M103 Weird Whine: Smog Pump? - PeachParts Mercedes-Benz Forum

350SL4spd · #1 04-17-2010, 01:42 PM

Hey Guys,

My '91 300E has developed a weird whine noise when she's cold: it's a metallic whine that almost sounds more like a whistle, that only happens when you increase or decrease RPMs. The noise is based in or near the Smog Pump. If you rev the engine a little in Park while touching the Smog Pump you can actually "feel" the whistle if you get my meaning.

Can anyone educate me on the Smog Pump? How does it work/When does it work/What does it affect electronically & atmospherically (where it goes into the manifold)? There's nothing in any of my books...

Has anyone ever gutted one (if this actually is my problem)? You have to leave it in due to the damn serpentine belt...

Any info would be greatly appreciated!

Thanks!

JohnM. · #2 04-17-2010, 02:41 PM

Does it go away after the first 3 minutes or so of start-up? The smog pump is designed to pump air into the exhaust to aide in burning of excess hydrocarbons on cold startup. Nothing else. Once the engine is warmed, the EGR system does nothing and the smog pump should be free-wheeling. These pumps are notorious for failing in all sorts of crazy ways. Wide range of neat noises if the internal clutch fails, outer pulley bearings go bad, etc etc. They can also fully seize and shred the belt which is also good times.

I would advise sourcing a replacement sooner rather than later. Even if it's a used pump. Don't pay more than $100 though. Used air pumps at the Pick'n'Pull yards over here are $12.99. I bought the replacement for my car on eBay for $99, fully rebuilt. Got lucky on a bidding auction.

.

You can also remove the smog pump, block off the EGR tube, vac lines. Then get a shorter fan belt for an early car. Although I also believe the fan bearing bracket has to be changed over to the early PN, but not sure. It won't really affect your ability to pass emissions (cold startup ONLY) unless they are really knowledgeable on the visual inspection.

Good luck.

ps2cho · #3 04-17-2010, 03:36 PM

Just curious, does my 88 300TE have a smog pump? I remember the PO said it was bad, but I didn't think I even had one.

JohnM. · #4 04-17-2010, 03:43 PM

Quote:

Originally Posted by ps2cho

Just curious, does my 88 300TE have a smog pump? I remember the PO said it was bad, but I didn't think I even had one.

No. Smog pump was not introduced until the 1990 model year. You would have all sorts of extra vacuum lines, an EGR valve on the exhaust manifold, etc. It's very noticeable in the engine compartment. It sits right above the alternator.

ps2cho · #5 04-17-2010, 09:00 PM

Thanks. Is the air pump the same thing alternate name?

johnathan1 · #6 04-17-2010, 09:15 PM

My 560SEC was missing it's smog pump (PO had removed it) and had been removed very cleanly. Still wouldn't pass smog (failed visual).

Are you sure the sound isn't your belt squealing?

BJaltima · #7 04-17-2010, 09:29 PM

That's what must be making my odd (cold start-up) noise. Where is it positioned on the 4.2 liter V8?

350SL4spd · #8 04-18-2010, 11:40 AM

Thanks for all the replies.

John M:
I wouldn't say that it goes away after 3min, but it definitely goes away after about 10min. My bet is that the pump is failing internally; if the outer pulley bearings were the problem, I would suspect that it would whine all the time, not just for a second when you get on or off of the throttle.

I don't suppose there's any chance that the internals can fail & not seize the pump/shred the belt, is there?

Is there anyway to disable the electronics on the pump (ie: unplug it) and solve the problem that way??

On the bright side, I don't have to worry about passing emissions in my current location, so a delete is not out of the question. My main concern would be sourcing a belt that fit properly.

johnathan1:
Definitely not the belt. You can actually feel the smog pump vibrate as you tweak the throttle and it whines.

JohnM. · #9 04-18-2010, 02:06 PM

I will look for the exact belt part number for you. I saved all of that information when I was considering the delete a few years back. Pretty sure you just get a 86-89 300E belt wherever you buy your parts.

It's hard to say what exactly failing inside your pump. You can try unplugging the smog pump connector (near the washer/coolant bottle), and see if that changes/stops the noise earlier. If unplugging the pump does nothing, the pump is pretty much FUBAR'ed, and you should look into replacement/delete....

350SL4spd · #10 04-18-2010, 02:20 PM

Thanks John, that's pretty much the plan @ this point.

You mentioned possibly needing a different bracket to do the delete: can you dig up that part number or explain further?

Thanks!

pawoSD · #11 04-18-2010, 03:18 PM

Can't you all cheat on a smog test by installing some sort of hidden air injection blower like the smog pump in the car and porting it into the exhaust, so it massively dillutes the exhaust?

We don't have smog tests around here....MI rocks!

ps2cho · #12 04-18-2010, 03:34 PM

Quote:

Originally Posted by pawoSD

Can't you all cheat on a smog test by installing some sort of hidden air injection blower like the smog pump in the car and porting it into the exhaust, so it massively dillutes the exhaust?

We don't have smog tests around here....MI rocks!

Yes you can, but if you are polluting, you are most likely cheating yourself in the long run because your engine is not running as it should. Not to mention all the carbon footprint sharks will attack you

pawoSD · #13 04-18-2010, 04:24 PM

Quote:

Originally Posted by ps2cho

Yes you can, but if you are polluting, you are most likely cheating yourself in the long run because your engine is not running as it should. Not to mention all the carbon footprint sharks will attack you

Yes I know, but what about the folks running straight exhausts on their 560SEC's....

My car still has all emission stuff in place, including the smog pump.....I did disable the EGR valve, but that is it.

bsmuwk · #14 04-18-2010, 04:49 PM

Quote:

Originally Posted by pawoSD

Yes I know, but what about the folks running straight exhausts on their 560SEC's....

My car still has all emission stuff in place, including the smog pump.....I did disable the EGR valve, but that is it.

Good, the EGR does nothing but rob us.

350SL4spd · #15 04-25-2010, 03:19 PM

Just wanted to update this thread. I pulled the air pump today and replaced it w/ a used one from eBay ($65).

I could barely even turn the pulley by hand when I got it out.

Thanks JohnM for telling me to take care of it sooner rather than later! It was damned close to taking out the fan belt. (I thought my power steering was getting tough at slow speed...

).

I decided to pull the old pump apart to see how the damn thing works and see what the feasibility of gutting one so you could pass visual inspection, keep the original belt, and not have to worry about the damn thing.

Pics of guts:

Talk about over-engineered!

Sheesh... The impellers look like something out of Star Wars!

As far as the feasibility of gutting it: It seems possible. You'd just have to pull out the impellers w/ their bearings. I tried to get the drum out to inspect the clutch system, but the nut on the end of the shaft (mid-pulley) was frozen (I broke my 6mm allen rachet

).

But that wasn't too much of a concern on mine, as the internal bearing weren't my issue; the pulley bearings were the problem.