No power to auxiliary fuel pump

irunmiles · **Posted:** Fri Jun 08, 2018 5:07 pm

I've used a small, low pressure in-line fuel pump successfully for over 225,000 miles. It's a Mr. Gasket 12V pump, and I've powered it with the factory-installed wiring provided for the non-existant in-tank pump. The wiring harness is located under the rear seat. I recently had my transmission replaced and since I was focused on that, I did not notice that the in-line pump was not working until the day after picking up the Jeep from the tranny replacement job. I typically listen for the pump buzz when I click the key to auxiliary.

I checked the wiring at the pump and discovered no power. I checked under the rear seat at the harness, and no power there. I checked all fuses in both boxes and all are good. I checked the relay in slot 29 and its good. I'm wondering what to check next.

papaindigo · **Posted:** Fri Jun 08, 2018 7:41 pm

Check the FSMs at http://colorado4wheel.com/manuals/Jeep/KJ/ if you can read the wiring diagrams they might help. NOTE 06 manual is 1 document but 05 is in several sections to get all CRD stuff. For you purpose 06 will probably do.

Perhaps stupid question but IIRC that pump only runs if power is supplied AND the circuit is completed with a good ground back near the pump. No ground no circuit hence no power. Is the ground good?

rancherman · **Posted:** Fri Jun 08, 2018 8:14 pm

papaindigo wrote:

Check the FSMs at http://colorado4wheel.com/manuals/Jeep/KJ/ if you can read the wiring diagrams they might help. NOTE 06 manual is 1 document but 05 is in several sections to get all CRD stuff. For you purpose 06 will probably do.

Perhaps stupid question but IIRC that pump only runs if power is supplied AND the circuit is completed with a good ground back near the pump. No ground no circuit hence no power. Is the ground good?

I think you are correct.
Those pumps, if it's this type;

when they fail, are usually totally 'open' too.

Good idea on the checking the ground.

irunmiles · **Posted:** Fri Jun 08, 2018 9:48 pm

The ground is good and the pump did not fail. I removed and tested the pump and it transfers diesel fine. My problem is power to the pump. I actually installed a new pump since the old one has 225k miles on it. Pretty good service for a $30 pump. Any insight in solving the power supply problem will be appreciated.

Billybob · **Posted:** Sat Jun 09, 2018 3:29 am

As papindigo stated download the relevant Service Manual from the link supplied.

I personally hate the 2006 Wiring Diagram section 8W and prefer the 2005 documentation when trying to help out KJ owners here....use 2006 documents if really needed!

So I advise that you download the 2005 KJ Service Manual and climb into the wiring section 8W and trace back from the pump to see where the voltage has gone missing.....something may have been bumped when the transmission was worked on!

I will have a look at the diagrams and see if there is any useful information that I can provide. :wink:

Sergio del Castillo · **Posted:** Sun Jun 10, 2018 1:27 pm

I am planning to install an in-tank pump ( a recent misfortune event of my fault convinced me to do it) and I have been studying carefully the diagrams in the service manual and also in the globe box manual in addition to reading other forum members advises and past experiences.

I own a 2005 CRD Sports, built in Feb. 2005. The information contained in the inside of the cover for the Power Distribution Center do not agree in full with the information from the service manual pages 8W-10-3 and 8W-10-5.
1) There is no fuse in cavity F24
2) There is a 10A fuse in cavity F17 labeled "FUEL PRIMING"
3) Relay cavity R34 is labeled "RAD FAN HI"
4) Relay cavity R40 is labeled "RAD FAN LOW"
5) Relay cavity R38 is labeled "FUEL PRIMING PUMP"

I have not completed my research in the Jeep as yet, but I would say that, at least in my model, fuse F17 and Relay R38 are the ones providing power to the wiring for the in-tank fuel pump, so called "priming pump" by the factory, but not installed.

I have in hand already a 15PSI in-tank pump, listed for the 2005 Dodge 3500 diesel so modifications to the positioning tab will be required, and the correct wiring terminal for the modifications to the wiring harness as well as the proper gauge wiring and splice kits and not forget the grounding bolt.

Please keep us to date of your findings. They will help me a lot.

WWDiesel · **Posted:** Sun Jun 10, 2018 2:43 pm

Keep in mind, the CRD did not come from the factory with a fuel pump in the tank. So you will not find it shown in the wiring diagrams in the FSM for the diesel.
I normally just look at the gasser wiring diagrams since it does have a pump in the tank from the factory.
I think most have agreed that the wiring and relay is the same.

As to your problem, a simple test
using a 12v test light or volt meter, remove the relay and check to see if you have 12v at terminal 30. See FSM for diagram of relay connections.
if you do, jumper the relay socket from the 12v terminal 30 to terminal 87 going to the connector under the rear seat.
if you do this, your pump should run, if it does not, then you know your have a break or fault between the relay socket and the connector under the rear seat.
if all of this tests good, then the problem is in the control circuit for the fuel pump relay and is controlled by the ECM. I would be checking fuses very carefully with a test light or meter....

good luck and keep us posted as to what you find.

irunmiles · **Posted:** Mon Jun 11, 2018 8:48 pm

Can I just find an alternative power source for my little pump? I noticed that the throttle body runs as soon as I turn the key and stops about 5 seconds after turning it off. I unplugged the throttle body and jumpered the power to my little pump and it worked. Would it be an option to tap into the power supply for the throttle body? If not there, where else might I tap into?

joe_ · **Posted:** Thu Jun 14, 2018 10:35 am

There's already a power source intended for a fuel pump. Why would you want to connect it somewhere else?

No power to auxiliary fuel pump

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