Fuel pump humming

[KeithXJ]

I have a 93 XJ that I just bought. The fuel pump was humming when I got it. The jeep runs good but I noticed today that when I turn anything else on the humming gets worce and it also affects the volts gauge. Can somebody please help.

[souske]

Teach it the words?

Have you checked the voltage to the fuel pump?

[Reclipse]

Has the fuel pump been replaced? Is it an Airtex unit? If it is, these are normal to hum, gets louder the warmer it gets. Bosch or OEM seems to be the only way to go.

If it affects the voltage, it's very possible its on its way out. If you take it out to diagnose, be prepared to replace. Let us know what you find.

[Ecomike]

Output fuel line on the fuel pump, inside the gas tank may be going bad, leaking. My 89 Renix is noisy when it gets down to 1/3 of a tank of fuel. Quite as a church mouse with a full tank.

Is it a lifted jeep or stock?

[Jays siik xj]

Originally Posted by Reclipse

Has the fuel pump been replaced? Is it an Airtex unit? If it is, these are normal to hum, gets louder the warmer it gets. Bosch or OEM seems to be the only way to go.

If it affects the voltage, it's very possible its on its way out. If you take it out to diagnose, be prepared to replace. Let us know what you find.

My bosch pump is loud as hell!!! Especially when im running less that 1/2 tank.

[Ecomike]

I think they get hot and confused, start thinking they are Hummers, instead of Jeeps?

[kayle666]

mine goes from quiet to loud often i get worried when i cant hear it.

[cruiser54]

They will be loud if the rubber bumper falls off the bottom of the unit upon installation.

[Dragonslayer]

Check to see if the fuel pump resistor has been removed (or by-passed) by the previous owner. It's a white ceramic oblong-looking thing with 2 wires connected to it, and it's
mounted on the inner fender, driver's side, in the engine compartment.

Ordinarily when you first turn the ignition ON, the fuel pump is given 12V DC for (only)
a second or two in order to build up fuel pressure. After the engine is started and running, the fuel pump is given about 6V DC that comes through the fuel pump resistor.

Some owners will sometimes by-pass or eliminate that resistor as a "shade-tree fix"
for a fuel pressure problem.

The downside of that "fix" is that the fuel pump is then running at 12V DC at 100% of
the time (= spinning faster; is more noisy; wears-out faster).

[Ecomike]

I should add that while mine is only noisy when the gas level is below 1/3 tank, it is also only noisy enough to hear at about 40-60 mph on the 89 Renix. I thought it was bearing noise at first. And it is as quiet as a church mouse while priming before I crank it.

[cruiser54]

Originally Posted by Dragonslayer

Check to see if the fuel pump resistor has been removed (or by-passed) by the previous owner. It's a white ceramic oblong-looking thing with 2 wires connected to it, and it's
mounted on the inner fender, driver's side, in the engine compartment.

Ordinarily when you first turn the ignition ON, the fuel pump is given 12V DC for (only)
a second or two in order to build up fuel pressure. After the engine is started and running, the fuel pump is given about 6V DC that comes through the fuel pump resistor.

Some owners will sometimes by-pass or eliminate that resistor as a "shade-tree fix"
for a fuel pressure problem.

The downside of that "fix" is that the fuel pump is then running at 12V DC at 100% of
the time (= spinning faster; is more noisy; wears-out faster).

I agree with everything here except 2 things. Voltage is reduced to 8 volts, not 6. And, the reduction in voltage was not and is not to prolong pump life but to address the noise issue per a TSB in 1987.

[Ecomike]

And it is probably closer to 10-12 volts with the alternator running at 14.6 V?

[cruiser54]

Originally Posted by Ecomike

And it is probably closer to 10-12 volts with the alternator running at 14.6 V?

More than likely. The resistor just "takes the edge off" the pump RPM.

[riverside]

Is it necessary to drop the tank when installing the fuel pump? 92 XJ 4.0 thanks

[cruiser54]

Nope