I've been having this problem for quite a while and it's getting on my nerves lately, plus it's embarassing. When the car is started and the engine is cold, it produces a high pitch whine or whistle similar to a jet plane on the ground. The noise goes away abruptly after one minute if it's a hot day, on winters it takes a while. The noise seems to be located near the alternator, if it were the bearing I guess it would be constant. Someone told me that it could be a vacuum line with a small hole, if it's the case how do I find the proper line? Where to look in the CD manual

Thanks

Mike

Hmmmmmm, sounds like your smog (air) pump is giving you trouble. One way to check it is to disconnect the plug (it is on the pass side in front of the radiator resevoir) and see if the noise goes away. What may be happening is that when the clutch activates the smog pump, it sqeals because of a bad baering.

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Perhaps you are already aware of it, but if not, old, stiff, glazed drive belts can cause an awful lot of noise. To find out, you can spray some belt dressing or silicone spray on the belt. Even if that quietens the noise, it probably won't last long and you will need a new belt.

Good luck!

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Ted
1979 240D
160,000 miles

First, please list year of you car. My 420 makes a whistling noise in the mornings only when the weather is above 60 degrees (from about May through September). The other months it makes no noise in the morning.

When the car is hot (after running a while) or during non-summer months, it make no noise.

I was told that it was the "air filter" by my Tech. I, too, am puzzled on what exactly makes the noise. I was told that it is not harming anything and to just grin and bear it.

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'89 420 SEL
'90 300 SEL
'84 300 SD (sold it)

The car is an 88. The belts are OK and I spray them once in a while. I did not check the smog pump, but normally the pump works along with the motor so I should have the noise intermitently. In my case it happens during mornings too, I didn't pay much attention to the outside temp when it happens. Once the engine is restarted later on during the day nothing happens. The noise is very present in the alternator area, IMHO the air filter has really nothing to do with it, the housing maybe. The sound cuts off sharply as if some sort of vacuum system was cut off. I couldn't find any vacuum hoses diagram in the shop manual.

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1988 420sel
1973 porsche 914 2.0

I know what you are saying, I do not understand it myself, but 2 different Techs told me it was the air filter. Maybe I'll ask him again myself.

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'89 420 SEL
'90 300 SEL
'84 300 SD (sold it)

Alain V. you're right it is my smog pump bearing, I manually disengaged it on startup an the noise stoped, enganging it brought back the noise. Mattsuzie try doing the same thing, there is only one electrical wire that comes out of the smog pump clutch, the connector is on the suspension post in the engine bay. Thanks so much Alain!

Mihai

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1988 420sel
1973 porsche 914 2.0

Thanks , I will try that.

what is the significance of the smog pump anyway and why does it go awat during various temperature?

Thanks, will try that

also , how are you going to fix it? replace bearings? new smog pump? disconnect pump and forget about it?


thanks, glad you figured it out

I looked for the one wire in front of the antifreeze reservior and quite frankly found maybe 4 or 5 wires. How should I know which one to disengage and how do you disengage it?

Would like to try this. This has been bugging us for years.



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'89 420 SEL
'90 300 SEL
'84 300 SD (sold it)

"the connector is on the suspension post in the engine bay. "


Hate to sound ignorant, but where is that?

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'89 420 SEL
'90 300 SEL
'84 300 SD (sold it)

Mattsuzie
The easiest way, is to locate the wire on the electromagnetic clutch in front of the smog pump, then follow it right to the first electric connector. Sorry! by suspension post I meant that big bulge in the engine bay where the suspension lies underneath. The wire is between that bulge and the headlight. I may be wrong but the smog pump just pumps air in to the exhaust at startup to lower the % of CO2 and other gases that come from the rich mixture. It's a gizmo so the car will comply with emissions, if you unplug it nothing should be wrong. I'm planning to remoove it this weeken and go from there, I really hope somebody carries the bearing only, because the clutch works fine. I'll keep you posted.

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1988 420sel
1973 porsche 914 2.0

By the way, if it is the bearings, what does that weather have to do with the noise.

Also, any luck yet with fixing it?

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'89 420 SEL
'90 300 SEL
'84 300 SD (sold it)

The bearing has nothing to do with weather except for the fact that in Quebec the salt on roads they put during winter doesn't help on parts longevity. The pump is actuated on startup depending on certain engine and environnement conditions, outside air temperature can be one of these, so if the outside temperature is cold for example, the pump doesn't have to function. If the pump doesn't have to function the bearing doesn't either, so no noise. I hope I got it wright. I still have to remoove the pump, I'm having trouble with the top allen bolt, looks to be a 4 or 4.5mm head. Bottom bolts are pretty tight too. I should get tools tomorrow and by wednesday have it out. Finding the bearing should be easy if I go to a bearing speciallist.

Mihai

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1988 420sel
1973 porsche 914 2.0

I read this on this website. I think that the smog pump (air pump) cuts off due to oil temp. Anyway, any luck with this thing. Is it safe to run the car with the pump disconnected?The smog pump or AIR (air injection reaction or some such) now called secondary air on later vehicles is an after the fact emissions device.
First used in around 1970 the air was pumped into the very rich (by current standards) exhaust and partial combustion of the waste was accomplished. The first improvement was to add reaction chambers right off the exhaust port. This improved the burning (oxidation of CO to CO2 and HC's to H2o and CO2).

The process was greatly improved with the first catalytic convertor which were oxidation only. The addition of the catalyst to this firebox was a tremendous improvement except that it often oxidized N2 (over 70% of air) into NOx (various oxides of Nitrogen).

This brought about the new rules as of 1980 to regulate NOx. This brought about the lambda (closed loop) fuel system and the oxidation reduction catalytic convertor. The process used in the redux cat is the reduce (opposite of oxidize) NOx back into N2 and O2 in a first stage and use this O2 for the oxidation section. This process needed an exact amount of O2 to be effective and it actually needed a lean-rich-lean control rather than perfect stoiciometry to release the necessary O2.

The weakness in this system was the warm-up period when closed loop control couldn't be effected and where the cat wasn't hot enough to do the reduction reaction. Sooo they added your pump only for cold running (up to oil temp 130-140F (I think - switch next to oil filter housing) at which time the electric clutch (similar to A/C clutch) disengaged and no more pumping takes place. This is very important as the lambda control is ran of the O2 sensor and even small exhaust leaks ahead of it can aspirate in enough air to make the car think its lean and cause full lambda rich correction.

The secondary affect of the air injection is to rapidly heat the cat so that closed loop can start working.

The newest pumps 97 and up (I think) are all electric (no belt) and there function is monitored every drive cycle for OBDII.



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'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)