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Secondary air pump question

Discussion in 'Electronics' started by 650max, Jul 9, 2010.

  1. 650max

    650max New Member

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    Hi guys

    I've recently replaced the dodgy air pump on my C32 with a replacement off ebay (yes I fitted a new relay as well)

    I decided to play with the old one to see what was wrong so took the filter end cap off, lo and behold the impellor spins freely so I connected a 12v power supply to the terminals (used a battery charger), it spins momentarily before the overload in the charger trips with the ammeter off scale (above 5 amps), question is, what current would the pump normally draw in service? I can't find which fuse protects it, is there a chance it's just been a burnt out relay in the 1st place?

    cheers

    Max
     
  2. markjay

    markjay Hardcore MB Enthusiast

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    Sorry, not too familiar with the particular setup on Mercs, but.... generally speaking secondary air pupms are meant to reduce emissions while the engine is cold and has not yet reached its normal working temperature.

    These pumps can become noisy with time and many owners chose to simply disconnect them - MOTs are carries-out at normal engine running temperature anyway so the emissions test will not be affected by the disconnection of the secondary air pump.

    Not sure if this info helps though....
     
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  3. Swozza

    Swozza Hardcore MB Enthusiast

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    In my case it was the relay that burn the pump out. How do I know this, because the mistake of not replacing the relay was made. I'd say the pump burnt out after 100 miles.
     
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  4. Alps

    Alps Hardcore MB Enthusiast

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    disconnection would cause the engine management light to come on!

    mine had a burnt out relay, was replaced and all is still fine 8 mnths later
     
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  5. OP
    OP
    650max

    650max New Member

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  6. jaymanek

    jaymanek Authorised Forum Sponsor Authorised Forum Sponsor

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    Yes its normally the relay that causes the pump to fail.. Did you change the relay? I dont think there is a fuse, just the relay.
     
  7. misfire84

    misfire84 Hardcore MB Enthusiast

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    the engine managment light doesl not come on as I have had the air pump disconected for 4 months now and no engine check light on , the Relay is still conected the valves blanked off . next job is to put a blanking plate on the head so the vacume valves can be removed totaly so tidy up it up .
     
  8. OP
    OP
    650max

    650max New Member

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    I thought I'd investigate things further as I've now got 2 pumps, neither of which is working right? .... Wrong!

    Put a motorbike battery across the pump terminals and both run fine, connect an ammeter in and they both show as drawing 0.5 amps, not excessive at all.

    With the engine cold and the pump removed, start engine and I have 14.4 volts across the pump wires and the solenoids/vacuum valves are obviously open because of a little blowback through the hose, very quickly connect the wires to the pump terminals and..... nothing and about 15~20 seconds later, the tickover drops and the vacuum valves close so obviously the ECU has decided it doesn't need the pump any more, at this point the voltage across the pump wires drops to about 8 volts.

    So now I'm confused, with a 12 volt battery connected directly, the pump runs fine but won't run at all with 14.4 volts supplied by the pump wiring, can this be down to the relay? Any suggestions?

    cheers

    Max


    P.S.

    If your pump is noisy, this will probably be down to the bearings in the motor, they can be replaced if you're careful, size is 608RS, I've just got a pack of 10 off ebay for £3.50 inc postage, C2 grade.
     
  9. OP
    OP
    650max

    650max New Member

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    Quick edit

    Tried a different, brand new relay, the voltage at the wires is now 12.5 which drops to as near zero as makes no difference once the cold start system shuts down, still can't get the pump to run so my only idea is the startup current for the pump motor must be too high?
     
  10. Justin1600

    Justin1600 Hardcore MB Enthusiast

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    The most common problem with this system after the relay going wrong, is the air pump switch over valve. Change this and then re-try it mate, they are only about 19 quid
     
  11. OP
    OP
    650max

    650max New Member

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    Cheers Justin

    Can you tell me whereabouts this valve lives or what it looks like?

    Max
     
  12. Justin1600

    Justin1600 Hardcore MB Enthusiast

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    It is probably at the front of the egine, it will have two vacuum pipes going to the top of it and a multiplug. Black in colour
     
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