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Thread: Loud Hissing at High RPM

  1. 24th May 2013, 04:55 PM #1
    Davehillbo
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    Loud Hissing at High RPM

    Hi all. I have just acquired a 1989 range rover classic with an Isuzu 2.8 TD Conversion from a 3.5 vogue. Im having a few niggles although the truck drives well, and was hoping someone can help me out with it!

    Issue 1. When I put my foot to the floor in 2nd gear or above, at a certain point when its boosting (foot is far down), I will get a loud Hissing sound coming from left of the dash/engine , but if I let off ever so slightly it stops straight away, its like finding a balance before it hisses. Any ideas what this could be and how to fix it?

    Issue 2. Black smoke, I know its an old engine and im getting some black smoke when I boot it, is this normal? Many thanks. David.

    Ive included some pics of the engine bay to make things easier.

    David.



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  2. 24th May 2013, 05:09 PM #2
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    austastar
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    Quote Originally Posted by Davehillbo View Post
    I will get a loud Hissing sound coming from left of the dash/engine

    Ssssserpentine belt ?????


    No?


    cheers
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  3. 24th May 2013, 06:16 PM #3
    Davehillbo
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    Not the belt, its deffo air releasing somewhere, its like its blowing off, as I loose boost when it happens.
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  4. 24th May 2013, 07:50 PM #4
    Adrian18 Guest
    Air escaping from the intake post turbo maybe.. check intake manifold gasket and all connections back to the turbo ...maybe your loosing boost because its geting out and making a loud hissing noise .
    .. its happened to me
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  5. 24th May 2013, 07:56 PM #5
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    flagg
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    hissing + black smoke sounds like post turbo intake leak to me. Problem is you not be able to see it when it isn't on boost so it may not be obvious once you stop and lift the bonnet.
    Hercules: 1986 110 Isuzu 3.9 (4BD1-T)
    Brutus: 1969 109 ExMil 2a FFT (loved and lost)
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  6. 24th May 2013, 08:13 PM #6
    Davehillbo
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    The thing is, the turbo is on the other side of the engine, and it REALLY sounds like its coming from the other side. What is that thing in the middle of the manifold branch?
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  7. 24th May 2013, 08:25 PM #7
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    flagg
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    The inlet manifold is on the left though... maybe a gasket? What is the cylinder thing above where it bolts onto the head?

    Does it only happen under load or can you reproduce it while stationary? (you only get boost under load)
    Hercules: 1986 110 Isuzu 3.9 (4BD1-T)
    Brutus: 1969 109 ExMil 2a FFT (loved and lost)
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  8. 24th May 2013, 08:29 PM #8
    Davehillbo
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    only happens under load, its like it hisses at a set PSI, I can keep the throttle just under where it will hiss, Its like its set to hiss if that makes sense. I have no idea what the cylinder thing is, but it has a hole under it, so wondering if its blowing off through that?
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  9. 24th May 2013, 08:39 PM #9
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    flagg
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    If there is a hole all the time then that can't be good for your boost. If it is a whole in the cylinder then it could be a boost control device that stops it from over boosting.. do you have a boost gauge? I might not be operating correctly.
    Hercules: 1986 110 Isuzu 3.9 (4BD1-T)
    Brutus: 1969 109 ExMil 2a FFT (loved and lost)
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  10. 24th May 2013, 09:13 PM #10
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    steveG
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    Thing between the manifold branches looks like some sort of blowoff valve. Bet it's coming out of there. Tape a small plastic bag or rubber glove around it and take it for a drive. If it blows it off you will have confirmation.

    Steve
    1985 County - Isuzu 4bd1 with HX30W turbo, LT95, 255/85-16 KM2's
    1988 120 with rust and potential
    1999 300tdi 130 single cab - "stock as bro"
    2003 D2a Td5 - the boss's daily drive
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