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Vaccum leak??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by eshorvath, Oct 10, 2002.

  1. eshorvath

    eshorvath 1/2 ton status

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    I am having a little back fire rumble at accelleration. I cannot figure out if it is a leak causing it, or running lean, or a vaccum leak causing to run lean???????? Or what??
    I found a small oil leak at the manifold to engine block seal in the rear, could this oil leak from the oil gallery cause a vaccum leak??
    The project is SLOWLY getting better, just a few minor problems.
    Please help if you can.
    Eddie
     
  2. Muddytazz

    Muddytazz 1 ton status

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    Almost any vacuum leak will cause a engine to run bad since the vacuum comes off the engine. Oldest trick in the book is get a spray bottle full of soapy water and spray around hose connections and seals and see if the soapy water bubbles, if it does, you've got a leak.
     
  3. eshorvath

    eshorvath 1/2 ton status

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    I did that, and did not notice bubbles. I thought that was for a leaking tires anywayd, and was told to use either carb cleaner or starting fluid. When I sprayed the engine, I had a lot of boiling fluids on the hot engine.
     
  4. MNorby

    MNorby 3/4 ton status Premium Member GMOTM Winner

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    I spray carb cleaner all over the hoses and if the motor starts to run rougher or smoother than it was I know the leak is by where I just sprayed then pinpoint by spraying around that area
     
  5. eshorvath

    eshorvath 1/2 ton status

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    I only have one Vac advance line, one line for the power brakes and one for the Cruise control.
    Running an edelbrock carb and intake manifold. Bolts seem tight, I DO have an oil leak at the rear manifold seal...Maybe I needed to use more silicone...Will that oil leak cause a vaccum leak, even though it goes into the lifter gallery?
    Ed
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    No vac leak because of that. (or at least nothing that should affect engine operation)

    When I had a bad vac leak, there were a few symptoms, and all major. (1/4" vac line disconnected on a 400CID motor)

    First, at startup, the car would fire up, and die immediately. After that ONE stall, it would fire back up, and as long as it was on fast idle, it would run fine. Curb idle, in park, was VERY lopey. Putting it in gear (idle of course) would drop RPM's by about 300, and the car would tend to die, or at least sputter and shake. All problems ceased when RPM's were higher.
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Uhh to see the bubbles you would have to be inside the engine were the leak is. The bubble trick works good on pressurised stuff but on Vacuum it just suckes it in. /forums/images/graemlins/thumb.gif
    Carb cleaner of propane. Both will make the idle change when sucked into the engine.
     
  8. eshorvath

    eshorvath 1/2 ton status

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    I knew that fluids would be sucked into the engine with a vac leak, and bubbles would be if air was being pushed out, that is why people use starting fluid. The starting fluid gets sucked in, and causes the engine idle to surge, But...The problem is at HIGH vacuum conditions (accelleration) and I know that is IS NOT a word, but decelleration (accelleration in the opposite direction). So, spraying the engine vacuum areas with starting fluid at idle may very likely NOT work. I am repairing the leak in the back of the manifold, and will let you know if this helps... GOD, please let this work... If not, ANY ONE WANT A 1986 K-5?? CHEAP??
    Eddie
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    Did you mean to say acceleration isn't a high vacuum situation, and that the problem is occurring when there is high vacuum, deceleration? And yes, that is a word, I'm sure : )
     
  10. TXsizeK5

    TXsizeK5 1/2 ton status

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    I had what seemed to be a "vaccum problem" but it ended up being a faulty O2 sensor. Maybe thats it?
    Goodluck /forums/images/graemlins/thumb.gif
     
  11. eshorvath

    eshorvath 1/2 ton status

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    No Oxygen sensor on my truck. All the smog stuff fell off when I hit a big bump.
    Ed
     

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