Wk 4.7 fuel pump issue

[Black Betty]

Im ripping my hair out here.  I had my 2006 jeep grand cherokee 4.7 fail on me last Saturday.  I brought back to my buddies toasty warm garage and started troubleshooting.  Pulling the connector at the pigtail from the tank, checking the frame side i had 12volts power with the key on, but no fuel pressure at the rail.

I dropped the tank, bench tested the pump, it would run intermittently.  So i replaced the pump and the filter sock, hooked everything back up started the jeep, and again, nothing.  No pressure in the rail.  I ran temp wires to the pump, started the jeep and it runs fine.  Checking the connector again, i found no voltage.  I cut the 12vdc positive wire out, measured 12vdc, so figured it was a bad connector.  I stripped back some wire on either side of the connector, and twisted the wires together, started the jeep and again nothing.

If i disconnect the pump, i have 12 volts across my red and black, if i connect the pump and measure i get zero.  If i jumper the pump to the battery, the jeep runs great.

Relay is fine, fuse is fine.

Any suggestions?

Next i will try a new ground from the pump and see if that works

[Immortal]

Next i will try a new Grand and see if that works

Fixed it for you.

I feel your pain buddy.

[cLAY]

Some thoughts:


You can have a bad line that will carry volts but not amps. It will show 12v on a meter but drop to zero when a load is applied. Try checking it with a test light. Also measure the resistance between the plug and ground and the plug the output pin on the fuel pump relay. Also try jumping the relay to rule it out. The same thing can happen in a relay.

Roll over switch/inertia switch kills power to pump in the event of an accident.  Seen a few Ford fuel pumps get incorrectly replaced due to these.

[Black Betty]

cLAY you are awesome.

Its not up and running yet, but it did find the problem.



Here is the wiring diagram for the fuel pump, Big 4 motors sent it to me today.

I disconnected the 12v positive at the pump, left the negative connected.  I took 8-10' of 12g stranded wire, and plugged it in to the hot side of the relay.  The jeep started.

Now i know this doesnt rule out the relay, but i do get 12v down at the pump with the ignition on, its only with the load of the pump the voltage drops out.  I will run a new 12g wire from the relay all the way back to the pump harness.  Then i can cap the old wire with a stakon cap and heat shrink, and the diode in the fuel pump circuit still protects the system.

Now i am out <$300, but it sure beats the $1800usd a guy from jeep forum paid for the same problem.

Thanks for your help, even you immortal with your smart arse comment.  Guess ill have to add your name to the on call schedule a little more frequently eh?

[pooljunky]

had same issue with my 01 tj.. i just rewired from computer

[cLAY]

Glad you were able to figure it out. I've been caught with the same issue before troubleshooting trailer wiring. Shows 12v on a meter but drops to nothing when a load is applied. Be aware that the wires usually run together in a harness. If the harness integrity is compromised then more than one wire may be affected. If you rewire around it you could have other electrical issues show up down the road.

[w squared]

Thanks for your help, even you immortal with your smart arse comment.  Guess ill have to add your name to the on call schedule a little more frequently eh?

Might as well do that. It's not like he has a Jeep to go wheeling in.

[Black Betty]

Its alive!

It was the wire after all this time.  Jeep starts great, next battle will be the drivers side exhaust manifold, and the sweating transmission flex lines.

Thanks again for the help, now its time to put everything back and clean up.  Thats after the victory beer lol.