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  1. #1
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    Default Smog Pump makes rattling noise at idle, and when RPM's are dropping from reving motor

    1985 C4 (110,000 easy miles) - Smog Pump makes rattling/vibration noise at idle, and when RPM's are dropping down to an idle. Seems fine while driving. When the A/C is on, it seems louder/worse at idle (or dropping to an idle). I thought it was an internal vibration in the Smog Pump, or bad bearings so I replaced it. Problem is, the new one is just as bad. Does anyone know what can be making this rattling/vibration noise in the Smog Pump.

  2. #2
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    Quote Originally Posted by tigerdan View Post
    1985 C4 (110,000 easy miles) - Smog Pump makes rattling/vibration noise at idle, and when RPM's are dropping down to an idle. Seems fine while driving. When the A/C is on, it seems louder/worse at idle (or dropping to an idle). I thought it was an internal vibration in the Smog Pump, or bad bearings so I replaced it. Problem is, the new one is just as bad. Does anyone know what can be making this rattling/vibration noise in the Smog Pump.

    Are you 100% certain that it IS the smog pump? it could easily be the belt tensioner or water pump...even the altenator. If you use a section of 1/2" hose to listen to the pump and hold the end to your ear, you can clearly hear what is making noise.

    Smog pumps do require some break-in time. Its very easy to ruin one by getting it wet or trying to lube it.

    Once damaged it will eventually seize and leave you sitting there unable to drive.

    The mfg says 500 miles to break a new pump in. They might continue to whine after that, but a rattle or squeeking is a sign that its damaged internally.

  3. #3
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    Default It is the pump making the vibration/noise

    Quote Originally Posted by boomdriver View Post
    Are you 100% certain that it IS the smog pump? it could easily be the belt tensioner or water pump...even the altenator. If you use a section of 1/2" hose to listen to the pump and hold the end to your ear, you can clearly hear what is making noise.

    Smog pumps do require some break-in time. Its very easy to ruin one by getting it wet or trying to lube it.

    Once damaged it will eventually seize and leave you sitting there unable to drive.

    The mfg says 500 miles to break a new pump in. They might continue to whine after that, but a rattle or squeeking is a sign that its damaged internally.
    Thank you for the response... The noise is definitely from the Smog Pump area, and it is not a squeaking or purring noise typical of a normal pump if new. The tensioner was just replaced last week, the alternator is quiet, and the AC Compressor is not too old either. This is a new smog pump, but the noise/vibration is not a typical "new pump" noise. The noise is not there when the motor is above high idle (while driving), but when slowing down (about to stop) there is an intense vibration noise just before it drops to an idle. This is louder and vibrates more when the AC is on, but I think it is just the added strain on the belt drive system. With the hood open I can hear/feel the pump making this loud "brrrrr" vibration/noise. If I rev the motor it quiets down till I let off the throttle... when it drops almost to an idle and It will make the vibration/noise (and while it is idling).

    Question: Would anything with the Smog Pump air connection cause this problem? How is this checked out if so.

    Any help would be greatly appreciated, I thought a tensioner pulley would have fixed it, then went for the bigger $$ item and replaced the Smog Pump - but nothing changed.

  4. #4
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    Quote Originally Posted by tigerdan View Post
    Thank you for the response... The noise is definitely from the Smog Pump area, and it is not a squeaking or purring noise typical of a normal pump if new. The tensioner was just replaced last week, the alternator is quiet, and the AC Compressor is not too old either. This is a new smog pump, but the noise/vibration is not a typical "new pump" noise. The noise is not there when the motor is above high idle (while driving), but when slowing down (about to stop) there is an intense vibration noise just before it drops to an idle. This is louder and vibrates more when the AC is on, but I think it is just the added strain on the belt drive system. With the hood open I can hear/feel the pump making this loud "brrrrr" vibration/noise. If I rev the motor it quiets down till I let off the throttle... when it drops almost to an idle and It will make the vibration/noise (and while it is idling).

    Question: Would anything with the Smog Pump air connection cause this problem? How is this checked out if so.

    Any help would be greatly appreciated, I thought a tensioner pulley would have fixed it, then went for the bigger $$ item and replaced the Smog Pump - but nothing changed.
    Are you sure that it's not just a worn diverter valve cycling as it should?? They have been known to make a lot of noise on decel.
    The only thing that you accomplish when you make something idiotproof, is breed a better grade of idiot,
    Z06/Z16 #1689

  5. #5
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    I've also seen a PCValve that buzzed loudly at idle.
    The A.I.R. system supposedly makes strange noises without the "muffler" that hangs on the side of the water pump. Thats there to allow air to escape the system and to keep the noise down. I have no idea what they sound like without the muffler.

  6. #6
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    There is an actual vibration on the smog pump/mount support bracket when the noise is present. I am wondering if one of the air valves being bad would cause a "pressure" problem in the pump resulting in this noise. I will check for a worn diverter valve, thank you for the idea. Do you have an easy way of checking the air valves in this area, other than just replacing a them? Again, thank you everyone for the help here, this rumbling vibration noise each time I stop or idle is embarrassing (and I am sure not good for the system).

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