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  #1  
Old 03-09-2000, 01:58 AM
Nick Jamal
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Over the past two days I've taken 4 long (2hr) highway trips (~130km/h) in my 86 300E. After two of these trips, I noticed a distinct and fairly loud buzz from underneath the car when I slowed to idle and rolled down the window. Turning off the engine and then turning the key to the on position (but not starting the car) again produced this buzz. I usually hear some something powering up when doing this - always assumed it was the fuel pump but I'm not sure - and the buzz seems to coincide. Any advice?
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  #2  
Old 03-09-2000, 03:37 AM
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Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
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from what i understand, the buzzing sound is the fuel pump and is normal when pump is activated when switch is turned on. it buzzes for about 2 seconds. with engine running, pump then hizzes continuously. pls. correct me if i am wrong. thanks
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  #3  
Old 03-09-2000, 09:11 AM
Nick Jamal
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It definitely sounds like the fuel pump, at least to me, but the new buzzing is really pretty loud - unusually so - and it persists after the engine is started. I can't always reproduce it, but this has happened twice, under the circumstances described above.

[This message has been edited by Nick Jamal (edited 03-09-2000).]
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  #4  
Old 03-09-2000, 10:12 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Have it replaced soon. It will bite and leave you on the side of the road...

------------------
Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM


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  #5  
Old 03-09-2000, 10:33 PM
Nick Jamal
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Hmmm, I was afraid of that, but preventative maintenance is the best (and cheapest) kind. I've submitted a parts request, but while checking prices on other sites I noticed that the 300E is listed as having "dual pumps". What does this mean? Which one am I likely looking at replacing? Finally, any suggestions regarding new vs. rebuilt vs. used?
Thank you all,
Nick
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  #6  
Old 03-10-2000, 08:03 PM
CMCon98
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Benzmac is right; have the main pump replaced asap. Also, electric fuel pumps get noisy when they are working harder than they are designed to work. Some cars have a feed pump inside the fuel tank which feeds fuel to the main, high pressure pump. If the feed pump has stopped working, the main pump will get noisy and eventually fail. Another cause of excessive pump noise could be a blocked fuel filter, through which the pump is trying to force the fuel. Have all of this checked when you have the main pump replaced.
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  #7  
Old 03-13-2000, 12:38 PM
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Location: Pittsburgh, PA, USA
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I have had an 83' 500sl (Euro) for a couple of months now. The car runs very well but seems to have many little things that need repair, probably not a lot considering that it is 17 years old. Anyway from outside of the car the fuel pump always buzzes, I would consider this sound to be normal from my experience of electric fuel pumps. Please correct me if I am wrong. From inside though there is what I would call a steady whine. It doesn't seem to increase or decrease in pitch, regardless of driving situation or idle. The noise is louder than I would expect but, I have no experience with these older cars, I had assumed that this also was the fuel pump. Although If I had to guess I would say the sound seems to originate from the rear drivers side of the car,(opposite of where the fuel pump is). Any thoughts or experiences would be appreciated.

Marc
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  #8  
Old 03-13-2000, 03:47 PM
Andras Nagy
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Marc:

That is exactly where your fuel pump is, behind the rear right "axle". In fact, you can just drop to your knees and see it. There ought to be both a fuel pump and a fuel accumulator there; propbably put down there to keep them cool and "easily" accessible. Buy you may also be experiencing an "echo" if you think it is on the left (driver's side), for there is nothing there except your exhaust. Could it be a loose exhaust?

Anyway, it seems that German fuel pumps start buzzing when they get "old", and they will continue doing this buzzing until they give up the ghost. They do not necessarily get louder with age, just start buzzing sometime after three-four years, and someday quit. That's why most people recommend that you replace them when they start to buzz - you'll get no warning when they are about to quit.

By the way, when they get really hot, such as with warm gasoline, like when you have little in the tank and it's hot outside, they will buzz even louder, until you cool them with a tank full of cold gasoline (like what comes out of tanks buried in the ground, which is 55 degrees F. year round, below 36" of ground cover).

So the choice is yours, replace now or wait until it stops - but given Murphy's Law, that might be in a thunderstorm late one night, 100 miles from home.....Andras

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  #9  
Old 03-13-2000, 07:05 PM
CMCon98
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Another tip: The Bosch electric fuel pump in my Volvo died in traffic one day, and I jumped out of the car and whacked the pump a few times with the handle of a big screw driver. This jarred the pump to life enough to get home, where it again died. I would certainly suggest replacing a buzzing pump before it goes, but if it fails unexpectedly, try hitting it with a wrench or something, with the key on, and see if that gets it going again.
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  #10  
Old 03-13-2000, 10:33 PM
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Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
Posts: 750
so with all of the above posts, do i take it that a perfectly normal, healthy, working fuel pump must be quiet - no buzzing, hissing, no sound at all!!!
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  #11  
Old 03-14-2000, 01:36 AM
Chris Ecklund
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All pumps make noise, you just have to be really observant!!


Nick: Go see Al at Performance in St.Kitts

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Chris Ecklund
98 300 DT
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  #12  
Old 06-13-2000, 02:32 AM
Benzman500
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Mine has done that since 43,000 and now it has 215, and is still on the origanal fuel pump

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