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Fuel Pump Noise

xjerod

NAXJA Forum User
Location
maryland
I have a 91 XJ and i just installed a new Delphi fuel pump, now I am getting a humming/vibration noise from the pump. The odd thing is that if I disconnect the vacuum line to the Fuel Pressure Regulator (FPR) the noise stops. I am not sure if the issue is the fuel pump or the possibly the fuel filter. I also recently replaced the FPR but I put the old one back on and the fuel pump makes the same noise when the vacuum line is connected to either pump. The noise is constant while the Jeep is on. I am getting about 35PSI with the vacuum line connected and about 42 with it disconnected.

I have seen many people with similar issues but I do not want to buy another fuel pump and instal if it is going to do the same thing.

91 XJ
4.0
Automatic
 
I did and I made sure it was seated properly, I dropped the fuel tank to ensure it was put back together solid. I bought a new fuel filter today and I will see if that has anything to do with it.
 
I imagine the all hum to an extent but my old one did not and this new one is loud enough that I can hear it in the cab and even more so if I am behind the Jeep. I replaced the fuel filter and that is not it either...

Just weird that the vacuum line is effecting it because when I disconnect the vacuum line from the FPR the noise almost goes away. its like the pump is getting to much resistance and its causing it to make a noise.
 
Make sure you have more than a gallon or two in the tank and then see if it changes.
 
Pulling the line to the FPR changes the pressure at the rail, which changes the load on the pump to develop that pressure. They say that when a pump starts getting louder it's an indication that it will fail soon. 'They say' is to indicate hearsay/rumor/urban myth possible...
 
At this point I hope it is that I got a bad fuel pump even though its brand new... these things happen but my luck it is another XJ mystery issue.. why do I have to love my XJ so much? if it were a grand cherokee I would of gotten rid of it.
 
I would get an original Bosch from the junk yard and try it. Those aftermarket are junk. I still have the OEM pump in my 89 with 576,000 miles on it, but I do carry a Bosch spare under the seat.
 
I would get an original Bosch from the junk yard and try it. Those aftermarket are junk. I still have the OEM pump in my 89 with 576,000 miles on it, but I do carry a Bosch spare under the seat.


If you read what people write in these forums long enough, every aftermarket fuel pump made is a pos. Trying to sort though it all can be daunting. The consensus I get is that Bosch and Delphi are pretty good, but everything else is junk. Airtex seems to have the worst reputation of any name brand available.
 
Many, many years ago my 88XJ was "rear-ended" and the insurance company replace my fuel tank and fuel pump. That pump developed a "hum". I did a search for a "fix" and found one that required removing the fuel pump and trimming a metal bracket/plate to eliminate the hum. I decided to replace the fuel pump when it failed and not before. That was about 400,000 miles ago. That fuel pump still works just fine and the hum appears to have disappeared. The check valve, in the fuel pump, then failed and I corrected that by adding an inexpensive external check valve.

Best regards,

CJR
 
Did you trim the metal bracket that holds it to the gas tank? I guess that could be a vibration spot, I have a new fuel pump I was going to instal today but I will give that a try to see what happens. I also noticed that I am not hold fuel pressure at the rail so it could be that there is an issue with the valve on the pump and I was already considering the check valve.

Thanks
 
To clarify. I never pulled the fuel pump. If you're considering an external check valve, get the all aluminium ones that are sold.

Best regards,

CJR
 
Soooo.
I'm somewhat of an expert on this topic.

here's my 2cents.... (7 fuel pumps in the last 15 years on my XJ)

Before I remove the fuel pump ballast. I never heard the pump.

After I removed it I can hear the high pitched whine.

Install a ballast if it really bothers you.
 
Blue3fan,
I just ordered a ballast to replace the one I have.. and man that would be great if it corrects the issue. I have another new fuel pump just in case but I will try the ballast first since its a quick install.

Thanks
 
sooo....

What that ballast does.

The fuel pump gets 12volts through that plug.
A jeep factory engineer decided the fuel pump was too loud.
That ballast lowers the voltage. (I don't know the exact amount. you could voltmeter on it to check)
I smashed my ballast with a hammer once I figured out it was my issue and connected the wires. I perfer the noisy pump. and that pump is designed to work at 12v. not 9v or whatever jeep set it to...

But back to my point... if you already had a ballast and the jeep ran. replacing it probly not gonna fix this issue.

If yours is noisy it could indicate blockage in the lines. or like a really crap pump?
Bosch or nothing. those other pumps are 100% junk.
Last idea?? maybe double check diagrams of how its supposed to be assembled? maybe you have something loose?

When I was troubleshooting my issue I blew air through my lines and TONS of crap came out. so maybe u wanna clean ur lines too?

my intermittent dying issue was the ballast failing and corrosion on wires inside the fuel tank or bad grounds.... I fixed them all so cant say which...
 
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