'92 400E whining from air injection pump - Mercedes-Benz Forum
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#1 (permalink) Old 12-18-2013, 07:29 PM
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'92 400E whining from air injection pump

Got home today and the car has been running great. As I was pulling into the garage, I heard a whining like a bad bearing about to go. I popped the hood and tracked it to a component on the left side of the fan and above the alternator. The service manual Introduction to Service illustration labeled it #7, the pulley for the air injection pump.

A few questions:

The car has 154k miles on it. The sound just started today. How long do I have before it fails?

If it fails, am I stranded, and will it break other things?

When I search for replacement parts there are two options; the air pump pulley, and the complete air pump assembly which includes the pulley. How do I know if I need the whole thing or just the pulley.

Has anyone replaced one of these, and how tough is it? Are there any valves or things I need to replace at the same time?

I'm kinda financially tapped out (and really busy) with the holidays upon us. Oh, if this could only wait a month/1500 miles!

Thanks in advance!

Glen
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#2 (permalink) Old 12-18-2013, 07:52 PM
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I have yet to see an air pump that has a replaceable pulley.

Of course, mine doesnt have one... so I dont have to worry!
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#3 (permalink) Old 12-18-2013, 08:24 PM
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You could bypass by removing and getting shorter belt. Does the sound go away after a few minutes? If so it may not be a problem for a while.


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#4 (permalink) Old 12-18-2013, 10:02 PM
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This may help. Granted - not this site - just my first find using google.

w124 Smog Air Pump rebuild - PeachParts Mercedes ShopForum
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#5 (permalink) Old 12-19-2013, 07:13 AM
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I believe the pulley on the air pump has an electromagnetic clutch (like the A/C compressor), so it should only operate the pump during a cold startup for a short amount of time. However the pulley always spins regardless if the clutch/pump is engaged or not. If the pump is operating right, i.e. is it not engaged once the car is warmed up, yet it still makes noise... Likely it’s the bearing in the pulley. If that fails or seizes, it’ll likely take out the serpentine belt and you’ll lose all your accessories (water pump, alternator, p/s, a/c, etc…).

I would remove the belt and spin the air pump pulley by hand (should spin freely). Listen for noise and feel for any grittiness and/or play in the pulley. I would also disconnect the electrical harness to the air pump, so the clutch is not activated and see if the noise is still there after driving the car for a bit.
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#6 (permalink) Old 12-19-2013, 07:52 AM
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Clarification to my post, if the noise goes away shortly after startup it should not be an issue.
mines whined like that for years.


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#7 (permalink) Old 12-19-2013, 07:58 AM
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Originally Posted by humblejoe View Post
Clarification to my post, if the noise goes away shortly after startup it should not be an issue.
mines whined like that for years.
Correct, the air injection pump only runs on cold start for less the 90 seconds.

If this is the only time the noise is heard, unplug the pump.

The clutch is just like the A/C compressor, the pully has a bearing that spins all the time.

If the bearing is noisy, either get a shorter "bypass" belt or repair/replace the pump.

Euro non-catylitic cars don't have the pump, I'll see if I can find a size for you.


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#8 (permalink) Old 12-19-2013, 08:02 AM
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The air pump has a pulley bearing that spins any time the engine is running and a set of internal bearings that spin only when the electromagnetic clutch is engaged which is only for the first few minutes after start up (yes, you are carrying around a lot of weight that is used only about 0.01% of the time). If the whining you hear continues after the start up period (5 minutes or so), it is most likely the pulley bearing. In general, this is the most common failure on the air pump.

Bearing replacement is a fairly easy DIY. I bought a replacement bearing on Amazon Prime, had it the next day, and two hours later, all was well. I know the part number for my E320 (M104), but I don't know if it is the same as the pump used on your car. You will need to research that.

Hope this helps,

- FD

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#9 (permalink) Old 12-19-2013, 08:26 AM
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Originally Posted by Floobydust View Post
The air pump has a pulley bearing that spins any time the engine is running and a set of internal bearings that spin only when the electromagnetic clutch is engaged which is only for the first few minutes after start up (yes, you are carrying around a lot of weight that is used only about 0.01% of the time). If the whining you hear continues after the start up period (5 minutes or so), it is most likely the pulley bearing. In general, this is the most common failure on the air pump.

Bearing replacement is a fairly easy DIY. I bought a replacement bearing on Amazon Prime, had it the next day, and two hours later, all was well. I know the part number for my E320 (M104), but I don't know if it is the same as the pump used on your car. You will need to research that.

Hope this helps,

- FD

Damn, that really sounds familiar, I know I've read that somewhere before.

Anyway, part number for the bearing Flooby? Post intel like that and you need a part #

Another option is the Euro idler pully that bolts in place of the air pump.

Part number 124-330-02 42 for 1992

123 330 03 42 for 93 to 95



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Last edited by Clarkz71; 12-19-2013 at 05:20 PM.
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#10 (permalink) Old 12-19-2013, 08:43 AM
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OE bearing/clutch repair kit, if the pully is the noise only. If it's the internals, no go.

119-140-12 86 # 29 in diagram

Problem is it's $486 at parts.com. More then a reman pump.




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Last edited by Clarkz71; 12-19-2013 at 09:06 AM.
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