Very Loud Fuel Pump - Jeep Cherokee

Nick1994

$50 Site Donor
Messages
13,309
Location
Phoenix, AZ
This is for my brother's 91' Jeep Cherokee 4.0L. It's been sitting for a few years and he replaced the fuel pump as the old one didn't hold fuel pressure, took cranking to get started. That pump is long gone.

The fuel pump is EXTREMELY loud. He's tried 2 Spectra pumps and now a Delphi, and they all sound basically the same. The old fuel pump was quiet. I helped him put in the Delphi last night and we stuck my phone camera in the fuel tank opening and saw a round rubber thing, which was to the original pump and we plucked it out. Everything else inside looked fine. Fuel filter is new, it did this with the old one too. He also removed the fuel tank skid plate incase it was rattling or something.

Fuel pressure is at the proper 49 psi spec. The Jeep runs great, power is normal, just the insanely loud fuel pump. Fuel pressure regulator was replaced at one point too. Also has new 4 hole injectors.

My brother was wondering if it has something to do with the ballast resistor? He replaced it with a new one and no change, and from his research it shouldn't run with the ballast resistor disconnected under the hood, but it does, and the sound is also the same if you bypass it from under the hood too.

It is quiet when you first start it, after a couple minutes it gets really loud.

Below is 2 videos. The first is me walking around it. The exhaust is also a little loud, it has a hollowed out cat at the moment. The second video is priming it with the key twice.


 
Messages
15,879
Location
NE,Ohio
that is fairly bizarre. good luck.
is there any kind of mounting gasket on the fuel pump?
is it touching the tank or suspended into the tank?

not familiar with install on those.
 

Nick1994

$50 Site Donor
Thread starter
Messages
13,309
Location
Phoenix, AZ
that is fairly bizarre. good luck.
is there any kind of mounting gasket on the fuel pump?
is it touching the tank or suspended into the tank?

not familiar with install on those.
It goes in at somewhat of a 45* angle, maybe a 60* and has a rubber o-ring.
 
Messages
5,628
Location
Fort Worth, Texas
The Ballast Resistor is there to reduce voltage to the Fuel Pump thus reducing operating noise. Under WOT.....There is a Ballast Bypass Relay that is commanded on by the PCM to give full voltage to the fuel pump.

Maybe the ballast resistor has been bypassed? I would look for wiring modifications......

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Messages
5,628
Location
Fort Worth, Texas
After looking at the diagram closer.......The PCM actually de-energizes the By-Pass relay for full 12vdc to the fuel pump. A bad Ballast By-Pass relay would effectively By-Pass the Ballast Resistor!

As you can see in the diagram....The fuel pump power circuit is on 87A not 87.
 
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