1st Gen R53 Cooper S Most liked posts in thread: NEED HELP figuring out low vacuum issue! Feel like I've tried everything....

  1. Dave.0

    Dave.0 Helix & RMW Powered
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    #13 Dave.0, Dec 20, 2015
    Hoping you are not using something like Alta silicone intercooler boots. OEM rubber boots seal best.

    Also, take off your intercooler, seal off one end and fill it with water. If it leaks you have found your issue. I had a corner rub and tiny hole developed over time. I cleaned the I/C with degreaser and JB welded the hole to seal it.

    Later I picked up a GP I/C just because.
     
  2. silence238554

    silence238554 New Member

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    #7 silence238554, Dec 12, 2015
    I think you may have just nailed it-

    I just back probed my MAP & TMAP sensors. What I'm mainly wondering is - What is considered "out of spec"? How off from the OEM spec should a sensor read before replacing? These are the measurements I took vs. Bentley spec.

    I have hi lighted the values from my sensors that I feel may be problematic-

    Pin1/Pin2/Pin3/Pin4

    MAP (Key On, Engine Off)
    0.0/NA/4.99/4.06
    (Idle)
    0.0/NA/5/2.4

    TMAP (KOEO)
    0.0/1.31/5/1.95
    (Idle)
    0.0/1.3/5/1.12

    Bentley-
    MAP (KOEO)
    0.0/NA/5/4
    (Idle)
    0.0/NA/5/1.8

    TMAP (KOEO)
    0.0/3.9/5/1.90
    (Idle)
    0.0/1.25/5/0.9
     
  3. nkfry

    nkfry New Member
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    #12 nkfry, Dec 19, 2015
    The MAP sensor and brake booster line aren't under boost, they are under vacuum (as is the rest of the system until you accelerate and create boost instead of vacuum), so the soapy water solution isn't going to show any leaks. You will need to either pull the intake tract apart again and inspect everything or find a shop that is proficient in finding such pesky leaks.
     
  4. Canusrufis

    Canusrufis RMW Powered R53
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    #2 Canusrufis, Dec 9, 2015
    are you putting the green gasket on the SC inlet first then the inlet tube jammed onto the green gasket? I'm sure you are but want to confirm.
     
  5. Canusrufis

    Canusrufis RMW Powered R53
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    #3 Canusrufis, Dec 9, 2015
    and boost gauge is in "vacuum" at idle right?
     
  6. minimark

    minimark Well-Known Member

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    #4 minimark, Dec 9, 2015
    Smoke test it.
     
  7. silence238554

    silence238554 New Member

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    #5 silence238554, Dec 12, 2015
    Correct, on the SC first, seated completely.

    Yup, boost gauge is in Vacuum, but not enough vacuum. Should read at 15 in HG, mine hovers around 10, fluctuating back & forth depending on how warm the engine is (suspect wherever the leak is is contracting / expanding).

    Did this, they didn't find anything. After realizing that smoke machines only pressurize to about 1 psi, that's when I bought an air compressor & rigged up my own pressure tester.
     
  8. ScottinBend

    ScottinBend Space Cowboy
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    #6 ScottinBend, Dec 12, 2015
    MAP sensors?
     
  9. silence238554

    silence238554 New Member

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    #8 silence238554, Dec 15, 2015
    Hmm.... well, just swapped in a set of known good sensors & the car runs exactly the same.... So..... any other thoughts?
     
  10. nkfry

    nkfry New Member
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    #9 nkfry, Dec 17, 2015
    Are your intercooler boots seated properly and not tucked under the clamps?

    Is the engine in time?

    Check the MAP sensor source from the black tube, as some people have broken the gray line that goes to the MAP sensor and have similar issues.
     
  11. quikmni

    quikmni Moderator

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    #10 quikmni, Dec 18, 2015
    I had a problem with the gray line not sealing properly at the end. The line was not cracked or broken but must have leaked slightly depending on the engine movement. Smoke test could not find leak. I replaced Ox and MAP sensors but still infrequent error code. I finally replaced the line and all is well. I suspect when I replaced the line it sealed better at one of the ends, I think at the Supercharger end.
     
  12. silence238554

    silence238554 New Member

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    #11 silence238554, Dec 18, 2015
    Yup, intercooler boots are seated properly. when pressurizing the intake system I made sure to soak them with soapy water to look for bubbles & they didn't show anything.

    The engine is for sure in time. When I did the head gasket, I second guessed myself on the position of the timing marks so I pulled the timing cover & lined up the links & everything.

    I sprayed that MAP sensor line with soapy water as much as I could but it's pretty difficult to see where it seats down into the black intake pipe.

    Interestingly, the car has started running perfectly on occasion once it's had time to warm up. It doesn't always do this, but it seems possible that if there is a leak, once it's warmed up the material expands, seals itself and allows the car to pull proper vacuum. Reads at 15 in Hg, idle falls to a solid 800 RPM, everything. Unfortunately, it doesn't last very long. I'll go out to drive it the next day & it starts / idles like crap again.:mad2: