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ECM / EGR Problem - ECM opening EGR solenoid way too early

This is a discussion on ECM / EGR Problem - ECM opening EGR solenoid way too early within the Technical / Maintenance forums, part of the General Discussion category; EDIT: Problem below resolved by new ACDelco EGR valve. Old EGR valve had weak spring making it open too easily, ...

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    ECM / EGR Problem - ECM opening EGR solenoid way too early


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    EDIT: Problem below resolved by new ACDelco EGR valve. Old EGR valve had weak spring making it open too easily, even though the solenoid was sending vacuum at take-off.


    Original Post:

    Hi guys... I have an EGR system issue: Hesitation on take-off mainly... related to EGR.

    1993 Chevy K2500 4x4 5.7L

    Behavior:
    Cool (or warm) engine, EGR solenoid is triggered, and opens EGR valve on take off, or does it off and on while holding RPMs steady around 2000 or so probably.

    With EGR valve disconnected or plugged, everything RUNS fine (but gives 32 code after 3 minutes on the highway)...

    I verified correct operation of the solenoid itself (it opens when triggered, and doesn't leak), and the EGR valve works fine. Vacuum lines are all good, and the system has good vacuum pressure when and where its supposed to.


    SO, my conclusion is that the ECM is sending the signal to activate the solenoid under the wrong conditions..

    my question is, what may be causing the ECM to open the EGR incorrectly, and what can i do to find the faulty part.

    Thanks all..
    Last edited by ninety6; 08-31-2010 at 08:32 PM.
    :: J o e y : :
    1993 Chevy K2500 | 350 A4 | red
    1965 Chevy Impala | 283 A2 [powerglide!] | orange
    2002 Chevy Camaro SS | 350 M6 | orange
    2005 Pontiac Grand Prix | 3.8 A4 | orange
    1999 Suzuki GSX-R750 | 749 M6 | red/black

  2. #2
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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    The ECM tests the egr valve at a steady cruise above 45mph. egr valve is most likely worn out. replace with oem.
    did you change anything in the ecm to make it send the wrong signal? if not its not the ecms fault.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    I didn't change anything -- but the truck has 121k on it when i got it. A previous owner had plugged the EGR valve (where the vacuum line connects) -- probably to eliminate the hesitation issue. I removed that plug, trying to get rid of the 32 engine code at highway speeds.

    the EGR valve functions properly (at least it seems to me). When the ECM sends the solenoid 12v to activate, the solenoid activates the vacuum, and the EGR opens up. when the 12v stops, the solenoid closes, and the EGR valve closes.

    Where does the ECM get its data for for knowing when to open the EGR?
    :: J o e y : :
    1993 Chevy K2500 | 350 A4 | red
    1965 Chevy Impala | 283 A2 [powerglide!] | orange
    2002 Chevy Camaro SS | 350 M6 | orange
    2005 Pontiac Grand Prix | 3.8 A4 | orange
    1999 Suzuki GSX-R750 | 749 M6 | red/black

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    the ecm has set tables it follows to control the egr valve when conditions are met(it actually switches it to ground to operate the selenoid. you have a negative back pressure egr valve effected by exhaust pressure on the other end. spring could be weak and keeping the valve open even though the ecm is commanding it closed.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
    Matching Ninja 500r


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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    I held my finger on it. It closes. It opens when the solenoid grounds (sorry i said 12v above, not what i meant) - and thats then the engine cuts out.

    i put a volt meter on and watch voltage on the solenoid, and when it triggers, volt meter picks up the voltage, vacuum activates, and EGR opens -- at the wrong time.

    if i pull off the vacuum line (or plug it), the valve closes, stays closed, and the engine runs like a champ.
    :: J o e y : :
    1993 Chevy K2500 | 350 A4 | red
    1965 Chevy Impala | 283 A2 [powerglide!] | orange
    2002 Chevy Camaro SS | 350 M6 | orange
    2005 Pontiac Grand Prix | 3.8 A4 | orange
    1999 Suzuki GSX-R750 | 749 M6 | red/black

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    enigne off apply vacuum to egr valve. use hand vac with guage.
    start engine valve should close and vacuum drops. if not egr is bad.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
    Matching Ninja 500r


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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    Quote Originally Posted by NEUMANNZZ View Post
    the ecm has set tables it follows to control the egr valve when conditions are met(it actually switches it to ground to operate the selenoid. you have a negative back pressure egr valve effected by exhaust pressure on the other end. spring could be weak and keeping the valve open even though the ecm is commanding it closed.
    my last sentence doesnt make any sense. should read: spring could be weak and keeping the valve open due to exhaust pressure.
    Last edited by NEUMANNZZ; 07-29-2010 at 08:27 PM.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
    Matching Ninja 500r


