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Thread: Whistling during acceleration

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    Whistling during acceleration

    I did a search, found some threads that were somewhat similar, but not exactly the same as what I'm experiencing, so I'm starting my own.

    At highway speeds, I have a distinct whistling/whining sound during acceleration. I'm not positive where it's coming from. Sometimes I'm sure it's from the rear, sometimes I'm positive it's coming from the front right, sometimes, I think it's coming from the engine.

    If I take my foot off the gas, even though I'm pretty much going the same speed, it goes away completely. If I then put my foot on the gas and give some gas, but not the same amount, it makes the sound, only quieter. I can tap my foot on the gas and make the sound turn on/off in time with my tapping.

    Any ideas?
    1985 2wd Toyota Van

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    Re: Whistling during acceleration

    .


    ......try humming instead?

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    Re: Whistling during acceleration

    Bump
    1985 2wd Toyota Van

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    Re: Whistling during acceleration

    I have met a few vehicles that whistle at highway speed, in all those cases its been wind entering the body envelope (usually around the windscreen but not always)
    But those sounds are generally specific to a particular speed &/or crosswinds and generally not dependant upon accel/deccel conditions.

    Your's sounds more like it is only occurring when the engine is under load (and at speed)

    My first thought would be a vacuum leak of some sort.
    But I would probably start with taking a very close look at the LF engine mount.

    As the engine spins, it wants to torque in the chassis towards the passenger side, the engine mounts are there to restrain that motion and transmit the power to the chassis. When the LF mount fails, it allows the engine to twist significantly in the chassis, straining everything thats attached to the motor.
    I replaced my mounts for other reasons, but did find a lot of other strange behaviours and noises disappeared, all at the same time.

    Noises are the hardest to diagnose, especially when they're intermittent or only at high speed.
    Perhaps having a helper move around in the van while you create the noise, might help to pin down where the noise is emanating from and narrow your scope of investigation.

    For what it's worth, diffs and tranny's usually make noises on deceleration (when they are not under load).
    Belts/idlers and alternators can produce "whistling" type noises but will generally do so at all speeds under load (not just at high speed)

    Good luck, let us know what you find out.
    BB

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    Re: Whistling during acceleration

    thanks Burntboot.
    the van is running so well I'd be tempted to just ignore it if I could.
    I like the idea of a helper moving around to help pin point it. I'd thought of that myself, then forgot. Maybe your reminder will help me get it done.
    The fact that it only happens at a certain speed (high speed at that) leads me to think it is wind rushing into or over something.i agree that it seems it would be there all the time if it were a bearing or the diff or trans.
    1985 2wd Toyota Van

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    Re: Whistling during acceleration

    I had this and it ended up being a warped exhaust manifold. Different engine, but worth looking at.

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    Re: Whistling during acceleration

    Besides the annoyance of the whistle, whats the down side of ignoring a warped exhaust manifold? what did you have to do to fix your problem?

    Also, yours was %100 dependent on the gas peddle being engaged? I don't understand how I can let my foot off the gas and it completely disappears, returns the instant I give it gas. Seems like it's got to be tied to the throttle?

    I'm not arguing. I'm way to ignorant on the subject to argue. i'm just trying to understand.
    1985 2wd Toyota Van

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    Re: Whistling during acceleration

    Yeah mine only whistled when I was on the throttle. It was the exhaust leaking between the engine head and exhaust manifold. I removed the manifold and put a straight edge across and it was warped quite a bit, about .040" end to end. I took it to a machinist and had him machine it flat. Working good now.

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    Re: Whistling during acceleration

    It's not an uncommon problem for the Previa to develop a whistle from the exhaust. I've seen this three times and in all cases it was the muffler. Toyota did a wonderful job on Previa exhaust systems (stainless steel). This means the exhaust system lasts almost forever. Most Previas are old enough now to have needed a muffler replaced 2 or 3 times, but due to the stainless steel construction are still on their 1st one. Although the exteriors hold up very well, not all the internal baffles do. In some cases (random) the baffles corrode in such a way as to create a whistle. It comes on gradual at 1st and only occurs while under full load (highway speeds and/or driving up hills). Over time it will usually get worse. Eventually it will whistle all the time and becomes easy to identify (at least it did with mine).

    Since this issue is random (only happens to some), and since the mufflers will otherwise last for a very long time, rather than spend a bunch of $$$, I went to a salvage yard and got a used muffler. If I remember right it cost me around $40. That was about 30k miles/10 years ago & still no whistle. FYI, the Previa muffler has a long pipe attached to it from the factory. At the end of that pipe there is a flange with 2 bolts. It's easy to replace yourself (no cutting or welding) if you get a OE muffler. Even a used OE will likely be better than a new one from an exhaust shop (the Previa I took mine from had around 300k miles on it). If you go to an exhaust shop, they will likely just cut the old muffler off the stock pipe, then weld a standard muffler in it's place. If you go that route, I'd expect it to last only about 5 or 6 years. Tim

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