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Hey Grim-Reaper EGR and Idle ??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Executioner, Mar 1, 2000.

  1. Executioner

    Executioner 1/2 ton status

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    I was under the impression that the egr does not function at idle ?
    Can you please explain ?
    Thanks alot
     
  2. Blazer79

    Blazer79 1/2 ton status

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    I'm not Grim-Reaper, so sorry to intrude here [​IMG]. From what I know, the EGR is connected to the 'timed vacuum port' on the carb. That means that vacuum is applied to the EGR valve until a certain acceleration is reached.

    When that acceleration is reached, the EGR valve receives vacuum and opens the exhaust recirculation passage on the intake manifold. If the EGR valve would open at idle, it would be a very rough idle.

    Hope this clears everything a bit, but I'm sure Grim Reaper will come and broaden it with the best explanation.

    <font color=purple>////////
    Go 79s!!!
    </font color=purple>[​IMG]
     
  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    It doesn't function at idle. it will make it idle rough. what it does is it slows the combustion process and reburns some of the fumes once the motor is under load. By slowing (perhaps controling is a better term) the combustion process it helps reduce ping. Once unleaded fuels came to be common place there was a problem with increased ping. The Lead in fuel helped control it as well as what usualy comes to mind is helped lubricate. Thats why in early and mid 70's trucks you will find many have to run a 4 deg timming mark to handle unleaded fuel or you have to run an additive, sometimes you will get away with a higher octane or octane addative.. I got ping so bad in my 75 I'm going to put a EGR on it once I come accross a carb thats right or come up with the money for FI. Right now it is such a dog that I can't even think about flooring it on a hill or it's ping central at 6 deg. mid grade is making it better but still not there. I could run the engine rich and hide the problem but I would be able to eliminate the ping problem at the cost of gas milage and no gain or a loss of power. The EGR will let me run a higher advance without the loss of economy. Most EGR's fail in the open posistion because of carbon deposits. Thats when you get the common bad idle problem that most people instantly reconize as a bad EGR. Now on the other hand a EGR stuck closed or say a leaking vac line. this manifest itself as a ping problem. Some people think they can gain power by disabling the egr..really it's a trade off yeah you may get a more powerfull fuel load but it's more likly to ping. From mid 80's GM was running Knock control devices so what happend is yeah you gained some High RPM Horse power by disabling the EGR but you loose some mid RPM torq under load because the Knock sensor is retarding the hell out of the timing to kill the ping. An example is a ping problem I chassed on my 79 before it got the crate. Damn thing started demanding octane boost to keep from pinging. So I start running bottle after bottle of fuel addatives thinking I got a carbon problem on the valvees and in the cumbustion chamber. Finnaly figured EGR is not working correctly or pluged. Slap a New EGR on it and difference. Well I finnaly blew a head gasket and thats when I found the problem. It was a carbon problem...in the intake. Seems carbon had been building in the port where the EGR dumps directly below the carb in the plennum devider. One side was slap plugged up and the other side was flowing a 1/4 of what it should have been. Never touched the timming cleaned out the port put the head gasket on it and the ping issue was gone. Actully ran the timming up to 10 deg from the 6 I was running and went fron 89 oct tane to 87 and had better power. Some of that gain was from removing a horriable carbon build up off the valves. When I saw how bad it was on the side with the blown gasket I puller the other head just so I could clean the valves.
    I asume this question was regarding a previous post about crate motors and the problem with the carb the guy has on the 75. well that carb doesn't have the delayed vac port and other fittings to run the EGR. you also don't want to run EGR till the engine is warmed up. Thats why the vac hoses are run through a thermal switch on the water neck.
    Ok I'll stop running on and hoggin disc space and boring you all [​IMG]

    Diging it in the dirt with my K5's
    Grim-Reaper
     
  4. delta9blazer

    delta9blazer 1/2 ton status

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    pretty smart, for an older guy

    wanna work on my truck?

    <font color=purple>delta9blazer</font color=purple>
     
  5. Waxer

    Waxer 1/2 ton status Author

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    Re: pretty smart, for an older guy

    Grim, come to Cali and help me out with my rig buddy..
     
