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Diagnosing Vacuum Hose issue

Discussion in 'LR4' started by Chrisarobin, Nov 23, 2020.

  1. Chrisarobin

    Chrisarobin Member

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    My LR4 has over 214k miles and has been regularly serviced. I even did the water pump ( couple times) and they replaced the coolant lines that are known to leak.

    I am hearing a faint whistle from under the hood (closer to the passenger side up in back like near the battery) that is more evident as you turn the car off and it continues like 2 seconds after the engine stops. What could this be? I can try to record it and post the audio here. in terms of performance: the vehicle runs fine however at idle it seems to wavier slightly around 900 - not as smooth as it typically is. is this something serviceable / DIY or should it go into the shop? tried searching but didn't see any other similar threads.
     
  2. Michael Gain

    Michael Gain Full Access Member

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    Smoke testing would best, but you can improvise with soapy water, a tissue, or some other smoke source. Sounds like the vacuum line that connects to manifold. I would let it idle and and take some incense, or a punk stick, and trace the line. See if any of the smoke is drawn into the line that way.

    Hope that helps!
     
  3. scott schmerge

    scott schmerge Full Access Member

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    like Michael says, smoke test will reveal leak.

    My guess is your pcv valves on the back passenger side valve cover. They sit right next to the battery box on top of the valve cover (two circular disk looking things on the V8- I think it’s only one on the v6). You should get a too lean code though if you have a big leak. May be the start of something. The pcv valves are cheap (~ $30) and a 10 minute job. Just make sure you don’t do like I did and snap the brittle valve cover tabs that hold the pcv valve in place.

    photo below.

    7C10B588-68CD-44F8-BEDC-BF0B2AF116B1.jpeg
     
    Last edited: Nov 24, 2020
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  4. Chrisarobin

    Chrisarobin Member

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    Thank you for posting this - I will check it out today. may be easiest just to replace both and see if that does the trick. I don't have a code reader but would this issue trigger the check engine light? it definitely is not idling correct.
     
  5. Chrisarobin

    Chrisarobin Member

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    thank you - just curious where this location is you are referencing? if it is closed is this something the average non Meccanic could fix DIY?
     
  6. Michael Gain

    Michael Gain Full Access Member

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    It would let you know which part to replace vice replacing everything. The vacuum lines are not cheap ($30-50 a piece).

    I can second @scott schmerge . Also, the noise you are describing sounds like it is bleeding vacuum upon shutdown. It's normal to equalize, but it sounds like a leak.

    Along the passenger side, in between the air intake and engine, and battery compartment and engine, there is a long, sectioned vacuum line that runs from the vacuum pump to the intake manifold. I would trace this line:
    Screenshot_20201129-101549.jpg Screenshot_20201129-102107.jpg Screenshot_20201129-102254.jpg
    It may look a little different on the 5.0, but same concept--vacuum line tracing from vacuum pump to intake manifold.

    Also, do the PCV valve diaphragms as Scott suggested. If you have a length of vacuum hose sitting around, push one end into your ear and use the other end to listen for air noises. The shorter you can safely make it, the better it will work.

    Hope that helps!
     
  7. scott schmerge

    scott schmerge Full Access Member

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    Depends on how bad your leak is...if it’s just the beginning of a leak, it may idle poorly but not throw a code. If the leak worsens, you’ll get a pending code and then a code. My money is on the diaphragms of the pcv valve. These are items that wear over time, failing at about 75-125k miles. The hoses are less likely to fail unless you’ve done recent work or someone was in there and accidentally knocked/broke one. If you go get incense and hold close to the leak or you can carefully spray brake cleaner (it will stutter when you spray on the leak as the cleaner is sucked in).

    I’d spray on The pcv first and see... then move to the hoses if that doesn’t yield results.

    let us know what you find.
     
  8. jlglr4

    jlglr4 Full Access Member

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    Just to pile on the suggestions - check the vent lines from the valve covers as well as the PCV valves. I highlighted the areas in green on Michael’s photo. There are two. One on the driver’s side valve cover that connects directly to the air intake (I’ve had this one pop off when I didn’t connect it properly). The other (passenger side) leads from the PCV valve and connects to the throttle body. I assume these are the same on the 5.0, but I have a 3.0.

    But I agree with the others that it sounds like the PCV membrane starting to go. Mine made a sound somewhere between a whistle and a moan that I could only hear right after I shut the engine down. I first thought it was a pulley going bad. C4BEF993-7781-4EFA-A626-C59C35C70493.jpeg
     
  9. BeemerNut

    BeemerNut Full Access Member

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    Attach a vacuum pump to the engine while not running and hunt down the vacuum leak noise location.
    Years ago it was the brake vacuum booster failing problem with a large enough vacuum leak causing a rough (ruff) idling condition.....~~=o&o>.......
     
  10. Chrisarobin

    Chrisarobin Member

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    Thank you everyone for you support here. I purchased 2 PCV valves from Amazon. Removed the old ones carefully (warmed the car up first to ensure the plastic would have some flex. Yup, both had a minor tear. Replaced them both in a few moments and tested it out. Car idles better and doesn’t whistle down the road anymore. Again, after 230k miles this was a refreshing DIY opportunity. Thanks for the help everyone.
     
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