Fuel pump noise: what does it mean?

[gathermewool]

97 Subaru Legacy (AWD) with 203k miles.

I've been lazily trouble shooting a fuel pump noise for a while now with very little results. It all started out as a rattle that sounded very similar to a loose heat shield. I'll skip through all of the things that it wasn't, since the below seems to rule out most things. Enjoy : )

In a well ventilated shop, I slowly lifted the pump assembly with the motor running (and the fuel pump plugged in.) The vibration/rattling was still present, so the thought that the fuel pump bracket might be vibrating against the inside of the tank can be ruled out.

With the pump assembly detached from any structure - held in my hands alone - I assume the issue is with the pump itself. I completely removed the whole pump assembly and, after cleaning away all of the flammable fuel from the pump and letting it sit to dry, I very quickly bench tested the pump by applying 12V directly to the contacts for a brief moment. The pump whirred to live and sounded completly normal; however, the pump was only energized for a VERY brief time, so it may not have spun up to full speed. I wasn't gutsy enough to run the pump dry for any extended period - I was hoping for something gross and obvious right away.

Btw, I've had an in-drive idle vibration - not necessarily rough-running, per se' - since changing out both CV shafts. I replaced one of the shafts again; no change. The fuel filter is also new; no change. I'd really rather not have to change out the other other CV shaft, but I may just to rule it out. I know vibration while not moving from a CV shaft seems odd, but it has been explained as the cause of vibration by some Subie owners. May not be relevant, but I figured I'd throw it in there.

Any ideas??? I supposed I should buy a gauge and simply test the system pressure, but I wanted to know what you all thought abuot fuel pump sounds, and if any foreshadowed a not-so-distant death.

 

[JHZR2]

I do not think the noise is an issue, as it has so much to do with placement, and the sound varies from vehicle to vehicle, Ive found. That said, it is critical that you get flow and pressure up to spec.

Ive read that fuel pumps will use more and more current to do their job as they age/degrade, so you might see what kind of amperage it is pulling versus what it is rated for. That will take a lot of digging though...

Ive found that with the right fuel adds (FP60 and MMO have done this in my experience), the noise can be decreased, though it will always be there.

I would imagine that bad bearings could cause funny sounds and intermittent vibration...

 

[Jim 5]

I had a fairly noisy fuel pump on my '98 Chev K1500 that I bought used. It was noisy for about 5 or 6 months and then it failed.

Hopefully you're not going down that road.

 

[chrome]

I had a fuel pump starting to make an audible hum a while back... I ignored it. One evening, after parking for a few hours, the car would crank over but won't start. After a few minutes of cranking, it fired up.

The next time a few days later, the pump died permanently.

A noisy fuel pump is typically a precursor to an imminent failure. If you don't want to risk being stranded away from home during a blizzard, I would suggest replacing it.

 

[gathermewool]

I should have mentioned before that it has been making this noise for a year + now. The only verifiable difference between when the noise first appeared and now is the length of time to start the car. A year ago, the car would immediately fire to life. Now, it seems to take a full second to second and a half to fire up. Doesn't seem bad, but different.

I absolutely hate throwing parts at a problem, but, to me, hearing and feeling the pump is definitely raising some red flags. The flags are small, though, since the car does start every time, and rarely does it bog or hesitate. Better safe than sorry, though, right? Can you guys recommend a good fuel pump to me? I don't mind paying for quality. I plan to run this car into the ground, then buy the same model with lower miles, and transplant all the goodies I've updated or fixed when the time comes, so paying for quality isn't a big deal. Darn it am I going to be upset if the the issue remains after the C/O...

JHZR2, thanks for the suggestion about the current. While I hate throwing parts at a problem I don't mind buying new toys, and and a current meter would be a nice addition to the pile of gadgets I've got laying around. haha.

 

[gathermewool]

I found a Bosch pump with a lmt lifetime warranty for just over $100, which qualifies me for the $50 online coupon...hmmm

 

[Jim 5]

That sounds like a good deal. If you can supply the labor yourself, $50 net pricing is about as cheap as one can imagine to replace a fuel pump. As someone else said, better to do it when time and venue is convenient. The alternative is being stranded somewhere in the winter.

 

[gathermewool]

You guys are right. I'm going to order the pump before the AAP deal ends. One more question, though: Should I replace the pump screen? When I pulled the pump, the screen looked perfect - no gunk, debris or anything. Part of the ltd lifetime warranty for the pump says a new fuel filter and pump screen must be purchased. I'll give Bosch a call tomorrow, since I just installed a new filter last week, and would rather not have to buy a screen.

I appreciate all of the advice, guys.

 

[Jimmy9190]

I just replaced the fuel pump on my truck with an AirTex pump from AAP and it came complete with the fuel filter and sock if there is a screen it must be internal. Just a suggestion, but maybe there is an Airtex pump for your car that is complete like that with all the parts you need in one unit.

 

[Big_Ed]

On some vehicles, if the pump stops running (if it's the type inside the fuel tank) You might be able to get it running again (possibly long enough to get home or to a repair shop) by smacking the underside of the fuel tank with a rubber mallet several times.

And I agree, that a noisy pump could very well be on it's way out. Also listen to the pump as it pressurizes the fuel system right before you start the engine. I had a fuel pump go out on my 97 GMC K1500 a couple years ago, and the giveaway was it sounded like it wasn't running as fast for the first few seconds. The bummer of the whole deal was that a month later the truck was totalled in a flood. Over $600 down the drain! Too bad the pump didn't last one more month.

