vacuum advance testing

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by txbluethunder, Feb 15, 2002.

  1. txbluethunder

    txbluethunder 1/2 ton status

    Jan 29, 2002
    Likes Received:
    Austin, TX
    does anyone know how to test the functionality of the vaccum advance on the distributor. i don't think mine is advancing (popcorn machine at anything above idle) and i'd like to test it somehow.
    also, i cannot get it to idle at 8 degrees like it says on the specs. it stalls at anything below ~16 degrees. i've already replaced the cap, rotor, wires, plugs & pcv valve.
    all help is appricated!

    1986 K5 Blazer
    Tired Stock 305/700R4/3.08
    F:2.5" Procomp Springs/RS9000
    R:1.5" Procomp Leaf/2" Procomp Block/RS9000
    Working on getting 33's
  2. Thunder

    Thunder 3/4 ton status

    Jul 20, 2000
    Likes Received:
    Northeast Nevada
    Are the plug wires on right. ? Check the fireing order.
    A Bad vacume advance usually wont cause popping unless maby its stuck at full advance even then its duobtful. But usually the return spring pushes it back to static timing(8 deg). vacume advance is only really a fuel saving device it only workes when the engine in under high vacume. Like when crusing down the freeway. It advances the timing to get the best MPG. Under acceleration it does not work at all.
    Your engine should run ok without it even being hooked up.
    Its possible that your mechanical advance is bad or a spring poped off of the weights. That can cause it to be fully advanced at idle. The mecanical advance is located under the rotor.
    Your distributor may also be a tooth off.
    Timing gears worn???
    Just some ideas.

    <a target="_blank" href=> Blazer pics</a>

    <font color=blue>Nevada... Where the pavement ends and the west begins
  3. weisel

    weisel 1/2 ton status

    Feb 22, 2001
    Likes Received:
    Laveen, AZ
    My vacume advance went out on me about a month ago. What went wrong with mine is the little vacume diaphram got a leak and the dang thing never advanced. Disconect your vacume line going to the distributor. Hook up three vacume lines to one of those "T" junction thingies. Hook one up to a vacume guage, one up to the vacume advance on the distributor, and pull a vacume on the other one. I just sucked on it with my mouth, then put a pair of vice grips on the one I sucked on (to seal it off). Then just look at the vacume guage and see if the vacume advance is holding a vacume. When I did mine, the vacume dropped really quickly and almost made me think I was doing something wrong, but I got a new vacume advance assembly, and it held a good vacume.

    No, thats not a dent in my truck's body. I call it my truck's armor.
  4. mdm365

    mdm365 1/2 ton status

    Jul 2, 2001
    Likes Received:
    mineral wells wv
    First off check the firing order starting on#1in the rotation of the dist(clockwise)If you find that to be correct look for vacume leaks that will cause the no idle situation.<a target="_blank" href=http://mikes77k5blazer>my k5</a>

    1977 k5-blazer4"pro comp lift 3.5 in rear dana 44,12 bolt rear, 350 &,205 t-case,465 trans,flotech headers and mufflers

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