How should your fuel pump sound?

[JHZR2]

Hi,

the fuel pump in my 91 BMW 318i is in the tank itself. The pump is located just under the rear seat, through an access hole that has a bolted down cover.

Ive always heard it when running. Just a little buzz. This is similar to the (apparently oversized) fuel pump in my 98 chevy (which is loud because its right under the rear fender, so I can hear it when outside of the truck.

The pump has quieted down at idle since Ive used FP60. Its lubricity is definitely confirmed in my application.

The thing with the BMW is the following:

(a) my car nearly fails NOx emissions test. maybe this has to do with output

(b) most importantly, the pump makes more "dynamic" noise now. Maybe it always did, and I didnt notice it because my diff was noisier, but one way or another, I note it more now. Its a funny sound, a combination of a 'sshhhhhh' sound and an electric buzz. it does not sound bad, but its very noticable that depending on throttle, the pump makes a higher or lower pitch sound. Granted, this makes some sense - at low throttle, more fuel is returned, so there may be less (?) loading on the pump? owever, it seems to me that the flow should be constant, and there be more return at low fuel utilization, and less flow at high utilization, but the pump sound should be constant. If the pump is weak, maybe the engine is slightly leaner.

Do pumps always make different noises as throttle changes? Or is mine on the way out?

Thanks!

JMH

 

[Mike242GT]

Is that a Bosch LH-Jet system? I see listings for Bosch injectors and idle air control motor, but Hella fuel pressure regulator and throttle switch for your car. In any case, when fuel pumps start making noise, I always suspect the FPR.

If your FPR is like the ones on my Volvos, they have a vacuum hose going to a fitting on the intake manifold and regulate the fuel pressure based on manifold vacuum. If you pull the vacuum hose off and get a dribble of fuel out of the hose, you probably have a bad FPR (there's a diaphragm inside that cracks).

Another quickie test of the FPR is to (with the engine off) pull the return line to the fuel tank off the fuel rail, and attach several feet of extra fuel hose - enough to run from the return side of the fuel rail to a five gallon bucket on the ground. With the engine at idle, you should get a really strong stream of fuel from the hose, like between 1/2 and 1 gallon per minute, which will then decrese as the throttle opens. If you are getting nothing, or just a very weak stream of fuel from the return line at idle, this is also a sign of a bad FPR.

 

[chas3]

fuel pumps make strange noises. check your repair guide for the proper psi and measure at the test port on the fuel rail. its pretty easy.

 

[srivett]

The dead OEM pump in my '87 E150 didn't make a peep. The replacement sounds like a beehive. It makes a real racket but it works. I can't recall the manufacturers name but I'll never buy anything from them again. It'll come back to me when I'm looking for parts.

It came from Canadian Tire about 3 years ago.

Steve

 

[andyd]

how old is the fuel filter? If it is partially clogged . it may be straining the pump.

 

[brianl703]

The FPR for my car was $12 (the original was made by Bosch). At that price I didn't even care to test it, I replaced it since it's under the intake manifold and I had that off to replace all the fuel injectors anyway. (17 year old car).

If your car has a test port for fuel pressure and you can get a gauge, it should get higher as the intake manifold vacuum drops.

 

[Jim 5]

I'd do the simple things like andyd said and change the filter first.

Do a search on some of the bmw boards, I think the e30 bmw's are known for fuel pump/ fuel transfer pump failure.

Check out this article for the skinny:

http://www.unofficialbmw.com/repair_faqs/transfer_pump.html

- looks like some guys are using an ac delco pump as a replacement.

...or google "BMW e30 fuel pump"

Not to mention your '98 Chevy truck. They are unfortunately known for this as well. My '98 K1500 had its fuel pump die at around 120k miles. This was in the year 2000, and the pump was really expensive. There wasn't any aftermarket pumps available yet. I should have changed the fuel filter, but I didn't think of it when I bought the truck used. The repair shop said it was nearly clogged.

It was really noisy for about 3k miles before it cr*pped itself. I was able to limp it about 20 miles down the highway to the nearest chev dealer.

Anyhow..protect those pumps by making sure they're not trying to overcome a clogged or near-clogged fuel filter.

 

[JHZR2]

the truck made the loud buzz since new... no issues there.

Fortunately my bmw does not have the failure prone dual pump setup.

Filters are relatively new on both, once there arent thunderstorms every night, Ill be changing the fuel filter.

JMH

 

[T-Keith]

Some pumps are louder then others, in-tank pumps are quieter on a full tank for obvious reasons, out of tank pumps will be louder. I've noticed my pump on my 88 Lesabre gets loud when the tank is low and I hit the brakes, but FP helps.

 

[andyd]

my 528es have the 2 pump set up. All 3 run fine with dead in tank (transfer pumps) Only issues I have had are with 15yr old fuel filters. My 88 has over 300 k on its original main pump and the transfer has been dead for the last 9 yrs. Does the noise get worse when the tank is low?