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Loud Fuel pump!?!

jrowell

NAXJA Forum User
Location
Bakersfield
Little Back story first (soory this is long) ... 87 xj. My tank was dented in from wheeling (and would only hold about 10 gallons) so I got a new one from the salvage yard. Before I put it in I dod the tank mod where you raise the Air outlet thingy-ma-do so you can get more fuel in the tank. I then put the stock fuel pump in and everything was good. It fills a little slow, but I'm able to get over 20 gallons in.

On to my problem: on the first trail run, the pump started making a loud buzzing sound. Like it was vibrating against metal. I believed that the pump was damaged in the dented tank making it's foot not "seat" in the tank. I bought a new pump and installed it being careful to get it to seat properly. Just took it on it's first run today. Drove it about 20 miles to the trailhead no problem. After about 1/2 hour of wheeling it starts making the same buzzing sound. It's pretty loud and exactly like the stock one. The pitch does not change with throttle. Stopped for a break and turned it off. Turned the key back on... and no sound. After about 10 minutes started it back up and it sounds normal. After about an hour of wheeling it starts again. I drive it about 1/2 hour more till lunch and shut it off. After lunch start it up and all is good again. Doesn't make a sound for the rest of the day (about 2 hours of wheeling)

I tried removing the fuel cap while it was buzzing thinking maybe it was not venting or something. No "swoosh" when the cap came off and no change to the pump sound. I pulled the filter and blew through it and it seemed like it wasn't plugged. I'm kinda stumped on this. Is something with the fuel tank mod I did screwing up the pump?

Any theories would be greatly appreciated!
 
Let me guess... Airtex?

Mine does the same exact thing if I feed it ethanol blend. Pure gas and it doesn't scream as loud.
 
This is odd, but I got a very loud buzz from the FP area a while back when I was working on my battery (actually cleaning up and putting a homemade anti-skid mat under it) the heep wouldn't start, and when it wouldn't start the FP would make a very loud noise. Come to find out that the ground cable from the battery terminal to the engine block was loose at the block, tightened that up and everything was all better. Is that your problem? dunno...
 
Also might try a gas cap. Fuel tank not venting pressure properly can cause the fuel pump to work harder than it should. When you fuel up is there a lot of pressure released when you take off the cap?
 
"Let me guess... Airtex?"
Yes... couldn't find anything negative about them... until after I installed the dang thing!

" Fuel tank not venting pressure properly can cause the fuel pump to work harder than it should."
I thought that too... tried taking the cap off and letting it idle for awhile. Made no difference. The cap is only a couple months old (Damn smog guys!)

"Come to find out that the ground cable from the battery terminal to the engine block was loose at the block, tightened that up and everything was all better."
I like solutions that don't cost me anything... I give it a try!

"have you checked/changed your fuel pump ballast resistor on the inner fender? "
As far as I know, 87's do not have one of these...
 
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Maybe I'm getting too much gas in it and the fuel level is above both the gas inlet and the other port. That's creating a problem for the pump during that time until the gas gets 3/4 level or below? That's my theory right now... Only problem is that it has yet to have the problem on the street (although I have only done 3 fills, and never drive the heep more than 10 miles)
 
When you moved the pump over, did you reinstall the rubber "stopper" that goes on the bottom of the pump and fits into the bracket in the bottom of the tank?
 
When you moved the pump over, did you reinstall the rubber "stopper" that goes on the bottom of the pump and fits into the bracket in the bottom of the tank?

Yes... and the new pump assembly came with one also...
but that is what the sound is like. Like it operating directly on metal and vibrating against it.
 
Re: Loud Fuel pump!?! Low Fuel pump Voltage?

Still investigating this issue. Got the volt meter out today to find at the fuel pump harness i'm getting: Red wire- 9 volts. Orange/middle wire- 3 volts.

I'm guessing low voltage could be the cause of my loud fuel pump. Any ideas as to WHY it is so low at the harness?
 
I'm curious what you find. My FP makes the same noise...mostly when it's hot. One time, I loosened the cap to find a lot of pressure in the tank (whooshing sound from the cap). Maybe a replacement cap will fix the noise?
 
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