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Old 01-20-2006, 12:23 AM
86560SEL's Avatar
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Join Date: Jan 2003
Location: east Tennessee (southeast USA)
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How important is the "A.I.R." pump or "SMOG" pump?

I am wondering just how vital are these pumps to the drive ability to Mercedes? I have saw cars in the past where these things have been disconnected or completely removed, especially on the older cars, but still running fine.

The one on my MB has had the hose removed and the belt removed from it, so there is no pump operation, but my car still runs fine. I am wondering- would it run even better if a new one were in place and hooked up? Could this be part of my engine stalling when warm problem? I looked at my pump and it appears to be seized up. It will not turn. There is also something running out of it.

I know a new one is very costly - about $900, but I know where some good used ones are for a much better rate. Should I have one installed, or is my car not affected by this item not operating? It does not seem to affect the older cars, but I know these Mercedes are a horse of a different color and wondering if it is indeed an issue on these cars. I know that it basically sends "unburned" fuel back into the engine - or something like that?

They started putting these on some cars back in the mid to late 1960s (American cars) - especially the California models, then on more cars in the early 70s. My old 72' Buick Electra had one and luckily, it was still in perfect order.

Thanks again.

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Old 01-20-2006, 03:21 AM
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Location: Wimberley, TX
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I may be wrong but as I understand it, it really only comes into play during cold starts in the first few minutes of operation.

In any case, mine's been disconnected since I bought it. Austin just recently added a smog inspection and my MB indy said I'd need it if I had my car inspected in Austin. However, I live in Wimberley, a small town in the area and there are no such requirements here. The car just passed inspection this morning.

1988 MB 560 SEL 138k - Desert Taupe w/ Cream Beige Interior.

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Old 01-20-2006, 04:40 AM
420 SE's Avatar
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Join Date: Sep 2005
Location: Coolum Beach, QLD, AUS
Posts: 284
Well many of those of us outside the US don't have them at all!

Our cars run fine without them. I've read a fair few threads where others have disconnected them without any problems, but I imagine if they (MB) had to put that rubbish on for the US market - there's probably some other junk on your cars as well that was put on in the name of emission control.
1988 W126 420 SE

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Old 01-20-2006, 08:10 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
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The system even today is purly EMISSION related. Helps to warm the catalyst more quickly to allow the emissions durning warm-up to be lower & allow the catalyst & O2 sensor to work sooner!
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Old 01-20-2006, 09:18 AM
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Join Date: Aug 1999
Location: Florida / N.H.
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Originally Posted by M.B.DOC
The system even today is purly EMISSION related. Helps to warm the catalyst more quickly to allow the emissions durning warm-up to be lower & allow the catalyst & O2 sensor to work sooner!
.To add to MB post....the shift delay is also another system that they put in there for the same rapid warm-up aid....many guys disconnect the pump and plug the delay line, knowing that if one just revs the engine a little before taking off and using a lower gear selection until the car is a little warm accomplishes the same ... the idea is to get the ECU into closed loop asap..that's about it.
The Euro cars that do not have the punp also do not have a cat. to my knowledge.
The problem w/disconnect is CE activation.
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Old 01-20-2006, 10:22 AM
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Join Date: Jul 2004
Location: New Orleans, LA
Posts: 340
W126 had it

On my '86 420SEL, the pump began to whine when the engine was started cold -- of course the pump only operates then. Never having heard the dreaded timing-chain rattle, I thought the noise might be that.

My mechanic disconnected the plug which powers the pump and said, "You're good to go." I ran the car for nearly 4 years after that with no problems.

(Though I didn't need to worry about emissions testing in Lousy-ana.)
* *
-- Paul W. (The Benzadmiral)
('03 Buick Park Avenue, charcoal/cream)
'97 C230, smoke silver/parchment; '86 420SEL, anthracite/light grey; '84 280CE (W123), dark blue/palomino
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Old 01-20-2006, 10:29 AM
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Join Date: Apr 2005
Location: Northern Louisiana
Posts: 481
I agree; Junk

My '86 420 also operates the pump only on a cold start, it's getting noisy, so I am unplugging it. Also in Lousey-ana (northern).
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Old 01-20-2006, 06:41 PM
'90 300se, '95 c280
Join Date: Oct 2005
Location: Honolulu, Hawaii
Posts: 112
I once disconnected the electrical connector and plugged the vacuum line on my california spec car for offorad testing purposes, but found that I would immediately get the CEL then the system engaged the pump the second time around after starting up. I don't remember the error code, but I recall that reading from the O2 sensor is checked, and won't check out if the pump is removed/disabled. Or is there a trick for that as well?

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