92 300E air pump - PeachParts Mercedes-Benz Forum

RDMosley · #1 03-29-2003, 02:38 AM

I just purchased a 92 300E with 127k miles on it. There is a moderate grinding noise under the hood. One shop says it is Alternator bearings, another shop says it is air pump bearing. I have listened and tend to think it is the air pump.

After reading some of the threads here I have several questions.

1) What is the best source for a used or rebuilt air pump?

2) Is replacing the air pump a do it yourself job?

3) I have read that the air pump is not really necessary for the performance on the car and can be disabled. Can anyone send me instructions on how to disable it?

Thanks so mucg for the help

Richard

joe p · #2 03-29-2003, 09:52 AM

OK, common noise locations in the belt drive for a 103 engine.

Fan idler bearing bracket.
Secondary idler pully (mounted to the fan bracket.)
Air pump clutch idler bearing (test this by activated the pump clutch by way of jumping power and ground to it while at idle)
Tensioner idler
On occasion the front bearing in the alternator will give it up as well.
waterpump

Get a stehiscope (nope, cant spell) and check it. Just dont drop the thing into the drive, your ears will ring for a month.

Joe

JDUB · #3 03-30-2003, 11:57 PM

The bearing was squealing on the air pump of my 103 Motor and I removed it and put on a shorter belt. The car has been fine without it.
The pump is veary east to remove and replace if that is what you want to do. I removed mine in about 15 minutes. The most time consuming part is replacing the serpantine belt on a 103 engine.
The air pumponly functions for a short time when the engine is cold anyway.
To examine what is making the noise get a metal bar like a long 1/2 inch drive extension or pipe and hold it to your ear and place it on the air pump , alternator etc. to see where the noise is coming from. Be extremely careful.

pmizell · #4 03-31-2003, 12:16 AM

To disable the AIR pump, simply disconnect its 2 pole electrical connection .... follow wire from pump to fender wall next to wiper resevoir and you should see it.

Arthur Dalton · #5 03-31-2003, 07:36 AM

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You also have to block the vac line from the AIR swith-over-valve to the AIR control valve. The SOV is wired in parallel with the pump connector and will still open with the pump unplugged..
A BB in the line works here....

RDMosley · #6 04-01-2003, 06:52 PM

Thanks for all the good info. I finally wound up just replacing the pully and bearings on the pump. JDUB, I would be very interested in knowing what length serpentine belt is required if I ever decide to remove the air pump entirely.

Rich

400E · #7 04-01-2003, 08:50 PM

Do a search. I recently posted 2 web sites which supply rebuilt MB air pumps and offer excellent warranties.

G-Benz · #8 04-02-2003, 09:53 AM

Quote:

Originally posted by RDMosley
Thanks for all the good info. I finally wound up just replacing the pully and bearings on the pump. JDUB, I would be very interested in knowing what length serpentine belt is required if I ever decide to remove the air pump entirely.
Rich

As far as serpentine belt size, pick the length for your vehicle that would be correct for the same configuration "sans" one ancillary unit...like the A/C. I believe they are sold that way.

Curious as to how you managed to procure the correct bearings for that pump?

One of the big issues with why we have to go to rebuilt units is that the bearings are a metric-size, impossible-to-find component...otherwise, most of us would have just cracked open the air pump housing and done the swap ourselves!

Share us your secret...

BTW, the sole purpose of the air pump is to spool up the optimum emission efficiency more rapidly. This is most important in Europe, where laws require emissions tests to be performed within 60 seconds of starting the engine.

Here in the US, it's not that critical, so the pump could be deleted from the system entirely.

RDMosley · #9 04-02-2003, 10:11 AM

Well I had located a rebuilt pump and was all set to order it and install it myself. I decided to take it by my local benz mechanic and just ask if there were alternatives such as removing the pump altogether. He did not recommend removing the pump but said he could replace the pully and bearings. I asked him specifically and he said MB does sell this separately. Apparently it is quite a BEAR to remove from the pump assembly though. So I got the new bearings and pully for about one-third the cost of a rebuilt pump.

Rich

G-Benz · #10 04-02-2003, 10:18 AM

Cool! I'll have to ask around...I'm starting to hear noises on mine...

pmizell · #11 04-09-2003, 05:22 PM

Arthur D wrote:

Quote:

You also have to block the vac line from the AIR swith-over-valve to the AIR control valve. The SOV is wired in parallel with the pump connector and will still open with the pump unplugged..
A BB in the line works here....

Arthur, are you saying the AIR clutch still engages with the vac line still connected? Could you explain please what blocking the SOV vac line accomplishes? Thanks

Arthur Dalton · #12 04-09-2003, 06:04 PM

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No. If you unplug the clutch connection, naturally, the clutch will no longer energize to turn the pump..
But the ECU also sends this very same electrical signal to the Air control valve SOV . [ parallel circuit].
This SOV , when energized, allows engine vac flow to actuate the AIR Flow Control valve between the
the pump output and the engine..
So, if you do not BB the vac
line , this valve will still open [ even though the pump is off]when the ECU calls for AIR system activation. {One could also unplug the SOV electrically. but once this is done , the inactivity of the SOV will have a tendency to gum up in the closed position]

The BB in the line works well and can be changed back to stock by simple removal and re-plugging of AIR pump connector....