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Vacuum System

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Innerpiece, Jan 4, 2002.

  1. Innerpiece

    Innerpiece 1/2 ton status

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    Hi all --

    Well -- I'm starting to realize that the fool that had the blazer before me boogered quite a few things up. 1987 silverado K5, TBI 305, 700R4 Raptor, NP 208, corp 10 bolt, 32" tires. It's still doing some odd things ("vacuum advance seems to work sometimes, other times doesn't, throws a code sometimes, etc). I have some trouble shooting to do to decide if its bad components, bad wiring, or bad installation ... So here are a few questions:

    (1) Where can I find a vacuum system diagram?

    (2) Where can I find details of how the "Computer Equipment" is hooked up to the vacuum system (i.e. for the "vacuum advance" component, the vacuum line goes to this port, this port is open to the ambient air, the electronic "input" is 12V to this wire, ground to this wire, the "output" should be this many volts at this pressure (or ohms), etc.)

    Thanks in advance!
     
  2. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    The stock TBI systems do not have a vacuum advance. The advance is controlled by the computer. If I remeber correctly the MAP sensor ( Manifold absolute pressure) is located on a bracket next to the the throttle body and It should have a vacuum hose that goes to the base of the throttle body. Get a Hayens manual for 15 bucks. I found the 88-91 manaul had much more info. on the TBI system than the 74-87 manual.
    Good luck.

    Mike
     
  3. Innerpiece

    Innerpiece 1/2 ton status

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    yeah -- it's not the standard thingy mechanically linked to the distributor ... but there is a component that adjusts spark timing based on the manifold pressure (effectively a vacuum advance component) ... it's that (and the other ecm components on the motor) that I need good info on (this hose goes here, this wire does this etc)

    ... good info on the later model haynes book though ... thanks!
     
  4. TwoCrowsDesign

    TwoCrowsDesign 1/2 ton status

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    There's some pretty good information at the following links:
    http://www.goingfaster.com/spo/electronic_engine_management_sys.html

    He's got info on the site on v6 as well as 305/350, but the ECM stuff is almost identical.

    The Helm manuals are the best in this regard, as they are in general, but pricey at around $100 for the set. <a target="_blank" href=http://www.helminc.com/helm/homepage.asp>http://www.helminc.com/helm/homepage.asp</a>

    Good luck


    John
     
  5. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    Yup, get the manual. You can do some limited diagnostics with a voltmeter but beyond that you really need a computer scanner. I pick up an auto x-ray on ebay for 80 bucks. It's well worth the investment if you plan to keep the truck and work on it yourself. With it I learned how EFI works and had fun doing it. So much so I took off the TBI and put on a TPI system but thats another story.
     

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