exactly how the engine works it's simple to back track to a failure.

    I don't need no damn shop manual, I got a pornographic memory.
    <a target="_blank" href=http://communities.msn.com/OffroadK5s>communities.msn.com/OffroadK5s</a>
    75 Jimmy, Dollar
    Grim-Reaper
     
  3. Burt4x4

    Burt4x4 3/4 ton status

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    Re: GIVE THAT MAN A TROPHY!

    OOouuuu AAhhhhhhh the Grim-Reaper has spoken!! All rise!! Ok now you may be seated, class has begun!
    hewheeehe Sweet brain dump Grim!!

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
    <a target="_blank" href=http://www.geocities.com/baja/5099>www.geocities.com/baja/5099</a>
     
  4. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    What does that mean for after amrket intakes that do not have provisioning for an EGR valve? Is my engine going to be giving me problems related to your explanation down the road since I have no EGR?

    I have a 454 with a 750cfm Holley (yuck!) and a Edelbrock Air-Gap intake. What should I do?

    <font color=red>Just give me a tank, and point me in the right direction!</font color=red>
    <font color=blue>DONT MESS WITH AMERICA!</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Re: GIVE THAT MAN A TROPHY!

    Pretty good explanation until ya got to this part: <blockquote><font class="small">In reply to:</font><hr>

    Remember a O2 sensor reads Exhaust temp. Hot = Lean, cold= rich. In this instance since the timming was retarted it would be under less compression when ignigtion occured so it would be a colder exhaust dump.

    <hr></blockquote>
    An O2 sensor is actually an oxygen powered battery. The output voltage varies in direct proportion to the amount of oxygen in the exhaust stream. The chemical process for an O2 sensor to work requires that the sensor itself be at least 600 degrees F. Below that temp, the sensor is producing no voltage and the engine control computer switches to "open loop" mode, meaning that there is no feedback from the O2 sensor, so the computer calculates a "best guess" as to how much fuel to provide, based on data it has stored in memory.

    Some O2 sensors include a 12 volt heater to keep the sensor hot all the time. You'll see these referred to as 3-wire or 4-wire sensors. Our trucks have a single wire sensor that uses the exhaust system as ground and relies on exhaust heat to warm up the sensor element. According to the GM service manuals, it's possible for our engines to switch into open loop mode during long periods of idling since there isn't enough heat being produced to keep the O2 sensor up to temp. This is even more likely with headers, since they don't have the thermal mass to hold the heat in.

    If you want lots more details, check out this explanation at the the Bosch website:
    <a target="_blank" href=http://www.volksparts.com/o2sensors.htm>http://www.volksparts.com/o2sensors.htm</a>

    <font color=black>HarryH3 - '75 K5</font color=black>
    <a target="_blank" href=http://www.angelfire.com/super/ThunderTruck>www.angelfire.com/super/ThunderTruck</a>
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  6. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: GIVE THAT MAN A TROPHY!

    It means NOT LEGAL FOR STREET USE (Read the disclaimer that comes with it). Off road use only if it's on a car that came with a EGR is what it means. It also means run it rich and smelly and put 93octane in it. That should be no problem to run rich with that holly.
    You can run the thing if you don't have emmisions checks where you are but like I said you going to need to run rich and probably recurve your advance and might need to run a lead substitute or a octane boost if the 93 doesn't take care of the ping. Where you get into real trouble is if youwere trying to run that with a factory FI. With a Carb it will be ok because it's not going to fight running rich. Without the gas additives depending on your compression ratio you might have to back down a couple degrees of timming. May need to run a hotter plug also.
    My stock 75 that came with no EGR and was still designed to run lead fuel I have fought all sorts of ping issues. Most of them I cured with cleaning the distributor up and getting some cool air to the intake by installing a later model snorkle set up. I was just about to the point of putting on a EGR intake I have and running a newer emmission carb. Finnaly found the right ballance to get it to run on 89 octane. It will not run on 87 it wan't 93 but at 10mpg you can forget that. On the Lady's 79 with a properly working EGR it will not run right on 87 either. But that is a fresh Crate and I do have a couple degrees of extra advance in it. It passes emmision fine ifact really good on the lower end of the limits.
    What did you do with the FI that came on your truck? is it for sale?

    I don't need no damn shop manual, I got a pornographic memory.
    <a target="_blank" href=http://communities.msn.com/OffroadK5s>communities.msn.com/OffroadK5s</a>
    75 Jimmy, Dollar
    Grim-Reaper
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: GIVE THAT MAN A TROPHY!

    Good information and you did get me on the operation of the O2 sensor. I'll give you that and I will file that information in my noggin for the future.
    I always associate it to the amount of heat present. In a simple form when it's hot there is less O2 because more of it has been used. So while I did not explain the actual way a O2 sensor works correctly I did explain what is happening with the exhaust temp correctly. The hotter it is the more air that was used in the explosion.
    You can get to a point where not only are you risking valves and pistions your over heating the cat and you can get hot enough to melt the inside.
    Yes that is correct that it can go back to open loop and get on a pre determined fuel map. Simple low hp engine usualy use the non heated version. they are MUCH cheaper. The High HP engine where detonation and other problems are more prevelent will use the heated versions to get real time data at a earlier point so that they can go close loop and avoid any mixture problems that could damage the engine. With the emmissions being tighter and tighter you will probably see more cars go to the heated version so they can drop their higher warm up emmissions when running open loop. They have already gone to multiple O2's this gives the computer a way to verify that the primary O2 is working correctly. If the computer see's 2 different reading from the 2 O2's (ro some run 4! 2 per side of the motor) it percives a problem and throws a code. It may even get to the point that you will see 1 per cylinder so that it can real time each cylinder.
    I recently ran into a problem with my Supra. I had 1 injector go way lean. Well since the O2 was down stream and measuring all the cylinders exhaust that one cylinder raised the exhaust temp/ lowered the O2 content. The computer percieved a lean condition and richend up the mix on ALL the cylinders. Of course the bad injector stayed the same. My economy dropped because 5 of 6 cylinders were running rich. I was also getting major drop in power in mid range when the knock sensor picked up the detonation on that one cylinder and backed out of the timming. Finnaly it burnt the exhaust valve and I figured out the problem the hard way.
    Now if you really want to get into it the leaner the more power. 14.5:1 is regarded as the perfect mix for gas. the reason is that it the point where you can control the fuel burn the best with regards to the thermo limits we have with cooling and the metals we use. If you could run the octane way up and make the engine able to deal with the heat you could run a leaner mix and have less emmsions. However Detonation becomes a real problem and you have a hard time controling it. You also have a hard time getting rid of that much heat. SO the end result is what we regard as the perfect mix for gasoline to get the best bang without damaging the engine.
    Good catch on the O2 sensor operation.

