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#1
12-07-2008, 05:39 PM
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91 300SE Secondary Fuel Pump
I was noticing a buzzing sound coming from the rear and thought the fuel filter must be clogged and the main pump working overtime to compensate. When I went under to replace the filter I noticed the secondary fuel pump and thought it might be the source of the sound instead, and indeed after starting up the car, a distinct high piched buzz could be heard coming from the secondary pump.
I gripped the pump tightly to make sure it wasn't just a vibration but the buzz persited from inside the pump itself. Does this sound indicative of a malfunctioning pump or could it be working overtime due to a bad fuel filter as I had suspected of the main pump? Is there any other concerns I should have regarding the sound this pump is making, and how much of a risk is being taken driving the vehicle while this condition persists? 
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#3
12-08-2008, 08:17 AM
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That car has only 1 pump & that is making the noise. Gravity feed system.
__________________
MERCEDES Benz Master Guild Technician (6 TIMES) ASE Master Technician Mercedes Benz Star Technician (2 times) 44 years foreign automotive repair 27 Years M.B. Shop foreman (dealer) MB technical information Specialist (15 years) 190E 2.3 16V ITS SCCA race car (sold) 1986 190E 2.3 16V 2.5 (sold) Retired Moderator
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#6
12-08-2008, 10:04 AM
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When I bought my MB in 1997, the fuel pump whined. It continued to do so and lasted for 9 more years.
The new one I installed in 2006 also whines occasionally. I'm not saying to ignore it, just saying you may have a noisy fuel pump even after installing a brand new one. I stuck with the Peirburg brand as that's what the car came with. Wiring/connections set to work with that pump.
__________________
Mike Murrell 1991 300-SEL - Model 126 M103 - SOHC "Fräulein"
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#7
12-08-2008, 02:00 PM
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Mine is audible....perhaps you could call it a whine....but it seems to work fine....I've heard lots of whiny gasser fuel pumps....seems to be fairly common.
__________________
-diesel is not just a fuel, its a way of life-  '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k)
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#8
12-09-2008, 03:01 AM
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Yup, no dual pumps on the I6 in the W126.
Just replace it. It should be audible but not noisy.
__________________
I'm not a doctor, but I'll have a look.  '85 300SD 245k '87 300SDL 251k '90 300SEL 326k Six others from BMW, GM, and Ford. Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]
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#9
06-17-2009, 06:24 PM
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Well, the pump finally failed.
Failed a couple of weeks ago, and I've just been driving Lead Angel (my silver 300SD beater), until she took a nosedive after loosing a couple of belts... Anyhow, I'm looking for a good fuel pump replacement guide. I've searched around a bit but haven't found anything as good as the belt replacement guide for the 300SD. I decided earlier to start taking parts off, and I pulled off the main hose going into the pump...I don't know why I thought the fuel would stop. Heh. Some other car I've worked on stopped leaking fuel once the pressure had let off... I guess since this is a gravity feed it's not the same. So, what do I have to do? Plug up the main hose after disconnection while I do the rest of the install?
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