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Possible Fuel System Issues (Weird Noises)

CaliMeatWagon

Cause of Head Scratching
Joined
Jun 29, 2011
Location
Stockton, California
1991 745T w/ LH 2.4

Yesterday I noticed this weird humming noise coming from the center of the car. I didn't pinpoint the sound, but when I put my hand on the inline fuel filter its vibrations matched with the sound. And when I filled up with gas, the sound went away.

So I'm guessing it was because I was low on fuel, but it only took 12.6 gallons to fill up and I know I have a 16 gallon tank. And my previous 91 740 never made those noises even when it was on E.

So what could be going on here?

For some extra info that may or may not be pertinent back in July I had to clean out the tank and replace the in tank fuel filter because it had been sitting for 7 years. And two weeks ago I replaced the inline fuel filter. Also, my gas gauge doesn't work (no signal at sensor wire) so I have no idea what it would have read when the noise was going on.
 
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My first thought was a full tank is easier for the pumps to pump, but a 4 gal decrease probably isn't much... personally I'd just make sure to have a pump on the shelf for if or when it does crap out.

Also, most of my bricks have had a bit of a hum from the pump, is it much louder than normal?
 
My first thought was a full tank is easier for the pumps to pump, but a 4 gal decrease probably isn't much... personally I'd just make sure to have a pump on the shelf for if or when it does crap out.

Also, most of my bricks have had a bit of a hum from the pump, is it much louder than normal?

Oh it was super loud. I could hear it from inside the car with the engine running and the windows rolled up. I honestly thought it was my transmission going out at first.
 
My first thought was a full tank is easier for the pumps to pump, but a 4 gal decrease probably isn't much... personally I'd just make sure to have a pump on the shelf for if or when it does crap out.

Also, most of my bricks have had a bit of a hum from the pump, is it much louder than normal?
Mine normally hums when I start getting in the red

I recorded this last night. It was dark and my phones a potato, but hopefully this helps (you may have to turn it up):

 
Same exact hum as mine

Any clue as to what causes it? I never heard it in my NA 740 and I used to run that one low all the time. This one I have no clue how much gas so I'm always topping it off and I think 13 gallons is the lowest I've gone. And this is the first time I've heard this noise.
 
I would definitely be looking at the in line pump. If the noise changes after a fill up, id be buying a pump. If it's running fine, then I'd just wait and see what happens. AAA is your friend. Get the thing back to you driveway or whatever parking situation and swap it out with a new unit if it dies. I definitely get a decent hum in my bricks, though the video you posted does sound a bit loud. Maybe just turn up the radio....idk. wasnt planning on the fellas coming over for a whiskey and beer night so im feeling all sorts of "fuck it, ride it it till it doesn't".
 
From experience, start spraying the fuel line connections down now with PB Blaster or similar, the banjo bolt on my fuel filter was really hard to get loose.
 
Any clue as to what causes it? I never heard it in my NA 740 and I used to run that one low all the time. This one I have no clue how much gas so I'm always topping it off and I think 13 gallons is the lowest I've gone. And this is the first time I've heard this noise.
Something fuel pressure, on mine I believe a weak in take pump makes my upgraded main pump work harder to supply the car. Likeyly weak from the previous owner wiring the in tank pump backwards, and the more powerful main was still able to suck through it and run the car
 
Something fuel pressure, on mine I believe a weak in take pump makes my upgraded main pump work harder to supply the car. Likeyly weak from the previous owner wiring the in tank pump backwards, and the more powerful main was still able to suck through it and run the car
If there's a clog or restriction on the intank pump you might get enough pressure drop in the line to get cavitation. But it seems kinda surprising considering the relatively low pressures involved. I suppose gasoline does vaporize more easily though...

 
I would definitely be looking at the in line pump. If the noise changes after a fill up, id be buying a pump. If it's running fine, then I'd just wait and see what happens. AAA is your friend. Get the thing back to you driveway or whatever parking situation and swap it out with a new unit if it dies. I definitely get a decent hum in my bricks, though the video you posted does sound a bit loud. Maybe just turn up the radio....idk. wasnt planning on the fellas coming over for a whiskey and beer night so im feeling all sorts of "fuck it, ride it it till it doesn't".

Yeah, that sounds like a solid plan. You have any experience with "Ultra-Power" or "Carter" parts?
 
The main pump is generally very quiet when being properly fed by the in tank pump. When they sound like yours does it is a warning sign. You may have a rotted off hose in between your in tank pump and the steel tube on the sending unit, or, a dead in tank pump. Remove your fuel line from the rail and put the end in a milk jug. Disconnect of of the two wires powering the main pump and cycle the key on and off several times to see of the in tank pump is actually pumping fuel. If not, replace it soon or you will be replacing both pumps before long.
 
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