Air pump question (smog pump) '90 300SE
 

So I replaced the broken hoses going to the air pump, and re-connected the wire to the pulley clutch. The previous owner had disconnected it, I had assumed because the hose was shot anyway.

The thing sounds like bolts in a blender when the clutch engages.

1) How important is the air pump?
2) Is it worth replacing?
3) Will the pulley bearings hold up even though the inside sounds like hell? It sounds fine when it's unplugged.


I guess what I am really asking is do I need to replace it? Will my Caty clog up without it? I'll bet they're ungodly expensive.


Thanks!


-tp

Just went thru this with my wife's E320 wagon with a M104 engine.

Idler pulley bearing failed, locking up the sheave, making the car undrivable.

After buying the rebuilt air pump, and check valves that need to purchased to accommodate the warranty, and a new belt, I was out $661.00.

Might get a bit back for the core, but the banged up idler puller will kill most of the core charge.

Jim

OUCH!

That's what I was afraid of!!

I think I'll just unplug it and hope the pulley bearing holds up. It sounds okay until the clutch kicks in.

I just hope that doesn't have long term consequences for the catalytic converter.


LAME!!!

What exactly does this pump do, and why is it needed?

That's really interesting because my 1989 300SE doesn't have an air pump but my 89 420SEL does. Your 1990 300Se has the CIS-E ECU and controlling the air pump but my 420SEL has it operating when the ECU is not funcioning, when the OVP fuse is blown. Here are the conditions, all apply:

1. Coolant temp is above 62 F
2. engine speed is below 2500 (how this is determined I don't know)
3. Throttle full load contact is not engaged (???)
4. CIS-E control unit is not operating.

see the schematics page 110/16 and 110/17 (PDF pages 40 and 41)

To answer the previous question, the air pump injects air into the exhaust port to promote complete combustion under certain conditions, like when the engine is just started.

Lovely.....I hope the air pump on our new 300E lasts a while! :eek: It seems to be running smoothly currently...... :o Why o why do gassers have to be so complicated.....

I simply removed it on my '90. Went to the '86-89 M103 brackets, it all bolts up. You just need the '86-89 fan bearing bracket and of course the alt bracket itself. I did the extra to just tidy up the engine bay.

You could always just remove the air pump and short belt it. :)

I believe it is an attempt to help with excessive cold start emissions (quicker converter light off, my F150 had this along with most Small Fords of the era), don't forget MB also added EGR on the '90+ cars...

Awesome to know that! I know what I'll be doing now if her car's air pump bites the dust. :D :D

Yes, that is excellent to know. I might just do that to clean up things and make some room in there.

One more thing to scout for at pick 'n pull.

Don't forget to check the dipstick o-rings, those are vac leaks too...

So you can remove the air pump and just put in a shorter belt? Leaving everything else the same? Or do you need to swap other stuff too?

Does anyone know? I'd like to get the appropriate stuff ordered so I can get to work on fixin' up the 300E....

Well, I haven't tried the short-belt approach.
I just unplugged the pump about 10 years ago - and also plugged the vacuum line to the valve. That way, the valve will stay closed all the time. There is a 1-way check valve in the air line also, but why not help it out. Ig the 1-way failed, exhaust gas would reverse-flow up into the pump.

Also, the idler bearing in the pump is replaceable for not too much money, and easy to do. So, leaving the belt on the pump, just turning the idler bearing is a good option.

DG

Our air pump still seems to work smoothly, so I think I might just replace the belt and idler pulley for now (and inspect everything else for play) and see how it goes....if the pump gets noisy I will unplug it.....