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Thread: What is this Vacuum line?

  1. #1
    Join Date
    Jul 2012
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    Question What is this Vacuum line?

    Heya guys hows it goin?

    So for a while now I have been wondering what this particular vacuum line is and what its function is, and is it crucial to the idle? I have noticed that if I remove this hose the idle will get all lopey and it will run rough! And if you look closely it looks as if its spewing out oil or fuel or something to attract all that dirt? And should this hose be so loose that I can pull it off with my fingers? I have read online about it being a "crosstalk hose" or bypasss hose" or whatever but I want to know for sure because it is quite loose! Now mind you the loose part is only the end I pulled off in the picture, the other end of the same hose is not loose, which seems odd to me. Also is there a better alternative to this rubber hose? I have read about braided hoses and diff brass fittings? Anyway to sum up all this text I am new to this I am the rookie and you guys are the veterans! I look forward to discussing this thanks!

    Zach




  2. #2
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    Can't say for sure why your car seems to run rough without it. I deleted this line and capped each end on two of my cars but they were tuned afterwards. Either way, my recommendation to you is to replace the hose if it is loose with one that seals tight. On my modified cars i zip-tie every vacuum line to help ensure they are sealed. Braided line is overkill for vaccum lines, it just looks better but costs a lot.

    Go around and make sure all of your vacuum lines seal nice and tight, if not replace them.

    Chris
    Me-89 SC 5-speed 1.7 Autorotor twin screw over 443rwhp 20psi
    Her-95 SC auto 1.7 KB 400rwhp 17psi
    my email

  3. #3
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    Thanks Chris! I will be sure to ask if I have any other questions. It is greatly appreciated.

  4. #4
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    I hope somebody can answer a question for me. where does that other vacume line to the right go to. I've had it capped off since I put my motor back in because I just couldn't find where it goes.
    1991 SC 5spd
    1979 F-250 4x4 SC(Supercab) 400 4bbl 8spd
    1988 18' Checkmate Exciter 225 Evinrude 24p Chopper

  5. #5
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    Quote Originally Posted by SCEnthuzy View Post
    Thanks Chris! I will be sure to ask if I have any other questions. It is greatly appreciated.
    I just responded to your other post regarding your stalling issue. Oddly enough I diagnosed your stalling issue as a vacuum leak then read this. I am even more convinced you have a vacuum leak. I would pul a page out of the Dave Neibert book. I would replace all of the old loose oil soaked rubber hoses with new ones then use two zip ties on each end to insure they are tight.

  6. #6
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    Thank you 90sc35thann. I suspected that hose! What is the David Neilbert bert book you refer to? And I am just curious as to the way things work, if its a vacuum leak why would it clear up when the engine is revved? because the engine is sucking in air more?

    Thanks,

    Zach

  7. #7
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    Because when you rev it the computer throws more fuel and probably compensating for running lean. Dave Neibert is a club member here and if I recall he advocates for using a couple of zip ties on each vacuum connection to insure a good seal.

  8. #8
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    Quote Originally Posted by 90sc35thann View Post
    Because when you rev it the computer throws more fuel and probably compensating for running lean. Dave Neibert is a club member here and if I recall he advocates for using a couple of zip ties on each vacuum connection to insure a good seal.
    I do advocate the use of zip ties on all vacuum hose connections, but only one per connection.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat...............707HP/650TQ

    My Garage

  9. #9
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    Quote Originally Posted by SmokinTbirdSC View Post
    I hope somebody can answer a question for me. where does that other vacume line to the right go to. I've had it capped off since I put my motor back in because I just couldn't find where it goes.
    Goes to the cruise control.

  10. #10
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    Mar 2009
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    Greenville, North Carolina
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    Thanks. It was so tight back there I just couldn't find a vacume line. That has been bugging me every time opened my hood. You made my day.
    1991 SC 5spd
    1979 F-250 4x4 SC(Supercab) 400 4bbl 8spd
    1988 18' Checkmate Exciter 225 Evinrude 24p Chopper

  11. #11
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    That line you colored green goes to the PCV vale located at the rear of the R valve cover. In case you still want to know. Concur with the previous advise. Find al loose vacuum lines and replace them. Tie them as well. Then if it still idles crappy ( other post) seal the intercooler tubes.
    90 5 speed. Owned since 4-91 it had 12,000 mi. Motor out since '99. I'm gonna fix it, really. Hoping for 450+ HP
    95 auto. owned since 03. Now a Daily driver the motor is in. It continues with electrical gremlins. I think in the PCM harness. Will be a daily driver. Expect 300 to 350 HP

  12. #12
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    Quote Originally Posted by SCEnthuzy View Post
    Thank you 90sc35thann. I suspected that hose! What is the David Neilbert bert book you refer to? And I am just curious as to the way things work, if its a vacuum leak why would it clear up when the engine is revved? because the engine is sucking in air more?

    Thanks,

    Zach
    Yes, basically, that's it. Just to make it really conceptual and basic, if the engine is sucking in 10 units of air through the leaky hose, and 5 units of air through the IAC valve and throttle body, then the car is getting way, way more air than it wants. But when you rev the engine up, the engine may be pulling 30 units of air through the throttle body, and still only 10 units through the leaky hose. So by revving the engine up, it went from 300% as much air as demanded to only 133% as much. That extra 33% is much easier to manage than an extra 200%.

    Once you replace that crosstalk hose, you will pick up some extra maximum boost as well. It leaks boost as well as vacuum.
    Last edited by S_Mazza; 01-16-2013 at 12:10 PM.
    God bless!!!

    1990 SC auto ... red outside, gray cloth inside ... ~205,000 miles (and climbing) ... driven daily!

  13. #13
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    The only issue I had when deleting the cross talk hose, was that the bypass valve became super sensitive and would close with even the slightest load on the motor or press of the gas pedal, which caused the supercharger to be under a load and whine constantly.

    In my case I didn't notice a change in max boost, with or without the cross talk hose, so after a couple weeks I put it back on.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat...............707HP/650TQ

    My Garage

  14. #14
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    Quote Originally Posted by David Neibert View Post
    In my case I didn't notice a change in max boost, with or without the cross talk hose, so after a couple weeks I put it back on.
    I may have been a little unclear. I meant that in the case of my car, I picked up boost that had been lost to atmosphere when the cross-talk hose was leaking.
    God bless!!!

    1990 SC auto ... red outside, gray cloth inside ... ~205,000 miles (and climbing) ... driven daily!

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