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Thread: EGR Problems

  1. #1
    Jr. Apprentice revscott's Avatar
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    Default EGR Problems

    I have a 88 C1500 5.7 TBI

    I was experiencing rough idle and bad hesitation at take off. I replaced plugs (bosch +4 platinum), wires, rotor, dist cap all to no avail. I replaced the egr and the egr solenoid also no change. While checking for vacuum leak, i broke one of the plastic hoses to the egr solenoid. I drove the truck to autozone with the hose off, the truck ran GREAT. When I replaced the hose the problem came back. I currently have the hose unplugged with a little fuel filter stuck in it to help filter the air intake. the truck runs good, but I get a light at hwy speeds. Switch off and back on, no light. I would like to give it a proper and permanent fix however. Any suggestions would be greatly appreciated.

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    Typically Bosch do not do well with our rides. A/C Delco is the highly recommended brand/type.

    Check out this thread, especially post #s 18 thru #20 is they speak specifically about late 80s.

    http://www.gmtruckclub.com/forum/sho...ighlight=bosch
    Last edited by mfleetwood; 03-21-2012 at 07:51 AM.


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  3. #3

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    Quote Originally Posted by revscott View Post
    I have a 88 C1500 5.7 TBI

    I replaced plugs (bosch +4 platinum), wires, rotor, dist cap all to no avail.
    There's yer problem! Bosch plugs are made for Euro cars! What wires/cap and button did you use? If not AC/Delco, rip 'em off and try again.

    About your problem, I am having a similar one. I don't think that it is all about the Bosch plugs since I have DELCO in mine. I get the same CEL at highway speed. My next test is going to be fuel pressure.
    "It went together didn't it? Well then there has to be a way to take it apart!" - Me.

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  4. #4
    Jr. Apprentice revscott's Avatar
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    I had all of that tested, checked out good. Its definitely an egr problem but I can't figure it out. The egr is not even engaged at idle but if the hose is plugged to it, it has rough idle and hesitation. Its puzzling me!

    ---------- Post added at 01:46 PM ---------- Previous post was at 01:14 PM ----------

    It is firing well, this thing pulls like a russian race horse! Its just when the egr vacuum hose is plugged in that it has the rough idle (like a misfire) and bad hesitation. I have changed the egr, gone back and cleaned the tubes out a second time. Changed the egr vacuum solenoid and replaced the vacuum hoses from the intake to the solenoid and from the solenoid to the egr. ??????? Its driving me nuts. New parts should equal change in performance! But it hasnt.

  5. #5

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    Almost sounds to me like the control source "telling" the egr to open is acting up and activating it when it shouldn't be.
    2010 Silverado LT 1500 5.3L 4X4
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  6. #6

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    I have a 93 w/ the 5.7l and am experiencing the same problem. Mine is a tad bit different with the hesitation still happening with the egr silenoid vacuum hose disconnected, but it is not as bad as having it hooked up. I took out my egr to check if it was working properly, no problems there. I think that we need to check the IAC or other sensors. The chiltons states the egr silenoid gets a input from the the computer based on the out put of three other sensors. I don't have the book with me right now to pull up the correct verbage.

  7. #7
    Jr. Apprentice revscott's Avatar
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    Quote Originally Posted by Scott_Anderson View Post
    Almost sounds to me like the control source "telling" the egr to open is acting up and activating it when it shouldn't be.
    Thanks Scott, any suggested fix or replacement?
    The Rev

  8. #8

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    I know it's not ideal, but I drove my '91 for five years and several thousand miles with the EGR hose disconnected and plugged with no problems at all. If yours affects the idle, then you need to test the EGR control system, most likely you have a faulty EGR control solenoid. But if you're a poor country preacher like me, and can live with the light on, just drive it.
    Good Luck and God Bless
    Remember that if you're not part of the solution, then you're part of the problem!

  9. #9

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    Found this on another site, it is a pretty thorough write up.
    The most common EGR system failure on our trucks is the valve itself; the diaphragm fails so the EGR valve will not open. You can eliminate this possibility right off the bat by testing the valve with a vacuum tester (Mityvac.) Shut the engine off and connect the tester directly to the EGR valve. Pull vacuum (around 15 inches is plenty) and be sure it holds for a minimum of 20 seconds. If it does not build or hold vacuum, the valve could be held open by a chunk of carbon, which you could attempt to clean out – but most likely, the valve is bad and needs to be replaced.

    If the valve passes the hold test - with vacuum still showing as holding on the tester, have a helper start the engine while you watch the gauge. The vacuum should bleed off immediately.

    Determine whether the EGR passages in the intake are clogged by carefully depressing the EGR diaphragm with your fingers. Take care to not burn your fingers or get them caught in the openings under the EGR. When you press the diaphragm, the engine should stumble noticeably, and possibly stall. If there is little or no response, the passages in the intake are likely clogged with carbon. Effective cleaning of these passages requires removal of the intake manifold.

    Check the vacuum source to the EGR solenoid. Connect a vacuum tester (Mityvac) to the line leading from the TBI unit to the front (single port) side of the solenoid. There should be full vacuum at idle, around 20 inches/Hg on a stock engine. If not, remove the line from the TBI and connect the tester directly to the TBI to verify vacuum. If none, the port itself may be clogged.

    Reconnect the line from the TBI to the solenoid and move the tester to the line exiting the rear of the solenoid. At idle there should be NO vacuum reading (be sure you purged your gauge if necessary so that it reads zero before connecting.) Snapping the throttle should show some activity on the gauge as the solenoid briefly commands the EGR open.

    With the meter set on ohms, you can test the EGR solenoid coil across the two pins in the socket; any reading less than 20 ohms indicates a bad solenoid winding.

    With the meter set on DC voltage, or using a test light, check the EGR solenoid harness terminal A (pink/black) to ground. Key on, meter should read 12V or the test light should light up. Do not pierce the wire to test, simply unplug it and touch the test lead to the connector pin.

    Another possible failure that is difficult to test for is a weak spring inside the valve allowing it to open too easily. If you have exhausted all other efforts you may consider replacing the valve.

  10. #10
    Jr. Apprentice revscott's Avatar
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    Quote Originally Posted by Revredneck View Post
    I know it's not ideal, but I drove my '91 for five years and several thousand miles with the EGR hose disconnected and plugged with no problems at all. If yours affects the idle, then you need to test the EGR control system, most likely you have a faulty EGR control solenoid. But if you're a poor country preacher like me, and can live with the light on, just drive it.
    Good Luck and God Bless
    LOL Preacher! The poorest lol, I pastor a church in an area of alabama called Pigeon Creek! Made famous by the movie 'Sweet Home Alabama'. It doesnt effect the idle, just the light at highway speeds when the egr would kick in. Just worried that it may be running too lean which could cause problems. In the city it runs great.
    The Rev

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