Fuel Pump Question

[Bayarea Q]

I've read that the classic sign of a bad fuel pump is the loud humming from rear of car. My question is I can hear my pump humming sometimes when the tank is low.....around a 1/4 tank. But above 1/4 tank I don't ever hear it. Is this normal? Or do you guys think it's on it way out? 95Q 92K.

Q45 tech stated that his pump lasted to about 140K. So maybe it's normal for the pump to be louder when the tank is low? As I would assume the pump to hum all the time when bad, regardless of how much fuel is in the tank.

[natsoundup]

Some folks make sure their tanks never get below 1/2.... so they don't put extra strain on the pump...

I don't know if this is a myth or not...

my 90q has 151k.... I have only heard the hum once.... for a few seconds.... I will replace as soon as I hear it two days in a row....

[Bayarea Q]

Yep, Q45tech gave that advice....which I appreciate and follow. Not that I would ever doubt Dennis, but common sense would lead me to belive it's true.

It's the main reason why I don't know how the pump when low on gas, because I never let it get low. I just happened to be lazy the other day and didn't want to stop on my commute home. The next morning (1/4 tank) it seemed to be humming. Went away as soon as I filled the tank up. I also heard the pump once before after the car sat for 2 weeks. Went right away again, when I filled her up.

151K on the origional pump? Not bad......

[DAEDALUS]

It shouldn't make much of a difference. The pump can deliver over 50psi if I recall. The difference between a full tank and an empty tank is maybe 30" at most. Fuel weighs about .026lbs/in^3. The 30" head means the fuel pump is working against another .8 psi on an empty tank, less than 2% difference.

[Bayarea Q]

In that case it seems like if the pump is humming when low on gas that it's on it's way out.......Guess it's time to swap out the pump. Is this a DIY? Or am I better of letting the pros do it?

[DAEDALUS]

It is DIY with about 4 hours needed. There's a lot of good info already posted. Do a search, if you can't find them let me know.

[Bayarea Q]

Is it possible that the fuel modulator or fuel contoller unit is causing my pump to hum? I just want to ask before replacing my pump.

[DAEDALUS]

I don't think it will cause it to hum...but the humming doesn't tell you if the controller is good or bad.

[landtodd]

Okay, I don't think anyone stated the obvious . . . the pump is submerged in a half-full tank, completely exposed in a quarter-tank. Sure, you'll hear it better near E.

There has also been some informed speculation (thanks, Dennis) about the value of keeping a fuller tank to keep the pump submerged and better cooled.

This is a good preventive maintenance repair. Replace the pump before it takes the $450 controller with it!

[Q45tech]

Or ignore the pump and keep a spare pump and controller and tools in the trunk, so you can change everything by the side of the road in a rain storm while being 5 hours late to a very important appointment............I can just see the leather rear seats lying out on the grass with the owners head stuck in the rear window with kids and wife screaming because they are all jammed in front seat.

Preventative maintenance and repairs are just that to PREVENT this.

[911/Q45]

How about ignoring the pump and not carrying tools and spares so you can reenact that part of the movie "Vacation" in Elko, NV!

[Bayarea Q]

What I was trying to figure out is......if I had a bad pump or not, becuase I heard a low humming when the tank got low. I hear no humming when above 1/2 tank. The only reason I know of the whole humming thing anyway is because of this board, and I asked the qustion to determine if my pump is bad.....so I don't take out the expensive controller.

Thanks to those of you who offered your opinion.

Robert

[Q45tech]

Brand new pump with little gasoline in the tank, a middle aged human with Normal Hearing might hears a slight hum for 10 seconds just after cranking if all HVAC and radio were turned off.

Every hour of operation it just gets noiser and noiser;after 2500 hours [50-80,000 miles 5-7 years] it gets really noisey but everyone hearing response and amplitude curves are different..........heck many drivers/owners are deaf!

http://cartalk.cars.com/Column....htmlh ... nd...2.pdf

note from page 2 graph in above: how the pump current increases as the pressure increases [from 5amps>10 amps] and how the flow rate drops from 110L/hr to 60 liters per hour for a brand new pump.

"At one time the specifications for filtration was 70 micron (the strainer sock), 20-30 micron (the fuel filter) and 10 micron (the fuel injector upper screen). The utilization of gerotor high pressure pumps, new deposit resistant disc spray tip injectors and returnless (demand) fuel systems have required a tighter spec for the new models to be 33 micron (the tank strainer sock), 15-20 micron (the fuel filter) and 10 micron (the fuel injector upper screen). Special care must be taken with these new systems and pump replacement requires a tank flush to prevent a repeat failure.

http://www.asashop.org/autoinc...h.htm

[Q45tech]

As noted by the last link in above: the failure to clean [flush the fuel tank] accelerates the failure process in the replacement pumps...........why an oem pump may first fail at 120-140k and then the second pump 60k later and the third 40k later.......progressively getting worse as the concentration of trash build up.

Replacement pumps are only warranteed for 12,000 miles.