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Odd Noise after fuel pump swap

M

MissouriXJ

NAXJA Forum User
Location
Mid Missouri
Ok, I picked up a 94 Cherokee the other day for cheap was pretty sure the fuel pump was out of it. So I pulled the pump out of my parts 93 Cherokee just to see and sure enough it fired up sputtered a bit but plenty of power.

Run great for the first day, now today it is taking longer to start not much but a few seconds. And I also noticed a extra loud humming from the pump on my way home today, like the sound you hear when you first turn the key on, but now its constant while your driving.

Here's my question, is the pump different from a 93 to a 94? Would something else cause this extra noisy pump now, was quiet in the 93 Jeep? I read one of the stickys about a noisy pump, but all pertained to a 93 so I wasn't sure if it was the same for a 94. Any help would be great, this Jeep set for a few months I think before I picked it up.
 
Ok, after doing some checking seems 93 Cherokee and 94 Cherokee have different pump numbers, so am I to assume they will not interchange and could that be my problem? Like I said it starts and runs, but makes noise now. Please someone give me some idea's before I drive this to much more. Thanks
 
Yeah mine is really loud, you can hear it inside the cab, and really bad when your behind it. With it running you can crawl under it and feel it buzzing all the way to the fuel filter.

Whats funny, is it is quiet when you start it cold of a morning or evening, but by the time I make the 15 mile drive home it has gotten really loud. So far hasnt effected performance so i am lost. Can anyone help on this or am I beating a dead horse herehasta
 
Two fuel pump "quieters":

The ballast resistor on the firewall.

The rubber "foot" on the bottom of the pump assembly fitting correctly into the lip in the tank.

Other factor: quality of the pump--I use Bosch.

And yes, there is a change in the 93/94 fuel pump. I didn't know that either.

PS--what was the condition of the pump-to-flange rubber fuel line? If it is deteriorated and leaking the pump will have to work harder.
 
I cant find the resistor on the 94, on the 93 it has one. Not sure what you mean by the pump-to-flange rubber fuel line? If it is deteriorated and leaking the pump will have to work harder?
 
The pump assembly to tank flange. From the flange to the pump assembly is a rubber fuel line.

Grab the 93 resistor and add it to the positive feed to see if that makes a difference.
 
joe_peters said:
The pump assembly to tank flange. From the flange to the pump assembly is a rubber fuel line.

Grab the 93 resistor and add it to the positive feed to see if that makes a difference.
Click to expand...

Ok, let me ask a stupid question, does it matter where I add it? On the 93 it is mounted to the inside of the drivers fender. There isnt even a place on the 94 for it. Think I might be better just grabbing the right year pump for this? I just assumed beings they were only a year apart they were the same pump.
 
I wonder if they "de-powered" the fuel pumps at the same time they eliminated the resistor. The resistor decreases the voltage to the pump except during cranking. To add a resistor, you would want to put it inline to the pump, but to replicate use during the earlier years, it would need to be fed differently while cranking and while running.
 
Probably just buy the right pump.

On the Renix era the ballast resistor is bypassed during cranking and at WOT.
 
joe_peters said:
Probably just buy the right pump.

On the Renix era the ballast resistor is bypassed during cranking and at WOT.
Click to expand...

Mine started making the noise last month.
I do NOT think it is a pump problem, rather a fuel line resonance problem.
Mine is a 1991 and may be an original for all I know (bought used 2 years ago).

Same syptoms, I can see the rubber portion of the fuel line vibrating when this happens after maybe 1-hour driving.

I've seen other posts where replacing a fuel pump alone does not stop the noise.
 
dennis461 said:
Mine started making the noise last month.
I do NOT think it is a pump problem, rather a fuel line resonance problem.
Mine is a 1991 and may be an original for all I know (bought used 2 years ago).

Same syptoms, I can see the rubber portion of the fuel line vibrating when this happens after maybe 1-hour driving.

I've seen other posts where replacing a fuel pump alone does not stop the noise.
Click to expand...

Get a pressure gauge and post up the readings, should be 30-31 w/vacuum applied to the regulator and 39 psi w/o vacuum.
 
joe_peters said:
Get a pressure gauge and post up the readings, should be 30-31 w/vacuum applied to the regulator and 39 psi w/o vacuum.
Click to expand...

Yea, pressures fine, Jeep runs good, just makes this noise after a while.
I usually run with 1/2 tank: Next run I'll fill it up first.
It's a trail rig, so I can experiment and hopefully help others out.

My fuel flter only has about 100 miles on it.
I plan on also getting a spare pump, then open the tank slowly and look for any missing rubber bumpers, gaskets or clamps.

Heck, maybe there is a rag n the tank !!
 
dennis461 said:
Yea, pressures fine, Jeep runs good, just makes this noise after a while.
I usually run with 1/2 tank: Next run I'll fill it up first.
It's a trail rig, so I can experiment and hopefully help others out.

My fuel flter only has about 100 miles on it.
I plan on also getting a spare pump, then open the tank slowly and look for any missing rubber bumpers, gaskets or clamps.

Heck, maybe there is a rag n the tank !!
Click to expand...

One thing that is fairly common is deterioration of the fuel hose inside the tank from the top of the fuel pump to the tank flange, and some one even had their just come loose.
 
Update,
Got down to 1/4 tank a week ago after a long run in South Jersey.
When back on pavement, I could not get the engine above 2000 rpm, sputtering and backfire through air cleaner.
Checked fuel pressure and flow yesterday, got 12-14 ounces in 15 second which I believe is good. Pressure at 40 psi.

Today is decided to start real work.
Pulled the fuel filter and line from tank to filter back-flushed it and found this..
677bad_gas-med.jpg


Now, My XJ is lifted and it looks like I can pull the pump without lowering the tank.
Is that correct?
 
Pretty sure that through 96 you can pull the pump assembly without dropping the tank, and that the 97+ with the plastic tanks you have to drop them as the flange is on the top of the tank.
 
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