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  1. #1
    Legend

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    Default Looking for someone to school me on- Vacuum Lines

    Ok, I've gotten to the point where I've push out a few more childhood memories so that means I have room for more stuff!

    I'm curious to know if anyone feels like educating those that may not know (like me!) about vacuum lines in regards to GM trucks. Questions I'm curious about are things like..


    • What do vacuum lines do, in general?
    • How many lines are we talking about here?
    • Are they something that can be changed out while doing maintenance in order to prevent future troubles?
    • What is the reasoning behind checking for leaks by spraying something like an aerosol?
    • Are vacuum lines all pretty much part of one system, or do several different systems use vacuum lines?


    Anything else we should all know about vacuum lines?
    Steven



    "The Sarge"
    1999 Chevy Suburban LT- K2500
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  2. #2

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    I'll give you a quick explanation. Older cars had miles of vacuum lines as they were used to control just about everything. Nowadays we're seeing less and less vacuum lines. The vacuum comes from negative pressure <vacuum> caused by the piston on the intake stroke. This vacuum is available most of the time the engine is running at idle and deceleration. It can be stored in a tank for the times your engine is under a load because at that time there is no vacuum. The vacuum is used to help apply your brakes, move blend doors inside your dashboard to control the cabin temperature, suck fumes out of your crankcase, operate your cruise control, open and close your EGR valve and hot air intake to your air cleaner.
    I'm sure someone else will chime in here but basically that's what vacuum does. Vacuum lines should remain soft if they are rubber and should be replaced when they get hard before they crack. Same with plastic lines.
    A vacuum leak will cause your engine to run lean which is BAD. A lean condition can cause engine damage. Your computer will do what it can to correct the problem when it senses vacuum leak. It can only enrich your fuel mixture and set a lean code.
    Jim

    2004 SILVERADO 2500HD LS
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  3. #3
    Master Mechanic Dr_Zero's Avatar
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    Default

    Jimmiee did a good summary but I will add my .02 cents

    * What do vacuum lines do, in general? They suck

    * How many lines are we talking about here? Can be several from tiny ones to large ones that go to your brake booster.

    * Are they something that can be changed out while doing maintenance in order to prevent future troubles?
    Sure you can! is pretty easy you just slip the old one of and slip on the new just be sure to do only one at a time if you get them mixed up it can be a pain

    * What is the reasoning behind checking for leaks by spraying something like an aerosol? If you spray and there is a change in the way the engine is idling then you found the area where the hose is taking in outside air.

    * Are vacuum lines all pretty much part of one system, or do several different systems use vacuum lines?
    Well yes and no vacuum lines are all part of the vacuum system and this can entail lines going all over the engine especially on the older cars. In the shop manuals it has a wiring diagram and a vacuum diagram kinda like the human body has 2 circulatory systems one pumps blood around and the other moves lymph around.

    Bet ya didnt think I could tie these two subjects together LOL
    http://www.lymphnotes.com/article.php/id/150/
    My trucks!

    1996 GMC Suburban SLT
    1997 GMC Yukon SLT

  4. #4
    Legend bry2500's Avatar
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    Default

    That Pretty much covers most of your questions. The best thing to know about vacuum lines is that if you have to remove them for any reason TAKE A PICTURE FIRST. I know from experience. My Avalanche has 2 but I had the opportunity to rebuild a Ford escort engine in auto shop tech and we didn't take any pictures. It took us 3 days to get the vacuum lines back in right. There had to be about 100 feet of vacuum line in the little engine. It went everywhere like spider webs. I always kept a polaroid camera around because of that lesson learned. Now with cell phones and digital cameras it is alot easier to have a camera readily available.
    BRYAN

    "IF YOU DON'T TREAT IT LIKE A TRUCK IT'S JUST A REALLY BIG CAR"

    02' Avalanche 2500 Onyx Black
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  5. #5
    Legend

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    Default

    So no matter what they control, cruise, egr... they all go TO the engine, right? Which is why if it's a vacuum line and it's got a leak, it will affect idle if you spray aerosol in the right place.

    Thanks for all the great input. I'm sure I won't be the only one to enjoy learning this stuff.

  6. #6
    Master Mechanic Dr_Zero's Avatar
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    Default

    Quote Originally Posted by Springthing View Post
    So no matter what they control, cruise, egr... they all go TO the engine, right? Which is why if it's a vacuum line and it's got a leak, it will affect idle if you spray aerosol in the right place.

    Thanks for all the great input. I'm sure I won't be the only one to enjoy learning this stuff.
    Yes pretty much they do they might run all over and through stuff but eventually there is something going to the engine.

    Here is a old school fellow talking about vacuum you might like
    http://www.theautoist.com/vacuum_guage.htm

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