Fuel Pump Dead? - JeepForum.com

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post #1 of 17 Old 07-30-2012, 06:15 PM Thread Starter
DeejayZeejay
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Fuel Pump Dead?

Well I picked up this 88 Jeep MJ with a 4.0 5 speed a couple weeks ago. Ran pretty good, horrible tires causing death wobble(right front tire was seperated). 123k miles. $1275 and it was mine. Changed most the fluids(eng oil, gear box and diff). Tune up and new tires. Seemed to crank a little longer than usual but always fired up.... Last week it wouldnt start. Had to use ether and mess with it to get it going. Always had a loud humming from the fuel pump. Now at work, went to go on a run and wont start up. Primed it, gave it ether and nothing. Hit the fuel rail valve and no gas came out. And I hear no humming from the pump. Fuel pump died? Probably original to.


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post #2 of 17 Old 07-31-2012, 07:02 AM
Pete M
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clean the ground located behind the drivers side taillight. worth a shot at least.

-88 MJ; 4.0L, ex-2wd, TJ ax15/231, 78 Ford D44 w/spool, 9" w/posi, 33" trXus MTs, custom roll-bar/bumpers/etc.
Also an 86 MJ Metric ton and 2 '90 MJs
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post #3 of 17 Old 08-02-2012, 05:55 AM
cruiser54
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There's a rubber hose in the tank between the fuel pump and the external flange. They get pretty crapped out. Change fuel filter?
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post #4 of 17 Old 08-02-2012, 07:59 AM
97_4popper
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Check that ground as Pete said.
If you're not hearing the pump when you turn on the key, it's probably either the ground or the pump has given up the ghost.

90 MJ 4.0 4X4 5sp LB Pioneer Big Ton.
Truck contains parts from 3 MJs, 2 XJs, 1 TJ and a dishwasher.
http://img.photobucket.com/albums/v1...IMG_0101-2.jpg
Check out comancheclub.com...
My build thread: http://comancheclub.com/forums/viewt...hp?f=7&t=27756
Wifes: 97 TJ 2.5 4X4 5sp 31's stock. . . Slow but; reliable.
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post #5 of 17 Old 08-02-2012, 06:36 PM Thread Starter
DeejayZeejay
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Couple questions. The ballast resistor, does that control the fuel pump? Also im not familiar with this starter solenoid by the battery... Would either of those kill power to the pump?

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post #6 of 17 Old 08-02-2012, 07:05 PM
cruiser54
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The fuel pump gets a full 12 volts on cranking and then switches power to one side of the ballast resistor so it can reduce the voltage coming out to about 10 volts so the pump is quieter.
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post #7 of 17 Old 08-02-2012, 07:23 PM
Pete M
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Yup, power gets diverted to run through the resistor after the truck is running.

Have you checked for power at the pump? There are 3 wires at that connector: ground, power, and signal from the level sensor.

-88 MJ; 4.0L, ex-2wd, TJ ax15/231, 78 Ford D44 w/spool, 9" w/posi, 33" trXus MTs, custom roll-bar/bumpers/etc.
Also an 86 MJ Metric ton and 2 '90 MJs
Projects/wheelin' pics: picturetrail.com/petermontie
My email: petermontie@hotmail.com
ComancheClub.com/forums
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post #8 of 17 Old 08-03-2012, 09:05 AM Thread Starter
DeejayZeejay
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Im not getting power to the pump.... Which is brand new. My old pump was real loud when it did work.

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post #9 of 17 Old 08-03-2012, 01:08 PM
97_4popper
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You've checked it with a meter?

If you're not getting power to the pump, then check your wiring.

90 MJ 4.0 4X4 5sp LB Pioneer Big Ton.
Truck contains parts from 3 MJs, 2 XJs, 1 TJ and a dishwasher.
http://img.photobucket.com/albums/v1...IMG_0101-2.jpg
Check out comancheclub.com...
My build thread: http://comancheclub.com/forums/viewt...hp?f=7&t=27756
Wifes: 97 TJ 2.5 4X4 5sp 31's stock. . . Slow but; reliable.
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post #10 of 17 Old 08-03-2012, 04:45 PM
cruiser54
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Fuel pump relay may be bad:
Attached Thumbnails
renix relay center.jpg  
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post #11 of 17 Old 08-06-2012, 10:50 AM Thread Starter
DeejayZeejay
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So I checked the wires and all is good. Put a new ground connector at the pump. I left the pump out just to make sure it was good before going in. Nothing. Does the pump need to be installed in the tank to complete the ground? New relay, ballast resistor and the solenoid by the battery. Little stumped here now...

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post #12 of 17 Old 08-06-2012, 12:49 PM Thread Starter
DeejayZeejay
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Also tried to jump the pump from the relay and it sparked....

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post #13 of 17 Old 08-06-2012, 02:29 PM Thread Starter
DeejayZeejay
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After messing with it all day today, I have come to realize its the power wire from the pump to the cab.... Now I just need to replace that wire....hopefully.

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post #14 of 17 Old 08-06-2012, 03:39 PM Thread Starter
DeejayZeejay
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Problem solved! It was the 2 wire connector that goes through the top of the pump bracket. So I straight wired it through the hole with a grommet and some gas resistant sealant. What a pita....

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post #15 of 17 Old 08-06-2012, 03:51 PM
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Good job.
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