  6. bigdaddy89

    bigdaddy89 1/2 ton status

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    Re: pretty smart, for an older guy

    Well Grim I think I have one for you. I have an 89 fi 350. Every time I let my rig sit long enough for it to get nice and cold it gives me problems as if I was running a carb on it. It will actually fall on it face as if it was getting no fuel for a second. I can let off the gas pedal and than king of pump it to get it going. It will do it for about the first 2 miles for only a couple times and than run like a bat out of hell any other time. What is the verdict. I forgot to add that I just did a complete tune-up 3000 miles ago. I am running a hypertech chip, 160 thermo, and a throttle body spacer. Help.
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    good loard how many days it take you to dig through this?

    it's your 160 thermostat. EFI needs a 190deg. With 160 it still running in open loop and running rich because it thinks it's still cold. It loads up and stalls. It finnaly builds enough heat to go closed loop after a couple miles. Normal summer operating temp on a EFI motor is about 200-210.
    The way the computer operates is it has a preset fuel map that is triggered when the temp is below a certain point. it then slowly ramps off the fuel mix as the temp comes up once it reaches a high enough temp it goes closed loop and starts using the O2 sensor to make it's fuel calculations. It's taking to long to get to that point with that 160deg thermostat. The engine is warm enough it doesn't need the extra fuel for cold start but not warm enough to tell the computer to go closed loop.

    Diging it in the dirt with my K5's
    Grim-Reaper
    <A target="_blank" HREF=http://grimsk5s.coloradok5.com/>http://grimsk5s.coloradok5.com/</A>
     
  8. Blue85

    Blue85 Troll Premium Member

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    Re: good loard how many days it take you to dig through this?

    If Hypertech is recommending a 160 T-stat, then their chip should be switching to closed loop at a lower temperature, no?

    <font color=blue>Powered by a Goodwrench 4-bolt longblock [​IMG]
    240hp...for now.</font color=blue>
     
  9. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: good loard how many days it take you to dig through this?

    Maybe, Maybe not. The rest of that computer and FI was designed with 190 in mind. The point it kicks into Closed Loop may have nothing to do with the Chip. That may be in the base computer. Also that chip is going to be a General chip. There are often small changes along the way and that chip may be a one size fits all sort of and not jiving with that computer.
    I was talking to my Cohort at work who is a FErd Gear head. Infact he's a ASE certified Mechanic. He actully saw that 160 as the issue before I did and pointed it out. He has played with some Hypertech stuff before and seen this issue. I Understand where there would be an issue. I really can't take the credit for the catch...I have to give that to my bud.
    We have a Hate Hate relationship hehehe He hate's GM I hate FErd LOL. Atleast he didn't get a Jeep. He got a scout LOL. Now he want's some advice on how to make it flex LOL He saw my truck off road and couldn't belive the stuff and droop I get. I walked some stuff sombody with a locker was all hung up on. He flipped when I told him I was open. Don't need no locker if you keep the tires on the ground [​IMG]

    Diging it in the dirt with my K5's
    Grim-Reaper
    <A target="_blank" HREF=http://grimsk5s.coloradok5.com/>http://grimsk5s.coloradok5.com/</A>
     
  10. tom

    tom 1/2 ton status

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    Re: good loard how many days it take you to dig through this?

    Great information on this post. Thank You! Iv'e got one. My stick shift '91 with TBI is awkward to drive because the RPM won't drop quickly beteen gears when shifting. Is there a good way to fix this? How about unpluging the idle air control? I live in a warm climate and I could just switch it in when needed on cold starts. Does this make any sense?
     
  11. bigdaddy89

    bigdaddy89 1/2 ton status

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    Re: good loard how many days it take you to dig through this?

    Grim, I kind of thought that is was the thermo, but wasn't for sure. I didn't start having the problem until it started getting colder. Hypertech says the reason for the colder thermo is to eliminate detonation. I am going to put my 175 back in and see if it clears up the problem. I appreciate the help with the problem.
     

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