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  #1  
Old 11-12-2001, 10:09 AM
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disabling airpump

from another thread i discovered that my airpump is probably on its last legs. i hear it whirring for a minute or so in the mornings and thought that the noise what probably within limits.
what's the downside to just disconnecting it? it seems like an expensive repair if it's only job is to help the cat converter while it's cold. i'm assuming it's some epa cold start requirement that is being addressed...
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  #2  
Old 11-12-2001, 10:29 AM
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I repaced the smog pump on my daughter's '88 420SEL; I understand that not only is it possible to cause failure of an emissions test, but also that not repairing it may lead to a premature (and expensive) catalytic convertor replacement. See:

1988 560 SEL Air Pump Seized

http://www.peachparts.com/shopfor...?threadid=16303

http://www.mbca.org/discussion/thre...rch=smog%20pump
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  #3  
Old 11-12-2001, 10:44 AM
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My pump appears to be okay on my 300E (from the outside), but what noises should I be listening for that would indicate problems?
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  #4  
Old 11-12-2001, 10:46 AM
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We had a noticeable screech when starting up, which lasted several seconds. As mentioned in the other threads, the pump and the connecting valves should be checked.
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Old 11-12-2001, 11:10 AM
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mine doesn't screech just yet but makes a purring sound that sounds like an impeller that has bad bearings or is making contact with its housing. the sound that mine makes starts subsiding almost immediately but i understand that the fact that you can hear it makes it suspect.


found the definitive thread on this:

air pump---do without???
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1993 300e-2.8
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Last edited by jsmith; 11-12-2001 at 12:34 PM.
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  #6  
Old 11-12-2001, 02:06 PM
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If you do disconnect the AIR pump, a couple of things to know.

There is a switch-over valve that should also be disconnected. This valve is wired in parallel with the feed wiring to the pump clutch. So, when the pump is energized, so is the sw/over valve.
[ the purpose of the s.o.v. is to allow opening vacuum to the air check valve between the pump and the exhaust . Otherwise, the pump
can not pass the air to the exhaust]
If this is not done , this check valve is opened when the ECU calls for AIR. [ no good]
But if you disconnect it electrically, you will bring up a sov code.
So a BB in the vac line between the sov and pump check valve solves that one. [ leaving the sov plugged in to fool the diagnostics module].
But , unplugging the AIR clutch magnet to disable the pump also throws a code.
Takes a while to pop, but it will. On your car with the led/sw combo, this is easy to erase when needed. But i think [ have not tried this yet], a small lamp for circuit completion at disconnected pump feed will do that one.
If the noise is only coming from a pump when energized, disconnecting will work, but if a pump is noisy even in the off mode, it has bad pully bearings and has to be replaced.
As far as cat damage and EPA, I really don't think the 20/30 seconds that this pump is called for makes a big difference. These cars with Heater style 02 sensors go into closed loop
quickly, and the pump is never called for in closed loop.
My own opionion is cat damage is more probable with egr disconnect than AIR. [ On you model, anyway]
I also think that a lot of pump failures may be that the sov/ck. valve are at fault and possibly damaged the pumps by not closing down when needed [ ie. - closed loop]
Not advocating disconnecting anything, just pointing out some of the particulars of the systems operation, as I know it.
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  #7  
Old 11-12-2001, 04:49 PM
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Arthur,
Are you a member of the Granite State Section of the MBCA?

John
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Old 11-12-2001, 05:07 PM
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John.

No, I am not, but we do have a loosely knit friendship type of club of Benz-Heads
here in the Southern part of the Granite State.
[ Quite a Bunch, if I do say so...]
Anyway, there is no membership or anything like that, just a few guys who coop the shop [ my Barn] and all own some Benzs. Mostly hobbiest with Vintage stuff, but we also daily-driver later models and share knowledge/tools, etc.

Are you from NH.?
Arthur
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  #9  
Old 11-12-2001, 05:27 PM
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Hi Arthur,
No I`m from Mass on the Conn\RI border. I belong to the Minuteman Section. Either Granite State or our Section do the Faber Rallye every year. This year it was in southern Maine\ NH.
You should think about joining the Mercedes Club, you don`t have to be active the best part might be the bimonthly mag. Very well done tech, History new stuff on and on. Oh every year they raffle about 5 cars, open to members only!!!!
If you think about joining the # is 1-800-637-2360,use my member# P006621, we get points.
I`m not the member chairman or anything, but the mag is just great. Old cars restorations,new cars, everything.
By the way have you ever been to BayBerry Classics, near Portsmuth, and RT 95, fantastic!!!!! It was part of the rallye, its a time warp,cars of every make and year.



John
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