Conflicting Opinions on Fuel Pump Buzzing?
 

1988, 190e, 2.3L, 8v, 150K miles

I hear a rather loud "buzzing" from the fuel pump located underneath the driver side rear seat. (heard it about 4 months ago but then it went away, I think but now is back loader than before) It is definately the fuel pump that is "buzzing" because I just lifted the car and took off the plastic cover to verify that this was the source of the buzzing.

Now, I have searched this topic and read quite a few threads that this is signs of fuel pump failure. But, I have also read that the fuel pump can buzz, even loudly, and continue to operate as normal for quite some time and that the buzzing could not necesarily be a premature sign of failure.

My questions:

1) Is it safe to drive like this? I ask because this weekend I was planning on taking this car on a trip. 400 Km round trip on up and down roads/mountains. (passing trucks and buses on two lane highways is involved)

2) If buzzing is premature signal of fuel pump failure, are there any others or does it just stop functioning from one moment to the next. (car starts on first turn of key w/o pressing down on the gas - idle is very little eratic varies maybe 50 rpms if that, and at about 750-800 rpms consistent)

3) Should I change the fuel pump even though no other signs of failure? What are if any other premature signs of failure? (bought the car 7 years ago with 60K and never have changed the fuel pump)

Thanks in advance for any and all replies!!!!

My W126 has a backflow preventer valve that was causing my fuel pump to buzz. It screws into one end of the Bosch pump.

My fuel pump buzzed for several months then stopped buzzing. A few months later, I started having fuel delivery problems, most notably when accelerating. Almost immediately, I had problems starting it and soon after that, I couldn't start it at all.

When put in that context, it seems rather obvious that I had a questionable fuel pump (this car has two pumps). However, it wasn't so obvious to me at the time. I had forgotten about the fuel pump buzzing. A couple of weeks of troubleshooting here and there and I still didn't find the source, although I did discover that my EHA was leaking and that the rubber hoses in and around my fuel pump assembly were hard and cracking. So I replaced all of those and my fuel filter.

Anyway, back to the main point. It very well could continue to work for awhile. However, I would not take the car on a long trip unless I had a spare fuel pump and the tools to replace it.

Hi euronatura,

I haven't been in Guatemala, but from what I've seen on TV, I would replace a fuel pump at my convenience at home rather then doing it at the side of a mountain road. It lasted 15 years, if its the original and I would not try to squeeze another 400 kms out of it. I'd replace everything and know I'm set for another 150,000 kms, provided the rest of the car is in good shape.

Good luck

Reinhard Kreutzer

Thanks for the replies:

Q:
Did you just change the backflow preventor valve? Anyone, does this pump have one?

RKreutzer:
I have to assume that the pump that is on the car is original since I doubt that it was changed before I purchased the car with 60K miles on it. I now have 150K miles on it. I purchased the car while I lived in Miami and when transferred to Guatemala brought the car with me. So 150K miles on a fuel pump, is this good? Bad? or Average life expectancy?

Thanks

My W124 has 132K miles on it with the original pump. Still "hissing" and not "buzzing".

I will add that I have an aftermarket electric pump on my VW that buzzed even when new...moreso when starting the car and initiating fuel delivery, and then the buzz was a bit muffled...

You know what, "hissing" is a better adjective to describe the noise that the pump is making. I used the word "buzzing" in my original post because that is the adjective that I saw used in other threads posted on the subjet.

But in the end, it does more "hiss" than buzz. Is there a difference as to the operation of the pump?

I replaced mine with only 45,000 miles on it, but they were 15 years old and one was leaking. So you are way ahead of me.

Good luck with the trip

Reinhard

Thanks
 

Thanks Reinhard:

Installing new pump tomorrow morning.

Thanks again...........

Euronatura:

If it still buzzes after replacing the pump, consider what Q had to say above.

My new Bosch pumps came with new checkvalves already screwed into the pumps.

What pointed me toward the check valve was when I turned it off, I would get a little hum that would fade away in about 10 seconds. After replacement, I noticed that the pump was noticably quieter.

Check Valves
 

How do you know when to replace the fuel check valves on 420SEL?

When you start the car and it stumbles a bit, then you hear air in your fuel tank. At that point, the car runs normally. The fuel accumulator can cause the same symptoms from what I remember, but I have yet to replace that.

I'd like to hear from someone here how to drain the fuel tank properly.