    I don't need no damn shop manual, I got a pornographic memory.
    <a target="_blank" href=http://communities.msn.com/OffroadK5s>communities.msn.com/OffroadK5s</a>
    75 Jimmy, Dollar
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  8. Pure Insanity

    Pure Insanity 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    I cant decide if I am more educated or more confused now! THANKS GUYS! [​IMG]

    I get all the exercise I need pushing my luck! [​IMG]
     
  9. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    Right about now I wish I had fule injection! I bought the truck as a rolling chassis. No nothing but 10-bolts and tires.

    Do you know someone selling a BBC fuel injection setup? I would love to make that upgrade one day...

    <font color=red>Just give me a tank, and point me in the right direction!</font color=red>
    <font color=blue>DONT MESS WITH AMERICA!</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s
     
  10. Burbinator

    Burbinator 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    WOW. I just had the basics of theory, now I have the whole shooting match on the EGR. Thanks for the info!

    - Alan

    '82 K10 Suburban Silverado (AKA U.S.S. Nimitz)

    Terrorists are good for one thing...FERTILIZER

    GOD BLESS AMERICA!
     
  11. mike reeh

    mike reeh 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    egr valve on a carbureted vehicle is soley for emissions.. I would block it off if at all possible.. computer controlled egr is really the only way to accurately control detonation and NOx emissions w/o compromising driveability, and economy, etc.. Even on a tbi setup I'd get rid of the ESC distributor and block off the EGR valve, if I had my choice.. it really doesnt help ANYTHING.. the only time removal can hinder performance is if the rest of the intake/engine control system is designed and calibrated for the use of EGR.. thats my $0.03

    mike
     
  12. TorkDSR

    TorkDSR 1/2 ton status

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    too many words in this forum for only a half dozen posts. it's like reading the sunday paper, i don't read the comics with a lot of words, but the words i read are interesting and to the point!

    Tork DSR
    I just got a winch, it takes the fun out of things.
    http://www.torkpig.homestead.com<P ID="edit"><FONT class="small">Edited by TorkDSR on 09/25/01 10:02 PM.</FONT></P>
     
  13. Burbinator

    Burbinator 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    Considering that my truck operates in an emissions control city (Phoenix), the removal or disabling of the EGR isn't an option. As long as my overall performance is fairly good, I can hang with keeping the Smog Nazis happy. If it ever gets to the point where it just won't pass anymore, I'll be registering it in another county or considering a newer Sub. Info appreciated!

    - Alan

    '82 K10 Suburban Silverado (AKA U.S.S. Nimitz)

    Terrorists are good for one thing...FERTILIZER

    GOD BLESS AMERICA!
     
  14. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: GIVE THAT MAN A TROPHY!

    I wonder why GM was putting EGR's on 327's back on the 1964 engine I have in my 70 Burb....yes it's original. Hmmm I guess it has nothing to do with the 62cc double hump heads and high compression then. Sure was an emmision issue back in 64. I guess Delorian and the boys had it all wrong.

    I don't need no damn shop manual, I got a pornographic memory.
    <a target="_blank" href=http://communities.msn.com/OffroadK5s>communities.msn.com/OffroadK5s</a>
    75 Jimmy, Dollar
    Grim-Reaper
     
  15. Executioner

    Executioner 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    Good post ! Will they understand ?
    We can only hope so.
     
  16. Burbinator

    Burbinator 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    That comment is borderline inappropriate, implying that someone lacks the mental capacity to comprehend an explanation that was so eloquently explained by Grim. Not all of us are experts, hence this forum and its plethora of questions and answers. Knowledge is power, my friend, and the learning curve a toll road: ride with someone who has already paid.

    - Alan

    '82 K10 Suburban Silverado (AKA U.S.S. Nimitz)

    Terrorists are good for one thing...FERTILIZER

    GOD BLESS AMERICA!
     
  17. Executioner

    Executioner 1/2 ton status

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    Re: GIVE THAT MAN A TROPHY!

    Sorry if you toke it the wrong way. Can you speak for the other posters who don't have a clue ?
    The post was ment for them to open up and smell the EGR, and other emmisinions components !
     
  18. Burbinator

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    Re: GIVE THAT MAN A TROPHY!

    I'm not trying to spark up a debate. I just think that all of us here have something to contribute to each other and to imply that someone is not the"sharpest tool" might discourage people from asking questions or answering a post. I think that would be a disservice to us all. Don't you? No harm, no foul, it's all good.
    I will agree on this, though : Some people should keep their hoods shut.

    Sorry, Doc, didn't mean to intrude on your post.

    - Alan

    '82 K10 Suburban Silverado (AKA U.S.S. Nimitz)

    Always do sober what you said you'd do drunk. That will teach you to keep your mouth shut!
     

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