Vacuum gauge wildly fluctuating

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  • Retro93
    Junk Collector
    • Nov 02, 2001
    • 2850
    #1

    Vacuum gauge wildly fluctuating

    The needle on 3 different gauges fluctuates so rapidly that all you see is a blur at around 10 in/hg
    When I bring engine speed up to around 2k I can see the blur disappear, but the needle is still jumping around. The highest vacuum reading I've seen is around17"/ mercury. What's up with this? This engine has around 15k miles on a garage rebuild. Bad valve springs?
    79 Cherokee Chief WT "RDBLOK" warmed over 360, TH400/QT, 4.10 Truetrac F/Detroit Locker R, 4" Skyjacker Softride System, Rancho 9000 shocks with in cab adjust, Hydroboost brakes, 33" BFG Mud Terrains
    Tags: None
  • babywag
    out of order
    • Jun 08, 2005
    • 10288
    #2
    Check PCV valve...
    My '90 did that with vacuum gauge.
    On investigations under hood my PCV valve was buzzing.
    Replaced the cheapnese pos and gauge was then normal.

    Might not be your issue but worth a shot.
    Tony
    88 GW, 67 J3000, 07 Magnum SRT8

    Comment

    • Retro93
      Junk Collector
      • Nov 02, 2001
      • 2850
      #3
      This is happening to an engine that I rebuilt around 20 years ago. From day one there has been a problem with the vacuum reading. Over the yrs I've changed cams/lifters/intake manifolds etc. None of the changes affected the vacuum readings.
      79 Cherokee Chief WT "RDBLOK" warmed over 360, TH400/QT, 4.10 Truetrac F/Detroit Locker R, 4" Skyjacker Softride System, Rancho 9000 shocks with in cab adjust, Hydroboost brakes, 33" BFG Mud Terrains

      Comment

      • babywag
        out of order
        • Jun 08, 2005
        • 10288
        #4
        Well then sounds like valvetrain...
        Were the guides checked when you rebuilt it?
        Tony
        88 GW, 67 J3000, 07 Magnum SRT8

        Comment

        • Retro93
          Junk Collector
          • Nov 02, 2001
          • 2850
          #5
          They were nurled. I'm thinking about having them replaced. Any idea what a fair price for a guide would be?
          79 Cherokee Chief WT "RDBLOK" warmed over 360, TH400/QT, 4.10 Truetrac F/Detroit Locker R, 4" Skyjacker Softride System, Rancho 9000 shocks with in cab adjust, Hydroboost brakes, 33" BFG Mud Terrains

          Comment

          • babywag
            out of order
            • Jun 08, 2005
            • 10288
            #6
            varies by shop & location.
            here where I live in socal head work is very expensive (I think)
            only couple shops close by and they got everybody by balls and charge more than other areas.
            local shop here said ballpark $250 per head or $150 for bronze liners
            I could drive couple hours away and still save some $$.
            best to call around and see
            Tony
            88 GW, 67 J3000, 07 Magnum SRT8

            Comment

            • Ristow
              • Jan 20, 2006
              • 17292
              #7
              I’d say you have a burnt valve or a valve not seating otherwise. Could be a busted spring but I doubt it if it’s done it since it was assembled. It could be a botched knurled guide. I didn’t think anyone actually did the knurl thing, it’s not a good fix.
              Originally posted by Hankrod
              Ristows right.................again,


              Originally posted by Fasts79Chief
              ... like the little 'you know what's' that you are.


              Originally posted by Fasts79Chief
              I LOVE how Ristow has stolen my comment about him ... "Quoted" it ... and made himself famous for being an ***hole to people. Hahahahahahahahahha!

              It's like you're unraveling a big cable-knit sweater that someone keeps knitting...and knitting...and knitting...and knitting...

              Comment

              • wiley-moeracing
                350 Buick
                • Feb 15, 2010
                • 1430
                #8
                agree, usually a valve issue when the needle fluctuates.

                Comment

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