never ending vacuum switch problem

Discussion in 'The Garage' started by Big GMC truck, Jan 11, 2006.

  1. Big GMC truck

    Big GMC truck Registered Member

    Aug 23, 2005
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    1984 gmc k1500 305
    My heat riser was rattling, so I replaced the vacuum switch that controls it. After replacing it with a new one, the heat riser still rattles. When I disconnect the vacuum line from the heat riser, the rattle stops. With the engine fully warmed up, I'm getting 14 pounds of vacuum from the line controling the heat riser.:confused: Instead of getting 14 pounds, I should get none. Does anyone know what could cause this? Thanks
  2. BIG*RED

    BIG*RED 1/2 ton status

    Mar 14, 2003
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    I am assuming that you are refering to the efe valve that is inbetween your exhaust manifold, and exhaust pipe. passenger this correct?

    If so, mine rattled also, because it was just worn out (the buttferfly valve inside of it)

    If you are getting vaccume on it, after it has warmed, you could have a faulty valve, or you could have the wrong tvs (thermostatic vaccume switch) there are several different ones available, each one has a different color on the top of it, and each color has a different temp. that it operates at.

    Now the best way I found to solve all of this was to :

    1. Remove the efe valve from the truck.
    2. Take a hammer a chisel and knock the butterfly valve out. (or weld the butterfly in the open position, i chose to remove it)
    3. Re-install the eve valve between the exhaust manifold and exhaust pipe

    This way, A: you don't get a rattle, and
    B: when you go to get it smoged, it still passes visual inspection

    (they can't see inside your pipe to notice that the butterfly is missing)

    and as long as you let the truck warm up before you head to the smog station, no one will ever know, and it won't affect your smog outcome..( i passed smog inspection twice with it set up this way on mine)

    Of course the absolute best way, is to move to a place where they don't require you to smog your vechicle, and just remove all that junk from your engine..thats what i did:wink1:
  3. diesel4me

    diesel4me 1 ton status Premium Member

    Jul 24, 2003
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    wrong switch..

    I've done what Sheldonblaze said (about "gutting" the EFE "butterfly" and replacing it so it appears stock)..but here where I live,its best to leave it in place and operational,especially if you have an aftermarket carb like a Holley or Edlelbrock with any spacers or adapters under them..the carbs frost up and sweat,and the vehicle runs like ca-ca and stalls at every stoplight,or when you try coasting!..nearly gets you killed when the motor stalls,and power steering and brakes dissapear!:eek1: ..happens often in foggy or cool damp weather,when its under 50 degrees..

    Since your in CA though,you probably wouldn't notice much difference,that is,IF your in the warmer parts of the state..I'd either fix it right,or do like what was suggested,so the "visual" inspection wont be an issue..

    You probably have either the wrong ported vacuum switch,(PVS)or are hooking the EFE up to the wrong ports on the right one..the EFE's PVS is located in the thermostat housing..there is another PVS in the intake manifold right next to it,that one is for the EGR valve,and works just the opposite of the one for the denies vacuum when cold,and allows it when the coolant warms up enough...the PVS for the EFE ALLOWS vacuum cold,and denies it when hot!..

    The same PVS for the EFE,is often tied in with the distributor vacuum advance,the switch has several "ports" so both the EFE and vacuum advance can plug onto the same switch..if you put the vacuum hose for the EFE o the ports intended for the distributor advance,it might do what you are describing too..have to use the vacuum gauge to find which port gets vacuum only when cold!..and make sure the right port on the PVS is hooked to the MANIFOLD vacuum source(one that has suction at idle!)...

    Despite being called a "ported vacuum" switch..most of them use MANIFOLD vacuum to "energize" them!..confused yet??:doah: ....and aren't emission controls a blessing to work on??:surepal: :mad1: ....

    P.S.. if it still "rattles" after your sure everything is getting vacuum only when its supposed to,you can insert a "vacuum delay valve" that acts as a "snubber"in the vacuum hose to the EFE,so the EFE wont "chatter" like that..even a perfectly normal one will rattle a few times when the PVS starts to open as the coolant hits the right temparature..I had one that used to make me think a rod was about to come thru the block every morning!.. :(

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