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Unread 11-19-2012, 06:50 PM   #1
JeepComanche89
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No volts to the fuel pump

Well i went to try to start my comanche today after my engine swap (88 4.0 to 89 4.0). The engine will crank great, but no voltage is being sent from the fuel pump. Were thinking that it might be the fuel pump relay, but it looked fine. Any other ideas before i go replacing stuff. Thanks in advance.

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Unread 11-19-2012, 08:04 PM   #2
DeejayZeejay
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Check the wiring where it goes through the grommet to the inside of the tank. That was my problem. Pump was still good.
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Unread 11-19-2012, 08:18 PM   #3
cruiser54
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Do you for sure have spark?
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Unread 11-20-2012, 04:52 AM   #4
JeepComanche89
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Quote:
Originally Posted by DeejayZeejay
Check the wiring where it goes through the grommet to the inside of the tank. That was my problem. Pump was still good.
I have a brand new pump, so i know the pumps good. And I checked the plug that comes out of the cab with a meter and nothing was being sent.
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Unread 11-20-2012, 04:52 AM   #5
JeepComanche89
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Quote:
Originally Posted by cruiser54
Do you for sure have spark?
Starting is not the issue just yet because i know for sure the pump is not running.
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Unread 11-20-2012, 04:57 AM   #6
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Quote:
Originally Posted by JeepComanche89 View Post
Starting is not the issue just yet because i know for sure the pump is not running.
Do you have power at the ballast resistor on the driver's side inner fender?

How about to terminal #30 in the fuel pump relay receptacle?
Power to terminal #86 when key turned to Start?
ballast-resistor.jpg   renix-relay-center.jpg  
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If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

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My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 11-20-2012, 07:19 AM   #7
JeepComanche89
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Thanks, that helped alot. I will check today when i get home.
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Unread 11-20-2012, 07:35 AM   #8
97_4popper
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Ground for the whole back of the truck is a small wire behind one of the taillights. I just put a ground strap on mine from the cab to the bed and solved all of my problems.
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Unread 11-20-2012, 09:25 AM   #9
DeejayZeejay
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Just a strap by itself? Or did you connect anything with it?
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Unread 11-20-2012, 09:53 AM   #10
JeepComanche89
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Quote:
Originally Posted by 97_4popper
Ground for the whole back of the truck is a small wire behind one of the taillights. I just put a ground strap on mine from the cab to the bed and solved all of my problems.
Hmm, ill take a look because my bed is off right now and i just have the tank on the floor. But i dont think a ground could be the whole problem
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Unread 11-20-2012, 10:44 AM   #11
97_4popper
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Nothing else. Just a ground strap from the cab to the bed. The bed has a hard time with grounds sometimes so this is another place to be grounded from.
The cab has a good ground already so this just makes another connection.
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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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Unread 11-20-2012, 10:47 AM   #12
97_4popper
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Quote:
Originally Posted by JeepComanche89 View Post
Hmm, ill take a look because my bed is off right now and i just have the tank on the floor. But i dont think a ground could be the whole problem

It may not be the whole problem, but it is a known issue with these trucks. I found out about it when I replaced the bed when my son still owned the truck. He had an accident and we put a new bed on it. The fuel pump wouldn't fire. I found about the little wire behind the tail light. Then I added the ground strap.
I haven't had any electrical weirdness on the fuel pump or tail lights since I added this strap.
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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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Unread 11-20-2012, 10:48 AM   #13
97_4popper
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If your fuel pump is on the floor, then it could be your problem.
Run a ground wire from the tank to the chassis and see if the fuel pump fires.
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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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Unread 11-20-2012, 11:33 AM   #14
JeepComanche89
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I will definatly look into the ground. However im not getting any volts at the plug that comes from the grommet in the passengers floor pan. Im pretty sure its the resistor mentioned earlier is the problem. Im going to figure it out tonight
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Unread 11-20-2012, 02:08 PM   #15
JeepComanche89
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Is it possible that my comanche, 88 does not jave a ballast resistor tht was mentioned above? I cannot find any wires that would go to it.
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