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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    I can check that, But why is the ECM triggering the solenoid to open the valve open just off-idle? is that normal?

    oh, and when i checked it manually (grounding the solenoid to open the valve), it opened fully when grounding, engine stumbled/died, and closed fully when taking it off ground (closing solenoid trigger), and engine ran smooth....

    thanks for the help!
    Last edited by ninety6; 07-29-2010 at 08:33 PM.
    :: J o e y : :
    1993 Chevy K2500 | 350 A4 | red
    1965 Chevy Impala | 283 A2 [powerglide!] | orange
    2002 Chevy Camaro SS | 350 M6 | orange
    2005 Pontiac Grand Prix | 3.8 A4 | orange
    1999 Suzuki GSX-R750 | 749 M6 | red/black

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    Not sure why ECM is opening it, if indeed it is or due to right conditions being met. You need to make sure the valve isnt opening prematurely due to exhaust pressure before you replace the ECM.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
    Matching Ninja 500r


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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    That is normal if it's a negative backpressure EGR valve. Don't buy a generic auto parts store EGR valve to replace it. Go to NAPA, or somewhere that sells AC Delco or Delphi, and get an OEM valve. That will make all things happy!
    Big E

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    FYI Update all:

    In addition to my sitting in the driveway diagnosis above:

    when driving, the EGR valve opens on take off, so the engine stumbles a little right on take off... or if just just barely press the gas to go really slow in a parking lot. Doesn't seem to matter if the engine is cold, cool, warm, or hot.

    Once disconnecting the electrical connector on the EGR solenoid, the truck runs like a champ again. The EGR does NOT open on its own, or due to exhaust backpressure. no stumble, no hesitation.

    This, to me, confirms again that the EGR valve itself is fine. it is only opening when instructed by the solenoid. The solenoid itself seems to be ok... as it opens activates/deactivates as instructed by the ground connection on the plug.


    So, i'm back to thinking it's an ECM problem... Unless there is something else that could send a "activate" signal to the solenoid...

    Further thoughts? Are there any sensors that tell the ECM its time to open the EGR?

    Thanks again
    Last edited by ninety6; 08-28-2010 at 12:48 PM.
    :: J o e y : :
    1993 Chevy K2500 | 350 A4 | red
    1965 Chevy Impala | 283 A2 [powerglide!] | orange
    2002 Chevy Camaro SS | 350 M6 | orange
    2005 Pontiac Grand Prix | 3.8 A4 | orange
    1999 Suzuki GSX-R750 | 749 M6 | red/black

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    Your troubleshooting efforts are good but not necessarily perfect for determining good/bad EGR valve. They can definitely get weak and open too easily. Measuring this is probably something only an engineer that worked for GM back in the day could tell you. Maybe someone knows how many inches in vacuum it should take to unseat the valve, but I've never seen these details.

    The #1 overwhelmingly common failure in this system is the EGR valve, and at 100K+ miles on the original, they're usually toast. I've found myself replacing bad ones on several vehicles that were just past 100K - my current '94 C2500LD 5.7, previous '94 Suburban 5.7, and several others. I like those two trucks as my best examples though because I bought them as one-owner vehicles and knew the service history, and knew the valves were original.

    A far-off #2 is the EGR solenoid itself, very few of them fail in comparison to EGR valve failures.

    I've never seen an ECM failure or other failure that causes the EGR valve to open at the wrong time. Not to say it's impossible, I just find it extremely improbable.

    I'll put $5 on bad EGR valve. As has been mentioned before, only replace it with an OEM one, do not be tempted by the cheapie parts house brand, or you may still have the problem after you've spent the time and effort. If the OEM valve does not fix the problem, replace the solenoid. You didn't waste any money on the OEM valve because at 100K+ it was ready to go anyway. Bank on that.

    Richard
    Last edited by someotherguy; 08-28-2010 at 01:02 PM.

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    Thanks..

    I have no issues replacing the EGR valve... my only issue is that i feel like something else is wrong --

    in driveway testing -- i put the a voltmeter on the solenoid. Each time the engine stumbled (b/c the EGR was opening), the meter showed 12v, indicating that the solenoid was telling the EGR to open. If the solenoid shouldn't activate outside of basically highway driving conditions -- why would the solenoid activate at just off idle, or at a 2k steady RPM in park? Or am i missing something about WHEN the solenoid should be activating. The EGR ONLY opens when the solenoid tells it to. UNLESS the solenoid had a variable vacuum control and isn't just off/on.

    There are no hesitation problems when the solenoid doesn't tell the EGR to open (confirmed via disconnecting solenoid electrical connector)

    so unless the the solenoid is supposed to briefly open when you hit the gas and/or butterfly at low steady rpm -- and my EGR is staying open too long b/c of loose spring, i don't get how its the EGR.