 

[willix]

I would be suspect of any noisy pump. There are always at least a dozen Chev's & GMC's PU's in the fleet I work on. 96' & up would fail frequent, but warned you with the buzzing.

 

[nthach]

I'd stick with a Denso pump, but more than likely the Bosch will be a Japanese-made one.

Our van gave us the whine of death before the fuel pump died weeks later. I used a Bosch turbine pump, which sounds quieter than the OEM Walbro.

 

[demarpaint]

Originally Posted By: Big_Ed
On some vehicles, if the pump stops running (if it's the type inside the fuel tank) You might be able to get it running again (possibly long enough to get home or to a repair shop) by smacking the underside of the fuel tank with a rubber mallet several times.

And I agree, that a noisy pump could very well be on it's way out. Also listen to the pump as it pressurizes the fuel system right before you start the engine. I had a fuel pump go out on my 97 GMC K1500 a couple years ago, and the giveaway was it sounded like it wasn't running as fast for the first few seconds. The bummer of the whole deal was that a month later the truck was totalled in a flood. Over $600 down the drain! Too bad the pump didn't last one more month.


I got my Caprice home once by banging on the gas tank, actually I was kicking it. It worked, got me home, and I replaced the fuel pump.

 

[gathermewool]

You guys have talked me into it - I'm going to buy a new pump. I've been pretty lucky so far in that she has 203k, but still starts every time for me. The last thing I need is to be stuck on the side of the road fiddling with a dying fuel pump. I'm sure the hypothetical failure would occur while I had a full tank of gas, too! haha

Originally Posted By: nthach
I'd stick with a Denso pump, but more than likely the Bosch will be a Japanese-made one.

Our van gave us the whine of death before the fuel pump died weeks later. I used a Bosch turbine pump, which sounds quieter than the OEM Walbro.


I think I've heard more about Denso in the Subaru community than Bosch, but Bosch is a name I recognize for quality. More based on hearsay than any experience with Bosch, but isn't that how most of us make our infrequent purchases on these types of components?

The Denso kit is $90 more than the Bosch pump by itself. The Denso pump also only has a 1 yr warranty while the Bosch has a ltd lifetime. There is no Denso pump-only option, just the kit. What's in a kit, btw? Is it just just the sock - the thing I was calling a screen earlier (sorry about that.) - or is there more to it?

Originally Posted By: demarpaint
Originally Posted By: Big_Ed
On some vehicles, if the pump stops running (if it's the type inside the fuel tank) You might be able to get it running again (possibly long enough to get home or to a repair shop) by smacking the underside of the fuel tank with a rubber mallet several times.

And I agree, that a noisy pump could very well be on it's way out. Also listen to the pump as it pressurizes the fuel system right before you start the engine. I had a fuel pump go out on my 97 GMC K1500 a couple years ago, and the giveaway was it sounded like it wasn't running as fast for the first few seconds. The bummer of the whole deal was that a month later the truck was totalled in a flood. Over $600 down the drain! Too bad the pump didn't last one more month.


I got my Caprice home once by banging on the gas tank, actually I was kicking it. It worked, got me home, and I replaced the fuel pump.


I had to do the same thing with a dying starter motor on a 92 Toyota Paseo back in HS. Click-click-click...curse-curse-curse...bang-bang-bang...click-vroom!

 

[nthach]

The Denso kit includes the pump to hanger connector kit and the strainer sock. The Bosch pump - or the one I installed didn't have a strainer sock but a Airtex one fit perfectly.

Looking at the Rock Auto stock pics, one pump appears to be made in the US, the other one appears to be made by Denso or Hitachi.

 

[gathermewool]

So, $90 for the two clamps, strainer, 2" fuel line, pump clamp and pump koozy? Seems convenient, but how much is the kit really worth - maybe $40 on the HIGH side? Is the denso pump $50 better than the Bosch, especially considering the Bosch comes with a ltd lifetime warranty?

 

[nthach]

Japanese cars can use 3 types of pump to strainer attachment - one is a simple hose, another is a clip onto a pipe, and the 3rd is a weird coupling.

 

[mechtech2]

This sounds different than the normal whine associated with a pump going south.
A hard rattle? Broken baffling in the tank?

 

[gathermewool]

Originally Posted By: mechtech2
This sounds different than the normal whine associated with a pump going south.
A hard rattle? Broken baffling in the tank?


I thought it was originally an exhaust heat shielf, a loose baffle or possiby the fuel pump hanger rattling against the inside of the tank. The sound does not change, however, when I lift the pump/sending unit assembly up off its mount a couple of inches so that the pump is running with the only supporting structure for the assembly being my fingers. The car was running at the time.

Here's a clip of the sound. The amplitude of the noise with the camera right next to the cover is how it sound where I'm standing; the mic isn't very sensitive. Also, when I put my ear to the cover I hear the electical whir of the motor, but every few seconds it seems to skip a beat, like: weeeeeeeeeeeeeeeeeeeeeeyouweeeeeeeeeeeeeeeeyouweeeeeeeee, where the "you" part is where the electrial whir seems to skip a beat.

 

[Alan]

A clean and new fuel filter can quell noise in many cases.