EGR Valve differences?

Discussion in 'Engine Topic' started by Michael211_2000, May 23, 2011.

  1. Michael211_2000

    Michael211_2000 New Member

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    Apr 16, 2011
    North Houston, Texas
    What is the difference from 1 EGR Valve to the next? I'm looking at 2 different EGR Valves for my 1978 Camaro Z28 (w/Federal emissions package): an SMP/Standard EGV323 and an SMP/Standard EGV324. They both look identical from their pics, but 1 is listed for a 1978 Camaro LT Coupe 5.7L engine and the other for a 1978 Camaro Z/28 Coupe 5.7L engine.

    What could possibly be different between these 2 valves?

    I'm taking a chance and placing an order for the EGV323 EGR valve (which was the one listed for a Z28). It just bugs me that they look identical (and exactly like the old frozen EGR valve I have here in my hands I need to replace, mounting wise). :confused:

    Does an EGR valve work off of exhaust temperature as well as engine vacuum (from the EGR TVS switch) or just off of engine vacuum? How do these valves actually work.... anybody?

    Thanks!

    - Michael
     
  2. Damon

    Damon Veteran Member

    12,937
    21
    Nov 16, 2000
    Philly area
    There are slight differences based on exhaust backpressure (but not temperature). One is probably a negative pressure valve the other a positive pressure valve. Or perhaps just a difference in how much vacuum it takes to open them fully. It's a little beyond me exactly what that means but it mostly gives fits to the EFI guys who sometimes get Check Engine lights after changing the valve for the wrong kind. For earlier non-computer controlled engines it doesn't seem to make much difference.
     
  3. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

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    Jun 11, 2002
    Northern VA
    Just vacuum, so far as I know.

    - EGR TVS keeps it from opening at all, until the engine is warm enough.
    - vacuum is connected to a ported source on the carb. No vacuum at idle keeps the valve shut, then it pops open once you tip in to part throttle.
    - At full throttle, vacuum disappears, so valve shuts.

    That's the basics. As Damon mentioned, the different parts of that era had different vacuum calibrations, but that's about it, I think. LT vs. Z28 would have different exhaust systems, thus different backpressure, thus different amounts of exhaust gas recirc'd back to the intake. Between the LT and Z28 pieces for a 5.7, I would guess the difference is something you'd only pick up on an emissions sniffer, but that's just a guess.
     
  4. 79ZED

    79ZED Veteran Member

    3,054
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    Jan 31, 2000
    Nanaimo, B.C., Canada
    There were three types of EGR valves used in the late seventies:

    Ported signal - used a ported source from the carb to control EGR flow

    Positive Back pressure - used ported signal and amount of positive exhaust back pressure to control flow. Most Federal, CA, and High Alt cars.

    Negative Back Pressure - Same idea as positive but used negative back pressure to control flow. Used on Z28's.

    They all looked much the same on the outside.

    John
     
  5. JordanZ28

    JordanZ28 New Member

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    Dec 26, 2017
    Can you update the part number for the z28.
    Thanks
     
  6. 79ZED

    79ZED Veteran Member

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    Jan 31, 2000
    Nanaimo, B.C., Canada
    Jordan,
    Personally , I would have went for the Z28 one, but I doubt it will make a difference between pass or fail on an emission test ( if you have one ). GM parts book lists 17052669 for a 78 Z with manual trans. The original part number that was stamped on the valve should be 17503034 if you still have it. The auto trans version is listed as 17052714, with the original stamped as 7043133. Trying to get an exact replacement might be tough.

    John
     
  7. JordanZ28

    JordanZ28 New Member

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    Dec 26, 2017
    Thanks for replying, is there a difference if I put auto transmission EGR on manual . Or the other way around.
     
  8. budro6968

    budro6968 Veteran Member

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    Apr 2, 2016
    Jax Florida
  9. 79ZED

    79ZED Veteran Member

    3,054
    5
    Jan 31, 2000
    Nanaimo, B.C., Canada
    JordanZ28,
    The 78 F body with an auto is listed as part # 17052714, original part was stamped 17052307. I'm sure there was a slight difference between the two ( otherwise GM wouldn't go to the trouble to have sperate part numbers ), But I doubt it makes a big difference, as I stated before. Budro6968 idea to soak them in carb cleaner or some other solution should work, just check to make sure the vacuum diaphram isn't leaking first.

    John
     
  10. JordanZ28

    JordanZ28 New Member

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    Dec 26, 2017
    Thanks for replying and your time I will give it a go and see what happens.
     

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