CX Mystery Vacuum(?) Pump
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Thread: CX Mystery Vacuum(?) Pump

  1. #1
    Tadpole
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    Default CX Mystery Vacuum(?) Pump

    Hi all,

    After some time away I've come back to my CX, and finally decided to ask people who'd know, what this mystery item could be? (see photos)

    It looks like a vacuum pump, connected to the head just below the tappet cover, and no-where else. It's driven off the crank (via a really misaligned pulley which was tied off when I got the car). There may have been other connections in the past, it's clearly not been hooked up for a long time.

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    I've not seen this in any underbonnet pics before, and the car starts, runs, and does all it should without it running.

    Anyone have any ideas? Does it have something to do with the fast idle circuit? (as it's an early Cmatic car with A/C)

    Cheers,
    Mitch
    CX Mystery Vacuum(?) Pump-imag0115.jpgCX Mystery Vacuum(?) Pump-img_20180402_110938.jpgCX Mystery Vacuum(?) Pump-img_20180402_111132.jpg

  2. #2
    Fellow Frogger! Jinandfonic's Avatar
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    An Emissions control air pump. Most have been removed when the pump failed or pipe work rusted. It's used to increase the oxygen in the exhausts to lower the exhaust gases count. Still the same amount of pollution? Hopefully we never have to reinstate them....
    Citroen C5 II manual '05; C4 Exculsive '07; Citroen CX2200 Pallas '76; CX2400 C-matic Pallas '78

  3. #3
    1000+ Posts gerrypro's Avatar
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    I have mine in place for originality sake but the pump has been internally disabled and the pipes to the carb and to the exhaust manifold distribution plate have been blanked off! Looks according to the original specs but only there for appearance.
    Cheers Gerry

  4. #4
    Fellow Frogger!
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    Quote Originally Posted by Jinandfonic View Post
    An Emissions control air pump. Most have been removed when the pump failed or pipe work rusted. It's used to increase the oxygen in the exhausts to lower the exhaust gases count. Still the same amount of pollution? Hopefully we never have to reinstate them....


    All the pulleys and belts on a CX are driven from the camshaft not the crankshaft. The camshaft has an extra long "beak" that passes through the bell housing and all the pulleys are driven from that single power take off point.
    the camshaft is chain driven by the crankshaft by a sizeable shortish chain as it is a low mounted camshaft. The "timing cover" inside the wheel arch allows access to that vital but robust chain.
    As stated the additional air pump was a legislative requirement and was probably of little real value.

  5. #5
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    In old engines the air injection was indeed of value - it brought cat converters up to efficient temperature.

  6. #6
    Fellow Frogger! citroenthusiast's Avatar
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    Lucas vane pumps of the type shown in the photo, used for air injection, were notorious for failing. The sliding vanes would wear to the point that they would jam in the inlet slot causing the pump to seize.
    Cheers,
    John T.

    54 TAV Legere; 61DS19 LHM BVH (son's); 71DS21 BVH; 73SM 3.0; 73SM EFI (Megasquirt); 73SM 3.0 (other son's)

  7. #7
    Tadpole
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    Thanks for all of that guys, I was going to pull it off but wanted to double check it wasn't actually necessary. I'll yank everything out and blank off the ports (I'm not overly fussed on originality, the car's already had a few things done over the years).
    No idea if it's actually failed but don't think I'll bother finding out. Lucas strikes again!

    Interesting arrangement in that it wouldn't lower the actual emissions, but rather just the concentration of the nasties in the exhaust gases?

    My mistake fritzelhund, I forget that it's upside down in that respect (haven't actually touched the car in a while). Reminds me I should check out the condition of the chain...

    Cheers,
    Mitch

  8. #8
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    Air injection doesn't dilute the nasties - it burns (some of) them. Exhaust is initially hot but short of oxygen. Injection enables some combustion which also brings the converter to an efficient state.

  9. #9
    Tadpole
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    Interesting, brings back memories of high school science
    It's still getting the boot, but might wind up on the shelf instead of the bin

  10. #10
    1000+ Posts gerrypro's Avatar
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    Quote Originally Posted by seasink View Post
    Air injection doesn't dilute the nasties - it burns (some of) them. Exhaust is initially hot but short of oxygen. Injection enables some combustion which also brings the converter to an efficient state.
    That is odd! I have not yet seen a CX fitted with the air pump also fitted with a Cat Converter. Was this ever the case? I wonder!
    Jinandfonic likes this.
    Cheers Gerry

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