    I'm definitely not trying to negate anyone's opinions -- i guess i just don't get it! Thanks so much everyone, I really appreciate the troubleshooting help! We'll get it figured out!
    :: J o e y : :
    1993 Chevy K2500 | 350 A4 | red
    1965 Chevy Impala | 283 A2 [powerglide!] | orange
    2002 Chevy Camaro SS | 350 M6 | orange
    2005 Pontiac Grand Prix | 3.8 A4 | orange
    1999 Suzuki GSX-R750 | 749 M6 | red/black

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    Quote Originally Posted by ninety6 View Post
    so unless the the solenoid is supposed to briefly open when you hit the gas and/or butterfly at low steady rpm
    Yes, this is proper behavior. When you tip-in the throttle, the EGR opens briefly.

    The whole purpose of the EGR valve is to introduce inert gas (exhaust) into the combustion chamber to cool it down a little when under load. This is to prevent pinging. When the EGR is functioning properly, the ECM can command a more aggressive spark advance curve without risk of ping.

    If the EGR isn't opening (bad diaphragm, bad solenoid, passages blocked, vacuum disconnected, etc.) then the engine may ping, knock sensor picks it up, and the ECM dials back on the advance - costing power but hopefully saving the engine from damage.

    If the EGR is opening too easily or is stuck open (worn spring, wrong EGR valve, bad solenoid, carbon chunks on valve pintle or seat) then it adds the exhaust gas at inappropriate times, causing stumbling and poor drivability. A really bad or really incorrect one will make it seem like you have a crazy lumpy cam in the engine and can cause it to stall at transition from idle to partial throttle.

    I've experienced both failure modes personally, on a number of TBI trucks.

    Richard
    Last edited by someotherguy; 08-28-2010 at 01:29 PM.

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    aaah, thanks richard. i think that finally clears up some of my confusion. I'll go ahead and find me a new ACDelco EGR. It sounds like (based on that my solenoid IS operating properly) my EGR, though opening properly -- is staying open a little too long on the initial throttle or the low speed stead gas, instead of butterflying properly.


    Thanks all... I will update you after i get a new EGR valve in there...
    :: J o e y : :
    1993 Chevy K2500 | 350 A4 | red
    1965 Chevy Impala | 283 A2 [powerglide!] | orange
    2002 Chevy Camaro SS | 350 M6 | orange
    2005 Pontiac Grand Prix | 3.8 A4 | orange
    1999 Suzuki GSX-R750 | 749 M6 | red/black

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    I am having the same issue and have read a ton of posts with no actual answer. I've completely "tuned up" the truck as well as replaced the egr and the tps and I still get "bog" and stalls. I haven't run it without the egr solenoid unplugged to see if it clears up but I will try that. The issues continued even hours after installing a new egr and tps. I will say that there was a ton of build up in the old egr so maybe the manifold is my issue with additional blockage. Next I will try maybe a fuel pressure regulator. I've read that using a scanner tool not a code reader will pinpoint bad sensors. Oh and my truck kind of clears up when the additional strain of the a/c is turned off but not always.

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    Quote Originally Posted by Darkwing View Post
    I am having the same issue and have read a ton of posts with no actual answer. I've completely "tuned up" the truck as well as replaced the egr and the tps and I still get "bog" and stalls. I haven't run it without the egr solenoid unplugged to see if it clears up but I will try that. The issues continued even hours after installing a new egr and tps. I will say that there was a ton of build up in the old egr so maybe the manifold is my issue with additional blockage. Next I will try maybe a fuel pressure regulator. I've read that using a scanner tool not a code reader will pinpoint bad sensors. Oh and my truck kind of clears up when the additional strain of the a/c is turned off but not always.
    If you are not using the proper OEM Delco or Delphi valve (you did not mention), it will not function correctly. None of the parts stores (Advance, Auto Zone, OReillys) in my area carry the proper negative back pressure EGR valves in a AFTERMARKET brand. Delco or Delphi are the only valves that will make your TBI truck run correctly!
    Big E

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    It's an ac delco egr. I also didn't know ac delco started making their parts in china too. Boo.

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    Yes, unfortunately, it's the way things go. A lot of their fuel pumps are made there now too. Pretty soon we won't be able to buy any replacement parts that are worth a damn.

    Richard

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    Re: ECM / EGR Problem - ECM opening EGR solenoid way too early

    AND, take the part # from the top of the EGR valve with you. Buy it from a dealership,period. My experience has been that the part numbers have been updated a bunch of times. Also, does the EGR control solenoid have a filter? Its inside the round plastic cap that has vent slots in it, if it has one. If so, check for filter being packed with dust.

 

 
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