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faulty egr valve

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by therover87, Jan 25, 2002.

  1. therover87

    therover87 1/2 ton status

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    I have an 87 k5 350 tbi and the other day i replaced the egr valve and it was running fine, it was idling probably better than it ever has since I got it, but yesterday the idle went back to the way it was, now the engine is surging the way it was before I replaced the egr valve, do you guys think that it is the egr valve, i spent 60 bucks on it so i might just go back and return this one.
     
  2. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Don't get me started on EGR problems.! [​IMG] [​IMG] I had the same problem and I thought it was EGR. So, I changed mine, returned "bad" EGRs, and generally wasted too many hours trying to figure out what was going on. I did learn allot about TBI in the process though. One thing I can tell you from painful experience. Check your fuel pressure FIRST!!! Mine was surging and running progressively worse over time. Turned out to be low fuel pressure. Go down and buy a $25-$35 in-line pressure gauge to mount under the hood. Look at it first if you ever notice problems. That's what all the tech resources suggest, check pressure BEFORE ANYTHING ELSE. Should be 9-12 psi (roughly, depending on the source). If the fuel pressure is ok, check vacume (or check it first, but you really need the gauge).

    I'm still new at this but I'm learning. The book "How to tune and modify Chevrolet Fuel Injection" was recommended to me and it is a great book to help you understand GM EFI, both TBI and TPI. If the fuel pressure and vacume are not the issue, there are many possible points of trouble that the book will explain to you and tell you how to test each component, usually with an inexpensive multi-meter or common tools.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked, 4" lift, 42" tires
    Some day: massive cutting, shorter wb and rear overhang.<P ID="edit"><FONT class="small">Edited by BadDog on 01/25/02 08:32 AM.</FONT></P>
     
  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Well first thing to understand is how, why and when a EGR is doing things. At idle the EGR will be closed. If it's open you will run like garbage! EGR will come on about 1500-1700 rpm. Now The EGR should be on a timmed port. Now on My Supra the device that contolled the timming gave it up. Start the car it would run fine. Drive down the road till the EGR activated and boom it idled like hell. Seems the check valve broke and it was not releasing the vac to the EGR once it went back to idle. So before you go blame the EGR there are other possiblility's.
    Now have you read the codes out of the computer? How old is the O2sensor? Bad O2 sensor could be running the truck rich and gumming up the EGR and holding it open. Stuck PCV valve can also cause run problems so start with the basics and see if you can find any other problems. Things like ignition problems like hung mechanical advance, plug wires's, bad water temp senso for the ECU not letting the FI to go into closed loop, etc.

    Women dig dents and flat paint!
    coloradok5.com/gallery/Grim
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    Grim-Reaper
     
  4. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Yep, EGR not sealing comes under the heading "vacume leak". It should only open under "cruise" (high vacume but above idle). And on the late 80's TBI, it is controled by the ECM providing ground to the EGR solenoid mouned over the pass valve cover. Oh, as far as I know, TBI doesn't use what I would call a mechanical advance.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked, 4" lift, 42" tires
    Some day: massive cutting, shorter wb and rear overhang.<P ID="edit"><FONT class="small">Edited by BadDog on 01/25/02 11:03 AM.</FONT></P>
     
  5. BlazinRojo

    BlazinRojo 1/2 ton status

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    I had an EGR valve stick open, so my car sucked all the time. Replacing it solved my idle problems. One word of advice though, the one from NAPA wasn't quite right....I went to the dealer to make sure I got the EXACT valve, not the generic one from NAPA. Has been beuatiful ever since....at idle at least.

    Shutup Brain or I'll stab you with a Q-Tip - Homer J. Simpson
     

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