"Static" noise coming from fuel pump - PeachParts Mercedes-Benz Forum

ps2cho · #1 04-07-2009, 04:59 PM

Upon acceleration and when I let off the throttle, the fuel pump has started recently making a sort of "static" noise in the rear of my 88 300TE....

Could this be a sign of impending failure? It only started within the last 500 miles.

Thanks,

pawoSD · #2 04-07-2009, 05:34 PM

Weird.....can you hear it running in general when the car is on? I can't hear the one on our 300E inside the car, I can outside the car though....just the normal whirrr sound that most gassers have....

ps2cho · #3 04-08-2009, 01:14 AM

Quote:

Originally Posted by pawoSD

Weird.....can you hear it running in general when the car is on? I can't hear the one on our 300E inside the car, I can outside the car though....just the normal whirrr sound that most gassers have....

Yes. I can hear it inside the car and even moreso outside if I go to the rear.

Its gotta be on a quiet road and you gotta have a good ear. My dad can't hear it...but I can because I know how my car sounds. He can hear it on the outside though.

Static is the closest description I can give you. Its not a whirr...It definitely started recently...this is not something that I would have missed before.

pawoSD · #4 04-08-2009, 01:17 AM

I drove real slow on a smooth road today and still couldn't hear ours.....it might be since its a sedan there's more buffer between the sound and the interior (rear seat + trunk)....

Have you had someone rev the motor a little while you listen back by the pump outside the car to see if it makes the sound? Tried a mechanic stethoscope on it?

ps2cho · #5 04-08-2009, 01:19 AM

Quote:

Originally Posted by pawoSD

I drove real slow on a smooth road today and still couldn't hear ours.....it might be since its a sedan there's more buffer between the sound and the interior (rear seat + trunk)....

Have you had someone rev the motor a little while you listen back by the pump outside the car to see if it makes the sound? Tried a mechanic stethoscope on it?

It does the static at idle...and when it revs it gets more frequent, but about the same noise level. It is kinda intermiddent though...it's not rhythmic.

No, this is the first time I've addressed it. I thought maybe it would go away or it was something else, but it is definitely coming from the pump. Havn't noticed any difference in driving...so I figure unless it gets worse or affects driving at all I will just leave it for now.

pawoSD · #6 04-08-2009, 02:40 AM

Does the pump actually flow more fuel when giving more throttle? I've never understood if the gassers run like the diesels do....just flowing a constant volume and returning more or less of it to the tank via the return depending on the throttle usage......

I always thought that the fuel distributor takes in a steady volume of fuel and supplies what is requested to the injectors, and just sends the rest back to the tank via the return line....

Is that how it works?

ds190 · #7 04-08-2009, 11:06 AM

I've got the same issue with my 91 300TE, and have since I bought it 50K miles and six years ago. It is steady, and gets louder when the tank is more than half empty.

The 91 has two pumps; I don't know about yours. The rear most pump is the noisy one, and I bought a replacement for it, which sits in the spare tire wheel well ready to be installed

Somebody somewhere suggested removing the noisy pump, wiring it in reverse, and back flushing it to remove possible grit in it. I was going to try that too, but never did.

So yes, a noisy pump will fail, but when is tough to call. The factory says replace it now, because the failing pump increases the "load" on the other pump, potentially causing it to fail before it's time. Actually, the factory says replace both together, even if only one is noisy, IIRC.

E150GT · #8 04-08-2009, 11:12 AM

I think I have the same thing on my 420sel. Sometimes when I start it, it will make a noise coming from behind the rear seats(fuel tank?). That has happened every once in a while for three years now. Not sure what it is. If I go outside, I cant hear the same noise, but I can hear the fuel pumps.

pawoSD · #9 04-08-2009, 12:42 PM

Maybe my fuel pump is just in excellent condition.

It does have a new filter about 4,000 miles ago.....

ps2cho · #10 04-08-2009, 01:50 PM

Does my wagon have 2 pumps in the 88 model?

E150GT · #11 04-08-2009, 01:52 PM

Quote:

Originally Posted by ps2cho

Does my wagon have 2 pumps in the 88 model?

probably if it has continuous injection.

ps2cho · #12 04-08-2009, 02:00 PM

Quote:

Originally Posted by E150GT

probably if it has continuous injection.

Where is the other one located? I only know of the one that sits next to the accumulator.

E150GT · #13 04-08-2009, 03:33 PM

Well maybe it only has one. Mine are side by side.

pawoSD · #14 04-08-2009, 04:10 PM

Quote:

Originally Posted by ps2cho

Where is the other one located? I only know of the one that sits next to the accumulator.

I think most of the M103 vehicles only have 1, there was an update in the MB EPCnet that says at some point they went to 1 pump, probably early on. Mine only has 1 as well.

ds190 · #15 04-08-2009, 06:07 PM

The 124.090 wagons with engine 103.983 have two fuel pumps in a series. The second is suspended on rubber rings between the rear axle and fuel tank, and has a black plastic cover over it about the size of it.

The second pump is supposed to "prevent the formation of vapor bubbles", and the FSM has instructions on retrofitting one pump cars to two! Apparently the one pump 103.983 sedan models were 1988 and earlier.