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Thread: Vacuum?

  1. #1
    Join Date
    Feb 2016
    Location
    Utah
    Posts
    1

    Default Vacuum?

    I recently replaced the freeze plugs on my 99 Cherokee Sport 4.0.

    Once I had everything back in place I started it up and it immediately ran up to the redline and I shut it down. Checked everything and tried again. Same result.

    I loosened up the intake to make sure I had it on the guide posts. Everything appears to be in the proper place and torqued in the proper sequence.

    Today I had a friend with me and when I started it we could hear a vacuum leak at the rear of the engine. I have a new manifold gasket and we both inspected it and everything seems to be sealed properly.

    Could a vacuum leak in one of the lines cause the engine to rev to the max?

    Would resetting the PCM do anything?

    RSWiser

  2. #2
    Join Date
    Sep 2009
    Location
    Chico, CA
    Posts
    29,847

    Default Re: Vacuum?

    That is a big vacuum leak. Did you leave the brake booster line loose? Is the butterfly in the throttle body seated?
    230 hp 4.3L Chevy
    Built 4L60E with manual lockout
    Atlas 4 speed
    Griffin radiator
    On board air
    Warn 9.5ti on custom bumper
    7.5" RE front and bastard pack rear on custom long arms
    30 gal gas tank
    lockers
    And a bunch of other stuff

  3. #3
    Join Date
    Mar 2009
    Location
    Katy, Texas
    Posts
    27,332

    Default Re: Vacuum?

    I can't wrap my head around this. The butterfly would have to be open, probably wide open to hit 5k rpm.

  4. #4
    Join Date
    Oct 2011
    Location
    S.E. Texas
    Posts
    29,260

    Default Re: Vacuum?

    Left my booster vacuum off one time and it only went to 2500~. I'd suspect that new gasket or something holding the throttle open like mentioned above.

    Also, just as a precaution double check all the sensors are connected and didn't get damaged.

    Sent via messenger pigeon. I talk, he types.
    Last edited by XJ Wheeler; 02-16-2016 at 08:13 PM.

  5. #5
    Join Date
    Jan 2012
    Location
    Oregon
    Posts
    2,489

    Default Re: Vacuum?

    I'm wondering if the TPS (throttle position sensor) is jacked up.
    5" lift, 33's. Armored, Lighted, Chipped, & Locked up Front. Soon to come: winch, gears, axle shafts, and more...
    Built Not Bought - Senior Member
    TheVoiceofJosh.com/

  6. #6
    Join Date
    Oct 2011
    Location
    S.E. Texas
    Posts
    29,260

    Default Re: Vacuum?

    If you unplug the tps the rpms would change if it was the source right? If so, worth a shot for free!

    Sent via messenger pigeon. I talk, he types.

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